Kepler’s Somnium: The Dream, or Posthumous Work on Lunar Astronomy

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KEPLER’S Somnium

He

fables, yet speaks truth. MATTHEW

ARNOLD

Empedocles on Etna

Johannes Kepler

KEPLER’S

Sommum THE

DREAM, ON

OR

POSTHUMOUS

LUNAR

WORK

ASTRONOMY

TRANSLATED WITH

A COMMENTARY

EDWARD

THE

UNIVERSITY MADISON,

OF

ROSEN

WISCONSIN

MILWAUKEE,

LONDON,

BY

1967

AND

PRESS

Published by The University of Wisconsin Press Madison, Milwaukee, and London U.S.A.: Box

1379, Madison,

Wisconsin

U.K.: 26-28 Hallam Street, London,

53701 W.1

Copyright © 1967 by the Regents of the University

of

Wisconsin

Printed in the United States of America by V ail-Ballou Press, Inc. Binghamton, New Library

York

of Congress Catalog Card Number

65-20639

To Sally DEARLY

BELOVED

HELPMATE

Preface

Since the first edition of Kepler's Sommnium, or Dream, in 1634, the Latin text has been reprinted but once: in Volume VIII of Christian Frisch’s edition of Kepler's works, 1858-71. A new edition of the Latin text is scheduled to be included in Volume XII of Kepler’s

Gesammelte

Werke,

Franz Hammer and Martha There were two partial in the nineteenth century: 4, and by Ludwig Günther

now

under

the supervision

of Dr.

List. translations of the Dream into German by Edmund Reitlinger in Sirius (1871), in his book, Keplers Traum vom Mond

(1898). Of the latter Günther says: “In order not to overload the book, I am including only those Notes which in my opinion are

necessary for a general understanding. I hope that I have right selection." ! A complete translation of the Dream into English was by Joseph Keith Lane as a candidate for a Master of Arts Columbia University in 1947, and has not been published. English version of the Dream,

made the prepared degree at A partial

by Everett F. Bleiler, appeared

in

the anthology Beyond Time and Space (New York: Pellegrini and Cudahy, 1950; selected and introduced by August Derleth). Kepler’s Dream (Berkeley and Los Angeles: University of California Press, 1965), contains a translation by Patricia Frueh Kirkwood,

and an interpretation by John Lear. My own translation was made from the copy of the 1634 Sommium at Columbia University, where I have been a member of the University Seminar on the Renaissance for many years. The Columbia University copy, which lacks the title page and dedication, is presumably one of those circulated after 1630 by Jacob Bartsch, Kepler's son-in-law, before the Dream

was completed in

1634 by Kepler's son, Ludwig. The missing title page was available in Max Caspar's Bibliographia Kepleriana, and the dedication in Frisch's edition. 1. Günther,

Traum,

p. xxi.

vil

vill

Preface

Kepler

was

aware

that the text of his Dream

required

tion. For this reason he added 223 Notes, explaining:

clarifica-

In my treatise there are as many problems as lines. Some of these problems have to be solved by astronomy, some by physics, and some

by history. But what would you do?

How

many

men

will think it

worth their while to solve these problems? People want pastimes of this kind presented to them superficially, and they are not inclined to wrinkle their foreheads over a puzzle. Therefore I have decided to

solve all the problems by means

numerical order.?

of Notes, which

follow the text in

But for the modern reader many of these Notes themselves require clarification. For this reason I have added my own comments on

Kepler's Notes. His Notes are marked in the text by numbers en-

closed in parentheses within the line, whereas my footnotes are indicated by superior figures. Unless otherwise stated, all translations throughout this book are my own. Editorial interpolations are always indicated by square brackets. Many private individuals have facilitated the preparation of this

book, notably Professor William H. Stahl of Brooklyn re Dr. Lucia Rossetti of Padua; Father Joseph T. Clark, S.J.,

Canisius College, Buffalo, New York, and his Roman agent, Eae

Mario Colpo, S.J.; and Mrs. Nancy Sabra of Alexandria, United

Arab Republic. I am indebted to Miss Martha List for numerous courtesies, including a microfilm of Diehl's reproduction of the engraving of Philip III, Landgrave of Hesse-Butzbach, and of the

portrait of Matthias Bernegger; to the Swiss Federal Astronomical Observatory in Zurich for a photocopy of Bartsch's 1627 broad-

side; to the American Numismatic Society for finding and measur-

ing a certain coin; to the Cleveland Public Library for lending its copy of Diehl on interlibrary loan; and to the State and University

Library of Hamburg for confirming the date of one of Bernegger's letters. For permission to reproduce illustrations, my grateful thanks are due to the C. H. Beck'sche Verlagsbuchhandlung of Munich for the

portrait of Kepler and the title page of the 1634 Somnium; to the Historischer Verein für Oberpfalz und Regensburg and the 2. Gresam.

Werke,

XVIII,

143:19-25.

Preface

1X

Naturwissenschaftlicher Verein zu Regensburg jointly for the portraits of Bartsch and Mastlin; to the Kepler Research Institute at

Weil der Stadt for the portrait of Bernegger; and to the Ober-

osterreichischer Landesverlag of Linz for the Landhaus. Part of the work on this book was done during my tenure of a National Science Foundation grant, which enabled me to visit the

Kepler

Research

Institute

at Weil

der Stadt,

West

Germany,

where I derived great pleasure and profit from conversations with the Director, Dr. Franz Hammer, and his collaborator, Miss Martha List. I was able to do research also at the Austrian National Li-

brary in Vienna, where I enjoyed Dr. Josef Mayerhófer's energetic and enthusiastic cooperation, which I acknowledge here with deep-

est gratitude.

Bloomington, Indiana 1963

E.R.

Abbreviations of Works Cited Frequently

Frisch Joannis Kepleri astronomi opera omnia, ed. Christian Frisch. Frankfurt/Main and Erlangen, 1858-71. Gesam. Werke Johannes Kepler. Gesammelte Werke, under the direction Walther von Dyck and Max Caspar. Munich, 1937——. Günther, Traum

Keplers Traum vom Mond, 1898.

tr. and ed. Ludwig

Günther.

Somnium Johannes Kepler. Somnium, seu Opus Postbumum Lunari. Zagan and Frankfurt/Main, 1634.

of

Leipzig,

de Astronomia

In addition, works mentioned in the footnotes are cited in shortened form if the titles are listed in the Bibliography. All other works are cited in full in the first reference to them.

Xl

Contents

Preface Abbreviations of Works

Cited F requently

List of Illustrations Introduction

The Dream Kepler’s Notes on the Dream Kepler’s

Geographical

Appendix

to the Dreaz

Kepler’s Notes on the Geographical Appendix Appendix A

Jacob

Appendix

B

Ludwig Kepler

Appendix

C

Bartsch

Kepler's Lunar Dissertation of 1593

Appendix D

Kepler's Translation

Appendix

E

Kepler and Donne

Appendix

F

Kepler's Legendary

of Plutarch's Moon Account

of Aristotle's

Appendix G

Death Oddur Einarsson, Bishop in Iceland

Appendix H

Kepler's

Concept

of Gravity

Concept

of Inertia

Appendix

1

Kepler's

Appendix

J

The

Cold

of Quivira

Appendix K

David

Appendix

Paul Guldin The People of Lucumoria

L

Appendix M

Fabricius

Bibliography

245

Index xii

List of Illustrations

frontispiece JOHANNES KEPLER From a reproduction in Gesammelte Werke, XVIII, of a portrait of himself which Kepler sent to Bernegger on September

25, 1620. This oil painting reached Strasbourg on September 28/Octo-

ber 8, and when Bernegger saw it, he decided to have an engraver, Jacob von Heyden, copy it. On February 23, 1627, Bernegger informed Kepler that the oil portrait had been installed in the public library of the University of Strasbourg, which still possesses it. According to the inscription on the portrait, the dedication ceremony took place on New Year’s Day, 1627 (Gesam. Werke, XVIII, frontis-

piece; No. 893:7-8; 46:41-44; 281:47-48).

page 2 TITLE PAGE OF THE 1634 Somnium From a reproduction of the 1634 title page in Caspar, Bibliographia Kepleriana, Facsimile No. 86.

following page 136 RUDOLPH

II, HOLY

ROMAN

EMPEROR

hüller, Conterfet Kupfferstich PHILIP

III, LANDGRAVE

OF

From

(Leipzig,

Franz

Christoph

Kheven-

1721-22), I, facing p. 29.

HESSE-BUTZBACH

This

engraving

was

orig-

inally published in a volume mourning Philip's death (Monumentum exequiale, Frankfurt/Main, 1647). The author had been Philip's court preacher, Martin Erythropilus (a grecized form of "Rothut" or Red Hat). From Erythropilus’ Monumentum, which is now extremely rare,

the

engraving

was

reproduced

as the

frontispiece

of

Wilhelm

Diehl's Philipp, Landgraf von Hessen-Butzbach, Hessische Volksbücher, No. 5 (Darmstadt, 1909). This illustration is taken from Diehl’s reproduction. XV

XVI

List of Illustrations

FREDERICK V OF BOHEMIA, THE “WINTER Khevenhüller, Conterfet Kupfferstich p.

KING" From Franz Christoph (Leipzig, 1721-22), I, facing

218.

WALLENSTEIN,

KEPLER'S

LAST PATRON

From

hüller, Conterfet Kupfferstich (Leipzig,

Franz Christoph Kheven-

1721-22), II, facing p. 424.

MICHAEL MASTLIN, KEPLER'S TEACHER From Stóckl (ed.), KeplerFestschrift, facing p. 337. The original painting, which is in the possession of Tübingen University, bears the following inscription: “This is a portrait, done in the year 1619, of Michael Mastlin, born at Góp-

pingen on September 5, 1550, since 1584 professor of mathematics at the famous university of Tübingen." MATTHIAS BERNEGGER, KEPLER'S FRIEND Reproduced from the original engraving in the possession of the Kepler Research Institute at Weil der Stadt, West Germany. This portrait was done by Melchior Haffner, who came from Ulm, but worked as a copper engraver in Augs-

burg, of which he executed a ground plan in 1629 after a design by

Johannes Umbach. This Melchior Haffner is to be distinguished from his better known son of like name. The foregoing statements, based on unpublished information, were first printed by Albrecht Weyer-

mann, Neue bistorischGelehrten und Künstlern

biograpbiscb- artistische Nachrichten von ... aus... Ulm (Ulm, 1829), pp. 152-53.

JACOB BARTSCH, KEPLER'S SON-IN-LAW From Stöckl (ed.), KeplerFestschrift, facing p. 200. The original painting is a miniature, about 3 A" x 4" in its largest dimensions. It was painted in oil on a copperplate and was handed down from generation to generation within the

family, until it was sold by direct descendants of Kepler's daughter, Susanna, to the Pulkovo Observatory, in Leningrad, in 1876 (ibid.,

Pp- 196-97). WILLEBRORD SNEL From Johannes van Meurs, Athenae batavae den, 1625), p. 296.

(Lei-

THE LANDHAUS IN LINZ, WHERE KEPLER WAS LIVING WHEN HIS LIBRARY WAS SEQUESTRATED From a drawing by Friedrich Bernhard Werner of

Silesia, a copper engraving was made by Martin Engelbrecht of Augsburg about 1750. This illustration is taken from the print of the Engelbrecht

engraving

in the municipal

graphically reproduced in Eduard (Linz, 1950), Plate 17.

collections of Linz, as photo-

Strassmayr, Das Landhaus in Linz

Introduction THE AND

COMPOSITION

PUBLICATION

OF

KEPLER’S

DREAM

When Kepler was enrolled at Tübingen University, the students there were required to compose a number of dissertations or dis-

putations. One such composition, written by Kepler in 1593, dealt

with the following question: How would the phenomena occurring in the heavens appear to an observer stationed on the moon? Kepler had hit upon this ingenious device in an effort to overcome the deep-rooted hostility to the Copernican astronomy. According to Copernicus, the earth moves very swiftly. But the people who live on the earth do not see or hear or feel this movement. Yet they can watch the moon perform various motions.

These lunar motions, however, would escape detection by an ob-

server located on the moon, for the simple reason that he would be participating in those motions. Since the lunar motions would not be apparent to an observer there, by the same token the terrestrial motions are not noticed by observers here. ‘This seems to have been

the basic theme of Kepler’s 1593 dissertation (see Appendix C).

It was never presented at a Tübingen disputation, however, because Veit Müller, the professor in charge of those academic exer-

cises, was so unalterably opposed to Copernicanism that he refused

to permit Kepler's theses to be heard.' This rebuff did not dishearten the young student to the point of tearing up his work in disgust and throwing it away. On the contrary, he kept it and

bided his time until he would no longer be under the control of a

reactionary

and

unsympathetic

professor.

This

earliest draft

1. See Kepler's Note 2 on the Dream; and Gesam. Werke, XIII, 39:242-44.

XVI

has

XVII

Introduction

not survived—it was not mentioned in the first catalogue of Kep-

ler's manuscripts.?

That earliest draft was apparently left undisturbed for sixteen

years, during which

all sorts of things happened

to Kepler, both

good and bad. Among the good things was his appointment as Imperial Mathematician. In this capacity he lived at Prague, which was then the capital of the Holy Roman Empire. There he became friendly with Wackher von Wackenfels, an official whose hobby was astronomy. The two friends frequently debated a variety of

scientific questions,

sharply

but amicably.?

As

a consequence

of

such a good-natured disagreement Kepler pulled his 1593 student

dissertation out of a drawer and resumed work on it after a lapse of sixteen years.

In a public letter he remarked:

“Last summer we engaged in

these discussions to such an extent . . . that... I even founded a new astronomy, as it were, for those who live on the moon and,

to put it plainly, a sort of lunar geography." * Kepler's “lunar geography," as he calls it here, was written in 1609, since the public letter containing the remark just quoted about “last summer”

bears the date April 19, 1610.5 This second stage of Kepler's work

has been misdated, presumably because the Dream, or Posthumous

Work on Lunar Astronomy, as it was finally entitled, opens with a reference to the year 1608. But that is the year in which Kepler

imagines an event to have taken place about which 1609.

he wrote

in

Ordinarily Kepler refers to our book in its final form as the Dream. But in his Note 134 on the Drea he says: “. . . when I wrote the Lunar Astronomy, the declination of the magnet from the meridian was in some repute as though it were suitable for de-

termining the longitudes

of places everywhere.”

However,

Wil-

liam Gilbert's Magnet, which was published in 1600 and which was read by Kepler a few years later, caused him to reject magnetic

declination as a reliable indicator of the longitude of a vessel in the open water.? Hence, so long as Kepler still believed in an infallible 2. Royal

Society of London,

Philosophical

Transactions

printed, New York: Johnson, 1963). 3. Rosen, Kepler’s Conversation, p. 10. 4. Ibid., pp. 25-56. 5. Ibid., p. 48. 6. See fn. 243 on Kepler's Notes on the Dream.

(1674), 9:29-31

(re-

Introduction

connection

between

magnetic

X1X

declination

and

geographic

longi-

tude, what existed was his original student dissertation of 1593 or Lunar Astronomy.

work of the Dreazziz.

Around it, in 1609, he constructed the frame-

He devised this Dream framework in order to introduce a supernatural agency for the purpose of transporting a professional astronomical observer to the moon. A manuscript copy of this second stage was taken from Prague in 1611 and involved Kepler in the serious trouble which he recalls in his Note 8 on the Dreaz:. When that trouble finally came to an end, Kepler decided to have the Work printed so that everybody could see how maliciously his ad-

versaries had misinterpreted it while it was still in manuscript. Having

decided to publish the book, Kepler proceeded

the 223 explanatory Notes

mentioned

above, which

to add

are almost

three times as long as the whole text of the Dream proper. In his heading over the Notes Kepler says that they were “writ-

ten in order between the years 1620 and 1630.” As the initial year, however, “1620” must be regarded as a convenient approximation

rather than as a precise determination. The trouble which Kepler recalls in his Note 8 was the legal prosecution of his mother on

charges of witchcraft. The poor old woman was saved from being put to death, in all probability, only by the steadfast and skillful

intervention of her devoted son, the Imperial Mathematician. Hav-

ing obtained his mother’s acquittal, Kepler went home where

he was then living, in November,

friend, Matthias Bernegger

1621.

He

to Linz,

wrote

to his

(1582-1640), on December 4, 1623:

“Two years ago, as soon as I returned to Linz, I began to recast my

Lunar Astronomy, or rather to clarify it by means of notes.” 7 Ac-

cording to this statement, then, Kepler started to write the Notes late in 1621, not in 1620. But there are excellent reasons for believing that he felt more inclined to work on the Notes only after the death of his mother on

April 13, 1622.8 In his Note 8 he speaks of “last year’s journey,” undertaken on his mother’s behalf. Although he began this journey in the closing months of 1620, he himself says about 1621, “I spent the whole

year on my

mother’s

7. Gesam. Werke, XVIII, 143:9-10. 8. Ibid., 212:572. 9. Frisch, VIII, 878:20.

trial.” ® Hence

the reference

in

XX

Introduction

Note 8 to “last year" applies to 1621. Accordingly we shall not be far wrong if we conclude that Kepler actually commenced the Notes in 1622 (or at the very earliest, late in 1621) rather than in 1620, the initial year given in the heading over the Notes. The terminal year, 1630, given in the heading, stands on an entirely different footing, since the heading itself was probably composed in that very same year. On April 22, 163o, Kepler wrote from Zagan, where he then had his own printing press, to his friend Philip Müller: “My employees were hampered by my ab-

sence. Therefore, instead of the Ephernerides

[for which Kepler

evidently had to be present in person on account of the greater complexities involved], they printed the Lunar Astronomy, together with the Notes. There are six sheets already." ^ Kepler's absence from Zagan, to which he here refers, was caused by a trip

lasting perhaps a month, from early March to early April, 1630. His

characteristic habit of constantly introducing changes in his handwritten material '! makes it entirely credible that the closing Notes

were really written in 1630. At any rate, in Note 179 Kepler mentions his Reply to Jacob Bartsch’s Letter, a work which he composed late in 1628 and published early in 1629.

If we now glance back briefly over what has already been said, we see that our book was written in three very different periods of Kepler's life. When he was a student at Tübingen, he composed a

dissertation about the moon in 1593. In 1609, when he was engaged in playful astronomical altercations at Prague, he added the Dream framework. Between 1622 and 1630, years darkened by somber tragedy, both personal and national, he drafted the Notes. In 1623,

he wrote a letter which he later used as the Geographical Appendix to the Dreamz, his Notes on the Geographical Appendix were apparently composed after he moved to Silesia in 1628. In the final version of the Dreamz, therefore, we have a document in which, as

though it were his swan song, Kepler reviewed the various phases

of his long and turbulent life, and the successive stages in his intellectual development. Nowhere else in such brief compass is to be

found Kepler’s own account of his stormy career, one of the main

pathways leading to that awesome force which is modern science.

When

textbook

Bernegger requested him to recommend suitable

for use in the

10. Gesam. Werke, XVIII, 429:23-25. r1. Frisch, VIII, 930:13-12 up.

classroom,

Kepler

a mathematics mentioned

a

Introduction

xxi

number of possible choices, and then asked:

“But what if I added,

as a jest, my ‘Astronomy of the Moon or of the Celestial Phenomena as Seen from the Moon’? This will provide the fare for us who are being chased off the earth [by the Catholic CounterReformation] as we travel or migrate to the moon. To that little book I am appending Plutarch’s Face in the Moon, newly translated [from the Greek] by me.” '? Kepler made these poignant

remarks on March 2, 1629. His were Written in 1630, since in futed an error “26 years ago in On October 8, 1630, Kepler trip. “In the meantime,” we Bartsch,

“he

left me

Notes on his translation of Plutarch one of them he said that he had remy Optics” of 1604." departed from Zagan on a business are told by his son-in-law, Jacob

as supervisor

and

director

of the

printing

operation at Zagan. In accordance with his instructions and with me in charge . . . the major part of his Lunar Astronomy was

printed. He

had conceived it long before, and prior to his depar-

ture he proofread and enlarged it. On account of the unorthodox speculations included in it, he called it his astronomical Dream. Before [the printing of] it was finished down to the very last word, that greatest of men, who devoted himself to the study of the heavens with a zeal that was virtually miraculous, fell into his very last sleep. . . . In the belief that it would be criminal if the work which had been begun was destroyed, I continued to put . . . the Dream through the press." !* How much of the Dreamz was Bartsch able to put through the press? By April 22, 1630, Kepler reported, six sheets of the Dream

were printed. By October 8, 1630, he had corrected the proofs and added something to the Dream, presumably the Geographical Ap-

pendix. After Kepler’s death on November 5/15, 1630, Bartsch fin-

ished putting through the press what had been set up in type. This

did not, however, constitute the complete book. Nevertheless, the bulk of the Dream was ready to be shown to

interested persons. Thus on May 5, 1631, Bartsch wrote from Luban, his birthplace, to Philip Müller (1585-1659), Kepler's friend and Bartsch's former professor of astronomy at Leipzig University:

12. Gesam. Werke, XVIII, 386:45-49. 13. 1634 Somnium, p. 124; Frisch, VIII, 107:9-10. 14. Ibid., VII, 439:23-16 up; 440:11-10 up. For Bartsch’s relationship to Kepler, see Appendix A.

XX11

Introduction

I left a copy brother

at the

of the Dreamz

at Luban

to be sent to Leipzig by my

earliest safe opportunity..

He

said

that

there

had

been opportunities twice, but he heard about them only after he returned from his trips. For on account of his business he has been away

from home quite often. . . . Had I not left that one copy at Luban

then, and were it not here with me now, I would still be unable to send you a copy. For I found that all the other copies had been left

behind at Zagan in a little box amid that very confusing

disorder

[caused by the war], while here at Luban I looked for them in vain among the other books. Through my brother, then, you will receive a copy which has lost its freshness through being read by many people here. l'll send you another copy on cleaner paper soon. I have not yet been able to add the title page and dedication.” 13

Then on June 19/29, 1631, Bartsch professor: “You will receive a copy paper . . . from my brother." !! On asked Müller to have this cleaner copy a publishing and bookselling firm "for mate.

. . . Pll deliver a replacement

again promised the Leipzig of the Dream on cleaner September 3, 1631, Bartsch of the Drear forwarded to an examination and an esticopy

of the Dream

on an-

other occasion." 17 Whether Bartsch lived long enough to fulfill his pledge 1s not known, since he was carried off by the plague not

long thereafter.

On the last day of 1631 Giovanni Pieroni, the Imperial. Archi-

tect, wrote to Galileo from Vienna:

you

Kepler's

posthumous

"I would

book . . . the

by now

'Astronomical

have sent

Dream,

that 1s, the Astronomy of the Moon.’ But on account of the troubles in the region where it was printed, I haven't yet been able to receive it from his son-in-law, Bartsch. However, I did see it before the printing was finished, and it seems strange and bizarre to me. Nevertheless, if it hasn't yet come into your hands, I'll send it to

you, for I still hope to get it.” !? However, Galileo never saw Kep-

ler's Dreanı, so far as we know.

In 1634 Ludwig Kepler, son of Johannes Kepler and his first Wife,? was in Frankfurt/Main. He tells us: “. . . for two years I 15. 16. 17. 18. 19.

Nova Kepleriana, 4, 101:18-31. Ibid., 104:last line. Ibid., 105:16-19. Galileo, Opere, XIV, 323:16-22. Barbara Müller, twice widowed, married

Johannes Kepler

as her third

hus-

band on April 27, 1597. Of the five children born of this marriage, only two sur-

vived their childhood, Ludwig and his older sister Susanna. Their mother died on July 3, 1611 (Caspar, Kepler, tr. and ed. Hellman, pp. 71-77, 174, 202, 206; Frisch,

VIII, 795:22-20 up).

Introduction

had

heard

no

news

about

the condition

xxill

of my

relatives.

From

Frankfurt I wrote to them in Lusatia to let me know whether they

were still alive and how they were faring. Lo and behold, my step-

mother,” an impoverished widow with four orphans,?! comes to me at a turbulent time and in a place most inconvenient on account of the high cost of living.? She brings with her the unfinished

copies of the Dream, and asks for my help. . . . In particular she wants me to complete the copies of this Dream.

. . . I could not

refuse this request, but instead I have made it my goal." ?? Through

the efforts of a son striving to enhance his deceased father's reputa-

tion, Kepler's Dream, having acquired the requisite title page and dedication at Frankfurt, was finally published as a complete book

In 1634.74 To

Galileo’s correspondent,

Giovanni

Pieroni, we

may

recall,

Kepler’s Dream seemed “strange and bizarre.” A biographer of Kepler considered it a satire (presumably on the basis of Kepler’s

Note 56 on the Dream).

Such reactions explain why the Latin

text has been reprinted only once, and why even partial translations were so long delayed. Ihe Dream was not the only book in which Kepler covered his contributions to science with unconventional wrappings repulsive to many readers. But the greatest minds

of the succeeding generations tore these wrappings apart and benefited from Kepler's discoveries. In those days acknowledgment of

such indebtedness was not the universal practice. To track down the influence of Kepler's Dream on the soaring scientific advances

of the later seventeenth century would throw added light on the tortuous process by which the modern mind came into being. 20. Susanna Reuttinger became Ludwig Kepler's stepmother by marrying Johannes Kepler as his second wife on October 3o, 1613 (Caspar, Kepler, tr. and ed. Hellman, p. 222; Frisch, VIII, 809:6-7).

21. Of the children born to Johannes Kepler and his second wife, only four

survived their father's death in 1630.

22. The prices of many common commodities and the wages of certain catego-

ries of workers, in southern Moravia, mainly during the years 1627-1633—midway in the Thirty Years? War—have been extracted from material in the archives at Krumlov (Kromau) by Erich Sloschek, “Lebensmittelpreise während des Dreissig-

jährigen Krieges,” Deutscher Verein für die Geschichte Mährens und Schlesiens, Leitschrift (1935), 37:161-63. 23. Ludwig Kepler’s Dedication to Johannes Kepler’s Dream.

24. Before

the Dream

was

completed

by

Ludwig

Kepler,

some

incomplete

copies were circulated. These lacked the title page and dedication, which Bartsch had not been able to add (Nova Kepleriana, 4, 101:14 up). 25. Johann Ludwig Christian Freiherr von Breitschwert, Johann Keppler’s Leben und Wirken (Stuttgart, 1831), p. 174.

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LUNAR

MATHEMATICIAN

PUBLISHED LUDWIG

ON

AUTHOR'S

1634

AT

IN THE

HEIRS

SILESIA EXPENSE

OF

and

To

the Most

Most

Exalted

PHILIP,

Illustrious Prince

LANDGRAVE

and Lord

OF

HESSE *

Count of Katzenellenbogen, Dietz, Ziegenhain, and Nidda,

To

his Most

Clement

etc.

etc., Lord

and Prince.

Most Illustrious and Most Exalted Prince, Most Clement Lord, when my father, Johannes Kepler, the Imperial Mathematician, was thoroughly exhausted by the motion of the massive earth, he began to dream about the astronomy and movement of the moon. But I do not know what omen this dream brought with it. To us, his children, it certainly was very mournful, although for him the outcome of this omen was pleasant enough, even greatly desired. For when this Dream was written and in press, my father fell into a

sleep (alas!) that was heavy, or rather fatal. His soul flew above the lunar to the ethereal region (we hope) and left us, his children,

not only exposed to the wounds of war and the miseries of this life but almost destitute of all worldly wealth.? The task of printing 1. Philip

III

(1581-1643),

Landgrave

of Hesse,

is also

called

Philip

of Hesse-

Butzbach. His career, as revealed by previously unpublished archival documents, has been studied in a monograph by the court Librarian, Philipp Alexander Ferdi-

nand Walther

(1812-87), in Arch.

f. hess. Gesch.

u. Alt., 11:269-403.

2. Kepler died while he was on a trip undertaken in an unsuccessful effort to collect the interest due him on two promissory notes, which he held in exchange for money that he had deposited at 6 per cent interest in the Treasury of the Estates of Upper Austria.

6

The

Dream

the Dream was undertaken by Jacob Bartsch, M.D., my very famous and learned brother-in-law, who was appointed professor of mathematics at the University of Strasbourg. But he too was stricken by a fatal disease and died before the work was finished. In the meantime I returned to Germany from a trip which I had taken with a certain Austrian baron.’ For two years I had heard no news about the condition of my relatives. From Frankfurt I wrote to them in Lusatia to let me know whether they were still alive and how they were faring. Lo and behold, my stepmother, an impoverished widow with four orphans, comes to me at a turbulent

time and in a place most inconvenient on account of the high cost of living. She brings with her the unfinished copies of this Dreaz, and asks for my help. But I myself need the aid and support of others. In particular she wants me to complete the copies of this

Dream. But what good can I hope for from this Dream, which proved fatal to my father and my brother-in-law? * Yet a son should not hide his father's famous and honored name. If he cannot 3. Johann Joachim von Sinzendorf Wappenbucb, Band 4, Heft 5, p. 369).

(Hansch,

Epistolae,

p. xxxiii

Siebmacber's

4. This question was undoubtedly intended as a kind of macabre jest. Yet it was taken literally by at least one reader, who must have overlooked Ludwig Kepler's

previous statement that, like his father, his brother-in-law, too, was stricken

by a

fatal disease. On June 19, 1677, Gerard de Vries (1648-1705), professor of philosophy and theology at Utrecht University, delivered a lecture on moon-dwellers, in which

he said:

“[The

Dream]

was

Kepler's

last work

on

earth,

and

before

he

could publish it, he himself was shrouded in perpetual darkness. Kepler's son-inlaw, Jacob

Bartsch, a most

fervent supporter

of his father-in-law's

opinions,

had

scarcely undertaken to continue the publication when he, too, was swept away by death. . . . Since

these

developments

widow

with children, and

son, he could scarcely be convinced burdened

were

familiar to Ludwig

Kepler,

Johannes'

by the appeals of his stepmother,

by his regard

a poor

for his father's reputation,

to

lift a finger to complete the printing of the book, which had been begun. He was frightened (as he himself admits) by the unexpected death of his father and brother-in-law, and he was afraid that, together with them, he would

be banished

to the moon.” The foregoing passage was printed by De Vries when he added his own Dissertatio de lunicolis to his edition of Daniel Voet's Physiology (ed. Utrecht, 1678, pp. 268-69; ed. Utrecht, 1688, pp. 253-54).

De Vries’ comments about Ludwig Kepler's fear that if he undertook to finish

the printing of the Dream, it would

finish him, would

undoubtedly

have attracted

less attention had they not been repeated by a widely read author who enjoyed an immense reputation. Pierre Bayle (1647-1706) took De Vries quite seriously in the

article

on

Johannes

Kepler

in his famous

Dictionaire

historique

et critique

(Rotterdam, 1697, II, 231-32). By passing through many editions in the original French as well as in translation, Bayle’s Historical and Critical Dictionary broadcast De Vries’ aspersions on Ludwig Kepler very widely.

The Dream

7

enhance this reputation by his own talent, he should nevertheless preserve it to the best of his ability. Hence I could not refuse this request, but instead I have made it my goal.’

Yet a patron is still lacking for this work. Surely one will hardly

be found among the military. They are now little interested in the

astronomy of the lunar ball, being rather compelled to watch out lest they be blown to bits or injured by musketballs and cannonballs. ‘Therefore I could find no one worthier than you, Most Illustrious Prince, whose patronage this work might enjoy. You are

highly proficient in the study of mathematics;* you are far re-

5. This expression of Ludwig Kepler’s attitude was correctly emphasized by Abraham Gotthelf Kastner (1719-1800), the historian of mathematics and poet, as the effective answer to De Vries (Geschichte der Mathematik, Gottingen, 17961800, IV, 307). 6. 'The proficiency attained by Philip of Hesse-Butzbach in mathematical studies

may

be seen in the letter which

(Gesam.

Werke, XVIII,

ical observations to the wanted Kepler's advice and less labor. In his Landgrave easier ways

the Landgrave

sent to Kepler

in June,

1623

130-31). 'The Landgrave was eager to raise his astronom-

level of accuracy claimed by Tycho Brahe: 3"-;". Philip also in solving spherical triangles with greater precision reply Kepler recalled that he had previously shown the of computing, as well as the difficulties hindering the per-

fection of observational instruments (Gesam. Werke, XVIII, 148:13-23). In his Note 179 on the Dream, Kepler referred to the Landgrave’s sunspot observations, which he described in another work (see fn. 303 on Kepler’s Note 179). Kepler transferred these observations from a flat surface to a three-dimensional sphere when he visited Butzbach, October 6-19, 1627 (Walther, Arch. f. bess. Gesch. u. Alt., 11:369; Frisch, VIII, 909:27-28). In his Admonition to Astronomers Concerning the Rare and Remarkable Phenomena of the Year 1631 (Leipzig, 1629; Frankfurt/Main, 1630), Kepler called attention to the chromatic aberration produced by the lenses in telescopes used for observing sunspots, and then addressed the Landgrave as follows: “Your simple tube without lenses will, I am sure, not be idle. It 1s

so constructed that on its white screen it can show this round

spot’s diameter

quite conveniently measurable even with a pair of compasses. Then, if to this measurement is applied the diameter of the aperture through which the sun’s rays are admitted, the result will be absolutely correct and free from the distortion which is caused by the lower concave lens in a telescope" (Frisch, VII, 594:1016).

The Landgrave was not concerned exclusively with celestial problems. In the spring of 1625, for example, he transmitted to the Tubingen professor Wilhelm Schickard (1592-1635) a “Roman foot” which had been brought from Rome, “and he indicated that there it was regarded as the true ancient” measure (Epistolae W. Schickarti et M. Berneggeri mutuae, p. 43). Feeling that the procedures

of land-surveyors were

erroneous in some

respects, the Landgrave

published

a

Highly Necessary and Basic Reform of Some Harmful Errors Which Have Gradually Crept into tbe General Practice of Land Surveying (Hochnötige unnd gründliche Reformation etlicher in gemeinem ublichem Feldmessen nach und nach eingeschliechener schädlicher Irrtbumbe, Giessen, 1625).

8

The

Dream

moved from the turmoil of war;7 and you favored my father, while he was still alive, with your very kind patronage." Hence the orphans, with firm faith, trust that you will not deny your patronage to them and to this work.” Through me they humbly commend themselves and this Dream to your Most Illustrious Highness. With most zealous prayers they beseech almighty God graciously to deign to preserve your Most Illustrious Highness, together with your Most Illustrious Spouse," sound in body and mind, and to avert every hostile attack and military molestation from your domain. 7. Although Philip of Hesse-Butzbach tried valiantly to safeguard his realm from the horrors of war, the damage actually inflicted is vividly exemplified in the report printed by Walther, Arch. f. bess. Gesch. u. Alt., 11:359-61. 8. In a discussion with the Landgrave, Kepler must have communicated hıs en-

thusiasm for logarithms, which had recently been invented, and he presented his

own ideas on the subject

his Thousand Logarithms

(Gesam.

Werke, XVIII,

(Marburg,

131:38-39). Then, in dedicating

1624) to Philip, Kepler humorously pointed

out in a punning poem that the book’s thirty propositions balanced the Landgrave’s gift to him of thirty pieces of silver (Gresam. Werke, XVIII, 151:145-46; IX, 277, 279:18). Presumably this gift was one of the “benefactions” which Kepler had received from Philip in 1621, and which he recalled six years later in a letter addressed to Philip's nephew, George II, Landgrave of Hesse-Darmstadt (Gesam.

Werke, XVIII, 323:44-45). Philip gave Kepler fifty more silver Reichstalers in gratitude for the dedication, and suggested that Kepler should explain how to use the logarithms (Gesam. Werke, XVIII, 214:11-14; Walther, Arch. f. bess. Gesch.

u. Alt., 11:370-71). This explanation, Kepler's Supplement to tbe Thousand Logaritbms (Marburg, 1625), was likewise published at the expense of the Landgrave, to whom it was dedicated (Gesam. Werke, XVIII, No. 1006:18-27; IX, 353). In 1629 Kepler "extolled the truly generous prince and the bountifulness with which he far overcame the harshness of these times and my original reluctance. I must

say something also about my plans for moving my home. The press at Linz had been destroyed by fire as a result of the peasant uprising, and the printer had been

ruined. lishing as well dence

I was looking around for another location that would be suitable for pubBrahe's observations. It would have to be equipped with presses and type, as remote from the anxieties of the imperial court, moving from one resito another. That same most exalted prince Philip elicited from his nephew

George, the ruler of Darmstadt, a most liberal promise of a place to stay and appropriate subsidies, if the imperial court salary payments were delayed in reaching me there

on account

of my

prolonged

"decided to seek a leave of absence Werke, XVIII, 320:13-14).

absence"

from

(Frisch,

the court

VII,

for two

582:9-18).

years"

Kepler

(Gesam.

9. There is no evidence that Philip of Hesse-Butzbach extended his patronage to the Dream. Pointing in the opposite direction is Ludwig Kepler's statement on the title page that the work was "printed . . . at the expense of the author's heirs." 10. After the death of his first wife, Philip of Hesse-Butzbach married Christina Sophia, marchioness of East Friesland, on June 2, 1632 (Walther, Arch. f. bess.

Gesch. u. Alt., 11:307-10).

The Dream May you accordingly, God and country.

Most

Exalted

9 Prince,

flourish

long

for

Frankfurt/Main,

September 18," 1634

Your Most Illustrious Highness’s most devoted servant, LUDWIG KEPLER, M.A. Candidate for the Doctorate in Medicine.

11. This number, which was poorly printed in the 1634 Somnium (see Günther, Traum, p. 2), was read as “8” by Frisch (VIII, 29:5 up) and as "18" by Caspar

(Bibliographia Kepleriana, p. 107). The later date is undoubtedly correct, as may be seen in the copy at Smith College, Northampton, Massachusetts, which kindly sent me a xerox duplicate of the page in question.

JOHANNES

KEPLER’S

DREAM OR

In the year

LUNAR

ASTRONOMY

1608 there was a heated quarrel between

the Em-

peror Rudolph ” and his brother, the Archduke Matthias.!? Their

actions universally recalled precedents found in Bohemian history. Stimulated by the widespread public interest, I turned my attention to reading about Bohemia, and came upon the story of

the heroine Libussa,'* renowned for her skill in magic. It happened

one night that after watching the stars and the moon, I went to bed and fell into a very deep sleep. In my sleep I seemed to be reading a book brought from the fair. Its contents were as follows. My

name is Duracotus

(1). My

country 1s Iceland

(2), which

the ancients called Thule.» My mother was Fiolxhilde (3). Her

recent death freed me to write (4), as I had long wished to do. While she lived, she carefully kept me from writing (5). For, she 12. Rudolph II (1552-1612), Holy Roman Emperor. 13. Matthias, archduke of Austria (1557-1619).

14. Just as the rule of the Emperor

Rudolph

was challenged by his younger

brother Matthias, so Libussa, a female ruler of the Bohemians, faced an uprising by

males. This tale was lovingly told and retold by narrators of that people's history. Yet it is tempting to think that Kepler “came upon the story of the heroine Libussa," third ruler of the Bohemian people, at pp. 4-7 in the first complete edi-

tion (Hanau, 1607) of the Bohemian Chronicle by the earliest Czech historian, Cosmas of Prague (d. 1125). This edition was published by the same firm that had

brought out Kepler's Optics three years Kepler's interest in Bohemian history In 1604 he had analyzed an event in the denied that it was foreshadowed by a

398:35-399:8).

earlier at Frankfurt. was not aroused for the first time in 1608. political history of medieval Bohemia, and supposed nova of 1284 (Gesam. Werke, I,

15. This unqualified identification of ancient Thule with Iceland was later modified by Kepler: “Scholars deny that our Iceland is ancient Thule, but they point

either to the Shetlands or to Telemark, a district in Norway" p. 169; Frisch, VIII, 119: 12-11 up). II

(Somnium,

1634 ed.,

12

The

Dream

said, the arts are loathed by many vicious people (6) who malign what their dull minds fail to understand, and make laws harmful to mankind (7). Condemned by these laws, not a few persons (8)

have perished in the chasms of Hekla (9). My mother never told me my father’s name

(10). But she said he was a fisherman who

died at the ripe old age of 150 (when I was three) in about the sev-

entieth year of his marriage (11). In the earliest years of my boyhood my mother, leading me by the hand and sometimes hoisting me up on her shoulders, often used to take me up to the lower slopes of Mt. Hekla (12). These

excursions were made especially around St. John’s Day, when the

sun is visible all twenty-four hours, and there is no night (13). Gathering some herbs with many rites, she cooked them at home

(14). She made little bags out of goatskin, which she filled and carried to a nearby port to sell to the ship captains (15). This is how

she earned her living. Once, out of curiosity, I cut a bag open. Suspecting nothing, my mother was about to sell it, when out fell the herbs and linen cloth

embroidered with various symbols

(16). Because I had deprived

her of this little income, she angrily made me, instead of the bag, the property of the skipper in order to keep the money. On the next day he unexpectedly sailed out of the harbor, and with a favorable wind steered approximately toward Bergen in Norway (17). After a few days a north wind sprang up (18) and drove the ship between Norway and England. He headed for Denmark and

passed through the strait, since he had to deliver a letter from a bishop in Iceland to the Dane, Tycho Brahe (19), who lived on the

island of Hven. The tossing of the boat and the unaccustomed warmth of the air (20) made me violently sick, for I was a youth of fourteen. When the boat reached shore, he put me and the letter

in the hands of an island fisherman (21). Expressing the hope that he would return, he sailed away.

When I delivered the letter, Brahe was quite delighted and began to ask me many questions (22).!9 These I did not understand,

since I was unacquainted with the language except for a few words

(23). He therefore instructed his students, whom he supported in

great numbers 16. This Note 2).

(24), to talk to me frequently.

number

was inadvertently

omitted

So it came

in the Sommizan

about,

(1634 ed., p.

The Dream

13

through Brahe's generosity (25) and a few weeks’ practice, that I spoke Danish tolerably well. I was no less ready to talk than they

were to ask. For I marveled at many unfamiliar things, and they wondered about the many novelties I related about my country. Finally the skipper returned to take me back. When he failed, I was very happy (26). I was delighted beyond measure by the astronomical activities,

for Brahe and his students watched the moon and the stars all night with marvelous instruments (27). This practice reminded me of

my mother, because she, too, used to commune with the moon constantly (28). Through this opportunity, then, I, who had come from an entirely destitute background in a half-savage country, acquired knowledge of the most divine science, and this knowledge paved

my way to greater things.

For, after spending several years on this island, I was finally overcome by a desire to see my country again. I considered that it would not be hard for me, with the knowledge I had acquired, to

rise to some position of importance among my backward people.

Hence,

having paid my

respects to my

patron, who

permission to depart, I went to Copenhagen.

gave me his

I found

traveling

companions, who gladly took me under their protection because of my familiarity with the language and the region. Five years after I had left, I returned to my native land. What delighted me first on my return was to find my mother still active and engaged in the very same pursuits as before. The fact that I was alive and important put an end to her prolonged

grief over the son she had lost through her impetuosity. At that

time autumn was approaching (29), to be followed by those long nights of ours, since during the month in which Christ was born

the sun barely rises at noon and sets again at once

(30). On ac-

count of this interruption in her work my mother clung to me and did not leave my side, no matter where I went with my letter of recommendation. Sometimes she asked about the countries which I had visited, and sometimes about the heavens. She was deliriously happy that I had become acquainted with that science. Comparing

what she had learned with my remarks (31), she exclaimed that now she was ready to die, since she was leaving behind a son who would inherit her knowledge, the only thing she possessed (32).

14

The Dream Since I am by nature most eager to acquire new knowledge, I, in

turn, questioned her about her arts and her teachers of those arts

among a people so remote from all the others. Then one day,

choosing the time for her narrative, she went over the whole story from the very beginning, about as follows:

Advantages have been conferred, Duracotus my on all those other regions to which you went but also try, too. To be sure, we are burdened with cold and other discomforts, which I feel only now, after I have you about the salubriousness of the other lands.

son, not only on our coundarkness and learned from But we have

plenty of clever persons (33). At our service are very wise spirits (34.), who detest the bright light of the other lands and their noisy

people. They long for our shadows, and they talk to us intimately. Among them there are nine chief spirits (35). Of these, one is especially well known to me (36). The very gentlest and most innocuous of all (37), he is evoked by one and twenty characters (38). By his help I am not infrequently whisked in an instant to other shores (39), whichever I mention to him; or if I am frightened

away from some of them on account of their distance (40), by in-

quiring about them I gain as much as if I were there in person (41).

Most of the things which you saw with your own eyes or learned by hearsay or absorbed from books, he related to me just as you did. I should like you to become my companion on a visit, particularly, to that region of which he has spoken to me so often. Quite remarkable are the things which he tells about it. The name she

uttered was "Levania" (42).

Without any delay I agreed that she should summon I sat down, ready to hear the entire plan for the trip tion of the region. It was already spring. The moon, crescent, began to shine as soon as the sun set below

her teacher. and descripbecoming a the horizon,

and was in conjunction with the planet Saturn in the sign of the Bull (43). My mother went away from me (44) to the nearest crossroads (45). Raising a shout, she pronounced just a few words (46) 1n which she couched her request. Having completed the

ceremonies, she returned (47). With the outstretched palm of her right hand she commanded silence, and sat down beside me (48). Hardly had we covered our heads with our clothing (49) (in accordance with our covenant) when the rasping of an indistinct

The

Dream

-

and unclear voice became audible (50). It began at once as follows, albeit in the Icelandic tongue.

Tbe

Daemon

($1)

from

Levania

(52)

Fifty thousand German miles (53) up in the ether lies (54) the

island of Levania. The road to it from here or from it to this earth is seldom open (55). When it is open, it is easy for our kind (56),

but for transporting men it is assuredly most difficult and fraught with the greatest danger to life (57). We admit to this company

nobody who is lethargic, fat, or choose those who spend their horsemanship or often sail to hardtack, garlic, dried fish, and

tender (58).!* On the contrary, we time in the constant practice of the Indies, inured to subsisting on unappetizing victuals (59). We es-

pecially like dried-up old women (60), experienced from an early age in riding he-goats at night or forked sticks or threadbare cloaks, and in traversing immense

expanses of the earth. No

men

from Germany are acceptable; we do not spurn the firm bodies of

Spaniards (61). Great as the distance is, the entire trip is consummated in four hours at the most (62). For we are always very busy, and agree

not to start (63) until the moon begins to be eclipsed on its eastern

side.*® Should it regain its full light while we are still in transit, our

departure becomes futile. Because the opportunity is so fleeting, we

take few human

beings along, and only those who

are most

de-

voted to us (64). Some man of this kind, then, we seize as a group and all of us, pushing from underneath, lift him up into the heavens

17. The preferred body type would be thin, made so by constant physical exercise or by a lean diet. The autobiographical reference is unmistakable, even though Kepler once described himself as “like a tender household puppy.” For he

went on at once to say that his “body is agile, dry, and well proportioned. His diet

is certainly just like that, for he loves to gnaw on bones and hard bread crusts.

. . . He drinks little, and is satisfied even with the cheapest foods" (Frisch, V, 483:3-6). “I enjoy the taste of bitter and sour things. I take pleasure in walking over rough ground, up hills, and through thickets. Apart from my studies, I neither have nor desire the spices of life, and when they are offered to me, I reject them," he told his patron, Herwart von Hohenburg, the Chancellor of Bavaria (Gesam. Werke, XIII, 311:257-60; cf. XVII, 86:258). 18. The very busy daemons remind us of Kepler's remark that "he was annoyed at the waste of the smallest amount of time" (Frisch, V, 477:26 up).

16

The

Dream

(65). In every instance the take-off hits him as a severe shock (66), for he is hurled just as though he had been shot aloft by gunpowder to sail over mountains and seas (67). For this reason at the

outset he must be lulled to sleep immediately with narcotics and opiates (68). His limbs must be arranged (69) in such a way that his torso will not be torn away from his buttocks nor his head from his body, but the shock will be distributed among his individual

limbs. Then a new difficulty follows: extreme cold (70) and impeded breathing (71). The cold is relieved by a power which we are born with

(72); the breathing, by applying damp

sponges to

the nostrils (73). After the first stage of the trip is finished, the pas-

sage becomes easier (74). At that time we expose their bodies to

the open air and remove our hands (75). Their bodies roll themselves up, like spiders, into balls which we carry along almost entirely by our will alone (76),” so that finally the bodily mass pro-

ceeds toward its destination of its own

accord

(77).” But this

onward drive is of very little use to us, because it is too late (78). Hence it is by our will, as I said, that we move the body swiftly along, and we forge ahead of it from now on lest it suffer any harm

by colliding very hard with the moon. When the humans wake up,

they usually complain about an indescribable weariness of all their

limbs, from which they later recover well enough to walk (79).

Many additional difficulties arise which it would be tedious to enumerate. On the other hand, we suffer no harm at all. For as a

group we inhabit the earth’s shadows (80), whatever their length.

When they reach Levania, there we are as though disembarking from a ship and going ashore (81). Up there we quickly withdraw into caves and dark places (82), lest after a short while the sun

overpower us in the open, and drive us out of the living quarters we had chosen, and force us to follow the retreating shadow (83). Up there we are granted leisure to exercise our minds in ac-

cordance with our inclinations. We consult with the daemons of that area and enter into a Jeague. As soon as a spot begins to be free

from sun (84), we close ranks and move out into the shadow. If it 19. Kepler's use of stu here and in his Note 76 resembles his use of that word

in the Epitome (Gesam. Werke, VII, 296:27) and in the Cosmographic Mystery (Gesam. Werke, VII, 93:44).

20. For Kepler’s contribution

inertia, see Appendix I.

to the development

second

of the modern

edition

of the

principle of

The Dream

17

touches the earth with its apex, as generally happens (85), we rush

toward the earth with our allied forces.?' This we are permitted to do only when mankind sees the sun in eclipse. Hence it happens that solar eclipses are feared so much (86). I have said enough about the trip to Levania. Next I shall talk about the nature of the region itself, starting like the geographers with its view of the heavens.

The fixed stars look the same to all Levania as to us (87). But its

view of the movements

and sizes of the planets is very different

from what we observe here, so that its entire system of astronomy

Is quite diverse.

Just as our geographers divide up the sphere of the earth into

five zones on the basis of celestial phenomena, so Levania consists of two hemispheres (88). One of these, the Subvolva, always enjoys its Volva, which among them takes the place of our moon. The other one, the Privolva (89), 1s deprived forever of the sight

of Volva (90). The circle which separates the hemispheres passes

through the celestial poles, like our solstitial colure, and is called

the divisor (91).

In the first place I shall explain what is common to both hemispheres. All Levania experiences the succession of day and night as

we do (92), but they lack the variation that goes on all year among us (93). For throughout the whole of Levania the days are almost

exactly equal to the nights, except that each day is uniformly shorter than its night for the Privolvans, and for the Subvolvans

longer (94). What varies in a period of eight years will be men-

tioned later on. To produce equal nights at each of the poles, the sun is hidden half the time and shines half the time ?? as it travels

around the mountains ?? in a circle (95). For Levania seems to its

inhabitants to remain just as motionless among the moving stars as

does our earth to us humans

(96). A night and a day, taken to-

gether, equal one of our months, since at sunrise in the morning al-

most an entire additional sign of the zodiac appears on any day as compared with the previous day (97). For us in one year there are 21. These “allied forces" are “the daemons of that area," the moon. :2. As Kepler later explains (p. 18, below), the alternation of summer tcr “is scarcely felt near the equator,” whereas it "is felt much more

and winnear the

poles, where the sun is present or absent in alternating periods of six months."

23. At regular intervals the mountains Kepler's lunar observers.

on the moon

come

between

the sun and

18

The

Dream

365 revolutions of the sun, and 366 of the sphere of the fixed stars,

or more accurately, in four years, 1461 revolutions of the sun but

1465 of the sphere of the fixed stars. Similarly, for them the sun revolves 12 times in one year and the sphere of the fixed stars 13 times, or more precisely, in eight years the sun revolves 99 times and the sphere of the fixed stars 107 times. But they are more famil-

iar with the nineteen-year cycle, for in that interval the sun rises

235 times, but the fixed stars 254 times (98). The

sun rises for the middle

or central Subvolvans

when

the

moon appears to us in its last quarter,?* but for the middle Privolvans when we have the first quarter. What I say about the middle must be understood as applying to complete semicircles drawn through the poles and the middle at right angles to the divisor.

These may be called the Midvolvan semicircles (99).

Halfway between the poles there is a circle corresponding to our terrestrial equator, by which name it too may be denoted. It twice intersects both the divisor and the Midvolva in opposite points. At all places on the equator the sun at noon passes almost exactly overhead daily, and exactly overhead on two opposite days of the year. For all the others, who live on either side of the equator toward the poles, the sun deviates from the zenith at noon (100). On Levania.they have also some alternation of summer and winter. But the contrast is not to be compared with ours, nor does it always occur, as with us, in the same places at the same time of year. For within a period of ten years their summer shifts from one part of the sidereal year to the opposite part in any given place.

The reason is that in a cycle of nineteen sidereal years, or 235

Levanian days, summer occurs winter just as often, but forty year they * have six summer months (102). This alternation

twenty times near the poles and times at the cquator (101). Every days, the others winter, like our is scarcely felt near the equator,

because in those places the sun deviates no more than 5° back and

24. Exactly the opposite is true: the sun rises for the mid-Subvolvans when the

moon appears to us in its first quarter, not in its last quarter. The mid-Subvolvans believe that the hour is midnight when the moon is new for us (see Kepler's Note 111). Hence for them the sun rises when the moon, as seen from the earth, enters its first quarter. 25. Kepler's illos refers to the moon-dwellers, not to the poles, which have only two days a year, one summer and the other winter, each six months long.

The Dream

19

forth to either side. It is felt much more near the poles, where the sun is present or absent in alternating periods of six months,

as is

the case among us on earth for those who live near either of the poles. Hence the sphere of Levania, too, is divided into five zones,

corresponding somewhat to our terrestrial zones. But their tropical

zone, like their arctic zones, contains scarcely 10°. All the rest belongs to zones similar to our temperate zones (103). The tropical zone passes through the middle of the hemispheres, with half of its

longitude in the Subvolva and the other half in the Privolva.

The intersections of the equatorial and zodiacal circles create four cardinal points, like our equinoxes and solstices. These inter-

sections mark the start of the zodiacal circle (104). But from this start the motion of the fixed stars in the order of the signs is very

swift, since they traverse the entire zodiac in twenty tropical years (a tropical year being defined as one summer and one winter). For us this traversing takes almost 26,000 years (105). So much for the first motion. The theory of the second motions is for them no less different from what appears to us, and is much more complicated for them

than for us. The reason is that all six planets (Saturn, Jupiter, Mars,

sun, Venus, Mercury) exhibit, besides the many inequalities which they have in common with us, three others for them. Two of these irregularities are in longitude; one is daily, the other has a period of eight and a half years. The third is in latitude, with a period of nineteen years. For the mid-Privolvans have the sun at their noon, other things being equal, bigger than when it rises, and the Subvolvans smaller (106). Both agree in believing that the sun diverges by some minutes from the ecliptic back and forth now

among these fixed stars, now among those (107). These oscillations

return to the original position, as I said, in a period of nineteen years. Yet this deviation takes a little more time for the Privolvans,

a little less for the Subvolvans (108). And although the sun and the

fixed stars are assumed to advance uniformly in the first motion around Levania, nevertheless, the sun barely progresses in relation to the fixed stars at noon for the Privolvans, whereas for the Subvolvans it is very fast at noon. The reverse is true at midnight. Hence the sun seems to make, as it were, certain jumps in relation

to the fixed stars, separate jumps every day (109).

20

The

Dream

The same statements hold true for Venus,

Mercury,

and Mars;

in the cases of Jupiter and Saturn, these phenomena are almost ımperceptible (110).

Furthermore the diurnal motion is not uniform even at the same hour every day. On the contrary, it is slower at times not only for the sun but also for all the fixed stars, while at the opposite season of the year at the like hour of the day it is faster (111). Moreover, that retardation shifts throughout the days of the year, so that sometimes it occurs on a summer day, sometimes on a winter day, which in another year had experienced the acceleration, one cycle being completed in a period of a little less than nine years (112). Hence the day sometimes becomes longer (through a natural retardation, not as with us on the earth through the unequal division of the natural day), and sometimes the might, in turn, be-

comcs longer (113)

But if the retardation occurs for the Privolvans during their night, its excess over their day is increased; on the other hand, if the retardation falls in their day time, then their night and day approach more closely to equality, which is reached once in nine

years. The converse is true for the Subvolvans (114).

So much for the phenomena common to the hemispheres.

The Hemisphere

which

in a certain way happen in

of the Privolvans

Now as for what concerns the individual hemispheres separately, there 1s an enormous contrast between them. By its presence and absence Volva gives rise to quite different spectacles. Not only that, but the common phenomena themselves produce very divergent effects on the two sides. As a result, the Privolvans’ hemisphere may perhaps more properly be called non-temperate, and the Subvolvans’, temperate. For among the Privolvans night lasts fifteen or sixteen of our natural days. It is made frightful bv as deep in uninterrupted darkness as we have on a moonless night, since it never receives any light even from Volva’s rays . Consequently evervthing turns stiff with ice and frost (115). abetted by very sharp and very strong winds (116). Day follows, as long as fourteen of our day s or a little less (117). During this time the sun

The

Dream

21

is quite large (118), and moves slowly with respect to the stars (119). There are no winds (120). The result is immense And thus, in the interval of our month or the Levanian day, and the same place is exposed both to heat fifteen times hotter our African, and to cold more unbearable than the Quiviran.??

fixed heat. one than

It should be especially noted that the planet Mars sometimes ap-

pears almost twice as big to the Privolvans as to us (121); to the mid-Privolvans this happens at midnight, and to the other Privol-

vans at some particular moment of the night for each.

The Hemisphere

of the Subvolvans

In making the transition to this topic, I begin with the frontiers-

men who inhabit the divisor circle. What is peculiar to them 1s that the elongations of Venus and Mercury from the sun seem much bigger to them than to us (122). Moreover, at certain times Venus

looks twice as big to them as to us (123), especially to those of them who live near the north pole (124).

But the most beautiful of all the sights on Levania 1s the view of its Volva. This they enjoy to make up for our moon, of which

they and likewise the Privolvans are completely deprived

(125).

From the perennial presence of this Volva this region is termed the Subvolvan, just as from the absence of Volva the other region is called the Privolvan, because they are deprived of the sight of Volva. To us?” who inhabit the earth, our moon, when it is full and rising and climbing above distant houses, seems equal to the rim of

a keg; when it mounts to mid-heaven, it hardly matches the width

of the human face. But to the Subvolvans, their Volva in midheaven (a position which it occupies for those who live in the center or navel of this hemisphere) looks a little less than four times longer in diameter than our moon does to us. Hence, if the disks are compared, their Volva is fifteen times larger than our moon (126). However, to those for whom Volva always clings to the

horizon, it presents the appearance of a mountain on fire far away.

Consequently, just as we differentiate between regions according

26. See Appendix J. | 27. Reading Nobis instead of Notis (1634 Somnium, p. 16).

22

The

Dream

to the greater and smaller altitudes of the pole, even though we do

not see the pole itself with our eyes, so this same function 1s per-

formed for them by Volva, which, although it is always visible, differs in altitude from place to place. For, as I said, Volva stands directly over the heads of some of them; in other places it is seen low down near the horizon; and for the rest its altitude varies from the zenith to the horizon, while re-

maining forever constant in any given area (127). Yet they, too, have their own

poles

(128). These

are located,

not at those fixed stars where our celestial poles are (129), but

around other stars which for us mark the poles of the ecliptic. These poles of the moon-dwellers in a period of nineteen years

traverse small circles around the poles of the ecliptic (130) in the

constellation of the Dragon and, at the other extremity, in the Swordfish (Dorado), Sparrow (Flying Fish), and the Greater Nebula. Since these poles of the moon-dwellers are about a quadrant’s distance from their Volva, their regions can be delimited

both according to the poles and according to Volva (131). Hence

it is clear how much more convenient their situation is than ours. For they indicate the longitude of places with reference to their

motionless Volva

(132), and the latitude with reference both to

Volva and to the poles (133), whereas for longitudes we have nothing but that most lowly and barely perceptible declination of

the magnet (134).

Their Volva remains fixed in place, then, as though it were attached to the heavens with a nail. Above it the other heavenly bodies, including the sun, move from east to west (135). There is never a night in which some of the fixed stars in the zodiac do not

pass behind this Volva and emerge again on the other side (136). But the same fixed stars do not do so every night (137). All those which are within a distance of 6° or 7° from the ecliptic take turns (138). The cycle is completed in nineteen years, after which the first stars return (139).

Their Volva waxes and wanes no less than our moon does (140). In both cases the cause is the same: the presence of the sun or its

departure. The length of time involved is also the same, if you look

to nature. But they measure it in one way, and we in another. They consider a day and a night the interval in which their Volva

The Dream

23

passes through all its waxings and wanings. This is the interval which we call a month. On account of its size and brilliance Volva is practically never, not even at new Volva, hidden from the

Subvolvans (141). This is true in particular for those who live near

the poles and are deprived of the sun during that time. For them Volva turns its horns upward at noon in the inter-Volvan period

(142). For in general, for those who live between Volva?® and

the poles on the mid-Volvan circle, new Volva is the sign of noon;

the first quarter, of evening; full Volva, of midnight; ?? the last quarter, of returning sunlight (143). For those who have Volva as

well as the poles located on the horizon and who live at the inter-

section of the equator with the divisor, morning or evening occurs

at new Volva and full Volva, noon or midnight at the quarters. Let these remarks provide the basis for conclusions regarding those

who live in between (144).

In the daytime, too, they distinguish the hours in this way ac-

cording to the various phases of their Volva; for example,

the

closer the approach of the sun and Volva to each other, the nearer is noon for the mid-Volvans, and evening or sunset for those at the

equator. But at night, which regularly lasts as long as fourteen of our days and nights, they are much better equipped to measure

time than we are. For besides that series of Volva’s phases, of which we said that full Volva is the sign of midnight at the midVolvan circle, Volva itself also distinguishes the hours for them. For even though it does not seem to have any motion in space (145), nevertheless, unlike our moon, it rotates in its place (146)

and displays in turn a wonderful variety of spots, as these spots move constantly from east to west (147). One such revolution, in

which the same spots return (148), 1s regarded by the Subvolvans as one hour of time (149); it is equal, however, to a little more than one of our days added to one of our nights (150). This is the only uniform measure of time (151). For, as was pointed out above;?? the sun and stars move non-uniformly about the moon-dwellers

every day. This non-uniformity is revealed very clearly by this ro28. Here Kepler uses Volva as a compact expression to designate that place on

the moon which has 29. When Volva midnight. See fn. 24, 30. See pp. 19-20,

Volva directly overhead (see Kepler's Note 127). is full, the moon is new, and the mid-Subvolvans above. above.

have

their

24

The Dream

tation of Volva*

if it is compared with the distances of the fixed

stars from the moon (152).

So far as its upper, northern part is concerned, Volva in general

seems to have two halves (153). One of them is darker and covered with almost continuous spots (154). The other is a little lighter

(155), being interpenetrated by a bright belt (156) which lies to the north and serves to distinguish the two halves. In the darker half the shape of the spot is hard to describe. Yet on the eastern side (157) it looks like the front of the human head cut off at the shoulders (158) and leaning forward to kiss a young girl (159) ina long dress (160), who stretches her hand back (161) to attract a leaping cat (162). The bigger and broader part of the spot (163),

however, extends westward (164) without any apparent configuration. In the other half of Volva the brightness is more widely diffused (165) than the spot (166). You might call it the outline of

a bell (167) hanging from a rope (168) and swinging westward (169). What lies above (170) and below (171) ?? cannot be lik-

ened to anything (172).

Besides distinguishing the hours of the day for them in this manner, Volva also furnishes no obscure indication of the seasons of

the year to anyone who is observant, or who is unaware of the arrangement of the fixed stars. Even when the sun is in the sign of the Crab (173), Volva clearly displays the north pole of its rotation. For there is a certain small dark spot

(174)

which

is stuck

(175) in the middle of the bright area above the figure of the girl. From the highest and uppermost part of Volva (176) this spot moves toward the east, and then as it drops down

over the disk,

toward the west (177); from this side it again turns eastward to-

ward the top of Volva, and thus it is perpetually visible at that time

(178). But when the sun is in the sign of the Goat, this spot is nowhere to be seen since the entire circle with its pole disappears behind the body of Volva.

In these two seasons

of the year the

spots travel westward in a straight line (179). But in the interven-

ing seasons, when the sun is in the sign of the Ram * or the Bal-

31. Here Kepler is contrasting the uniformity of the earth's axial rotation with the non-uniformitv of the other celestial motions as observed from the moon. 32. These two numbers (170 and 171) were interchanged in the 1634 Somnium. 33. Ariete, misprinted Oriente in the 1634 Somnium, p. 21.

The Dream

25

ance, the spots either drop down or climb up crosswise in a somewhat crooked line. These facts show us that, while the center of the body of Volva remains stationary, the poles of this rotation revolve on an arctic circle once a year around the pole of the moondwellers (180).*4 More careful observers notice also that Volva does not always retain the same size. For at those hours of the day when the heavenly bodies travel fast, the diameter of Volva is much bigger, so that then it altogether exceeds four times the diameter of our moon (181). What shall I say now about the eclipses of the sun and of Volva? Eclipses occur on Levania too, and they occur at the same moments as solar and lunar eclipses here on the globe of the earth, although obviously for the opposite reasons. For when a total eclipse of the sun is visible to us, for them Volva is eclipsed. In turn, when our moon is eclipsed for us, the sun is eclipsed for them (182). Nevertheless, the correspondence is not complete. For they often see partial eclipses of the sun when no part of the moon is blacked

out for us (183). On the other hand, they not infrequently miss eclipses of Volva when we have partial eclipses of the sun (184).

Volva is eclipsed for them when it is full, just as is the moon for us when it is full; but the sun 1s eclipsed at new Volva, as it is for us at

new moon (185). Since their days and nights are so long, they ex-

perience very frequent darkenings of both bodies. For whereas among us a large percentage of the eclipses passes on to our antipodes, their antipodes, because they are Privolvans, see absolutely none of these phenomena, which are all witnessed by the Subvolvans alone. They never see a total eclipse of Volva (186). However, for

them the body of Volva is traversed by a certain small spot (187)

which

is reddish

around

the rim

(188)

and black in the middle

(189). Entering from the eastern side of Volva, it leaves by the western edge (190), following the same course as the natural spots

of Volva, while surpassing them in speed (191). It lasts one-sixth of

a Levanian hour or four of our hours (192).

A solar eclipse is caused for them by their Volva, just as it is for

34. Kepler's above.

illorum: means

"theirs"

(ie.

of the

moon-dwellers),

as in fn.

25,

26

The

Dream

us by our moon. This phenomenon is inevitable since Volva has a diameter four times bigger than the sun’s.”” As the sun crosses from the east through the south beyond the motionless Volva to the west, it very often passes behind Volva, which thus occults the sun’s body partially or totally. Even though an occultation of the sun’s entire body is frequent, it is nevertheless quite remarkable be-

cause it lasts several of our hours (193), while the light of both the

sun and Volva is extinguished at the same time.?? This is a grand

spectacle for the Subvolvans. For under other circumstances their nights are not much darker than their days on account of the bril-

liance and size of Volva, which is always present, whereas in a solar eclipse both luminaries, the sun and Volva, are quenched for them. Yet among them solar eclipses have the following peculiar feature. Hardly has the sun disappeared behind the body of Volva than, as happens quite frequently, bright light arises on the opposite side. It is as though the sun expanded and embraced the entire body of Volva, whereas at other times the sun appears just as many

degrees smaller than Volva

(194). Therefore complete darkness

does not always occur, unless the centers of the bodies are almost

exactly aligned (195) and the condition of the intervening trans-

parent medium is suitable (196). Nor, on the other hand, is Volva extinguished so suddenly that it cannot be seen at all (197), even though the sun is entirely hidden behind it; the only exception

takes place at the middle moment of a total eclipse (198). But at the beginning of a total eclipse in certain localities on the divisor

Volva still shines, like an ember which continues to glow after a flame has been put out. When Volva, too, ceases to shine, the middle of the total eclipse has arrived (for if the eclipse is not total, Volva does not cease to shine). When Volva resumes its shining (at the opposite localities on the divisor circle) the sun also approaches visibility. Thus to a certain extent both luminaries are ex-

tinguished at the same time in the middle of a total eclipse (199).

So much for the phenomena in both hemispheres of Levania, the Subvolvan and the Privolvan. From these phenomena, even with35. Kepler is comparing, not the actual diameters, but the apparent

diameters as

they would look to an observer on the moon. 36. The light of the sun is extinguished because that body is (apparently) passing behind Volva, which is opaque. Volva’s light is extinguished at the same time because the side then visible to an observer on the moon is turned away from the sun, the source of Volva’s light.

The Dream

27

out my saying anything, it is not difficult to infer how much the

Subvolvans differ from the Privolvans in all other respects.

For although the Subvolvan night lasts as long as fourteen of our

days and nights, nevertheless by its presence Volva lights up the

land and protects it from the cold. Indeed, so huge a mass, so intense a brilliance cannot fail to impart warmth (200). On the other hand, even though a day among the Subvolvans has the sun irksomely present for fifteen or sixteen of our days and nights, nevertheless it is a smaller sun, whose strength is not so dangerous (201). Ihe luminaries, being joined, pull all the water to

that hemisphere (202), where the land is submerged so that only a tiny quantity of it protrudes (203). By contrast the Privolvan

hemisphere is dry and cold because all the water has been drawn off (204). However, when night begins for the Subvolvans and day for the Privolvans, the hemispheres divide the luminaries between them, and therefore the water is divided ? too; the fields of the Subvolvans are drained, whereas the moisture provides the Privolvans with some slight relief from the heat (205). The whole of Levania does not exceed fourteen hundred German miles in circumference, that is, only a quarter of our earth (206). Nevertheless, it has very high mountains (207) as well as very deep and wide valleys (208); to this extent it is much less of a

perfect sphere than our earth is. Yet it is all porous and, so to say,

perforated with caves and grottoes everywhere (209), especially in the Privolvan region (210); these recesses are the inhabitants’ principal protection from heat and cold (211). Whatever 1s born on the land or moves about on the land (212) attains a monstrous size. Growth is very rapid. Everything has a short life, since it develops such an immensely massive body (213). The Privolvans have no fixed abode, no established domicile. In the

course of one of their days they roam in crowds over their whole sphere, each according to his own nature: some use their legs, which far surpass those of our camels; some resort to wings; and some follow the receding water in boats; or if a delay of several more days is necessary, then they crawl into caves. Most of them are divers; all of them, since they live naturally, draw their breath very slowly; hence under water they stay down on the bottom, 37. The misprint dividantur in the Somnium

dividuntur by Frisch (VIII, 38:15 up).

(1634 ed., p. 25) was corrected to

28

The

Dream

helping nature with art (214). For in those very deep layers of the

water, they say, the cold persists while the waves on top are heated up by the sun (215); whatever clings to the surface is boiled out by the sun at noon, and becomes food for the advancing hordes of wandering inhabitants (216). For in general the Subvolvan hemisphere is comparable to our cantons, towns, and gardens; the Privolvan, to our open country, forests, and deserts. Those for whom breathing is more essential introduce the hot water into the caves through a narrow channel in order that it may flow a long time to reach the interior and gradually cool off. There they shut themselves up for the greater part of the day, using the water for drink; when evening comes, they go out looking for food (217).

In plants, the rind; in animals, the skin, or whatever replaces 1t,

takes up the major portion of their bodily mass; it is spongy and porous. If anything ts exposed during the dav, it becomes hard on top and scorched: when evening comes, its husk drops off (218). Things born in the eround—they are sparse on the ridges of the mountains—generally begin and end their lives on the same day, with new generations springing up daily. In general, the serpentine nature is predominant. For in a wonderful manner they expose themselves to the sun at noon as if for pleasure; yet they do so nowhere but behind the mouths of the caves to make sure that they may retreat safely and swiftly (219). To certain of them the breath they exhaust and the life they lose on account of the heat of the day return at night; the pattern is the opposite of that governing flies among us (220). Scattered evervwhere on the ground are objects having the shape of pine cones. Their shells are roasted during the day. In the ev ening when, so N say, they disclose their secrets, they beget living creatures (22 Relief from the heat in the Subvolvan hemisphere IS prov ded chiefly by the constant cloud cover and rain (222), which sometimes prevail over half the region or more (223).

When I had reached this point in my dream, a wind arose with the rattle of rain, disturbing my sleep and at the same time Wiping out the end of the book acquired at Frankfurt. Therefore, leaving behind the Daemon narrator and her auditors, Duracotus the son with his mother, Fiolxhilde, as they were with their heads covered

The Dream up, I returned to myself and found my the pillow ?* and

my

body

29 head really covered with

with the blankets.

38. [his inversion is intended to be a humorous parallel to Duracotus and his mother, who covered their heads with their clothing, and to the observers of the solar eclipse, who covered their heads with their coats (see Kepler’s Note 49).

JOHANNES NOTES

KEPLER’S ON

HIS

ASTRONOMICAL

DREAM

These Notes were written in order between the years 1620 and 1630.

1. The very sound of the word was suggested to me by my

recollection of proper names of similar sound in the history Scotland,’ a country which looks out upon the Icelandic Sea.

of

2. In our German language this means "Ice Land." But in this remote island I perceived a place where I might fall asleep and

dream, in imitation For Cicero crossed dream.? Moreover, lantis, whence he

of the philosophers in this branch of literature. over into Africa when he was getting ready to in the same western ocean Plato fashioned Atsummoned imaginary aids to military valor?

1. For his knowledge of the history of Scotland, like most of his contemporaries, Kepler relied on George Buchanan's Rerum Scoticarum historia (Edinburgh, 1582), as may be seen in Kepler's Note 11. To support the view that pre-Roman Gaul and Britain spoke identical or closely related languages, the renowned Scottish historian, in Bk. II, analyzed place names: "Not a few are derived from ‘dur,’ a word which meant ‘water’ among the ancient Gauls and Britons . . . . In Gaul,

Durocotti . . ." (1582 ed., fol. 23, ll. 67-71). In Buchanan's history of Scotland,

then, Kepler came across the name of this important Gallic town, which was mentioned in Julius Caesar's Gallic War (vi.44), Strabo (iv.194), and Ptolerny’s Geography (ii.9.12, viii.s.6). It was this Gallic place name that suggested “Duracotus” to Kepler.

2. In Bk. vi of his dialogue on the Republic, Cicero portrayed one of his interlocutors as arriving in Africa, where he then proceeded to have the famous

"Dream of Scipio."

3. While successfully repelling an invasion by the armed forces of the fabulous 30

Kepler’s Notes on the Dream

31

Finally, Plutarch, too, in his little book on The Face in the Moon;

after prolonged discussion ventures out into the American ocean and describes to us such an arrangement of islands as a modern geographer would probably apply to the Azores, Greenland, and the territory of Labrador, regions situated around Iceland.5 Every island Atlantis, described by Plato in his Timaeus, 24E-25D, and I08E, 113C-121C, Athens' military prowess rose to a peak. Plato

in his Critias, attributed the

story to an old Egyptian priest, however, not to a dream.

4. The Face in the Moon, the most valuable discussion of the earth’s satellite to

come down to us from antiquity, will be cited hereafter for the sake of brevity as Moon. 5. Kepler's regionibus circum Islandiam sitis is not an addition to the Azores, Greenland,

and

Labrador,

but is in apposition

to those

three

places. They

were

Kepler's candidates to be the modern equivalents of three islands mentioned by

Plutarch, and were turned by him into "regions situated around

he had already selected it as the scene of his Dream.

Iceland," because

What Plutarch characterized as a myth, not a dream, starts with an island "whose distance from Britain is a run of five days as you sail toward the west; at

an equal distance from it and from one another, three other islands extend for the most part in the direction where the sun sets in the summertime” (Moon, g940F941A).

Nevertheless, Plutarch's statement that “he is telling nothing

but a fable"

was ascribed to his modesty by Kepler in Note 97 on his Latin translation of Plutarch's Moon. Moreover, Kepler said, Plutarch's "start and topography, which we find in agreement with the actual facts," are such that "he could hardly have written in this way merely from an unfettered imagination." Had Plutarch designated the Mediterranean area as the starting point of his five-day voyage, Kepler “would have believed him to be talking about the Hesperides or even the Azores. But because he chose Britain, he certainly seems to be referring to Iceland and three islands lying around it." The identification of these three islands baffled Kepler, however, because he believed Plutarch's topography to be "in agreement with the

actual

facts."

Thus,

of the

three

places

named

in

Kepler'

Note

2 on

the

Dream, Labrador was known not to be an island (that is why Kepler called it a

territory), and the Azores lie far south, not northwest, of Iceland. Hence, of the three, only Greenland was kept when Kepler later wrote Note 97 on his transla-

tion of Plutarch's Moon. 'There he coupled with Greenland two other which have since disappeared from our atlases. The geographers on whom lied were the best of his time. But after only a little more than a century ploration of the New World, their knowledge of the recently discovered

islands he reof exlands

was understandably far from accurate. In reality, then, Kepler had no sound basis

for equating Plutarch's "great continent" with the New World. When Kepler spoke of Plutarch “venturing out into the American ocean," he was, of course, using a modern term that had been coined in the previous century to honor Amerigo Vespucci. For an analysis of Kepler's comments on Plutarch's Moon, see

Eduard Ebner, Geographische Hinweise und Anklange in Plutarchs Schrift “De facie in orbe lunae" (Munich, 1906), especially pp. 73-80. A new English transla-

tion of the Moon

Princeton,

was

by

published

Harold in

1957

Cherniss

of the

Institute

as the first piece

for Advanced

in Volume

XII

Study,

of Plutarch’s

Moralia in the Loeb Classical Library. Kepler’s translation of Plutarch’s Moon into

32

Kepler's Notes on the Dream

time I reread this book by Plutarch, I am exceedingly amazed and keep wondering by what chance it happened that our dreams or fables coincided so closely. For with my quite reliable memory I recall the origins of the individual parts of my tale, because they did not all come to me from reading this book. I have a very old document which you, most illustrious Christopher Besold,® wrote

with your own hand, when, in the year 1593, on the basis of my essays,’ you formulated about twenty theses concerning the celestial

phenomena on the moon ? and showed them to Veit Müller, who then regularly presided over the philosophical disputations, with the

thought that you would engage in a debate over them if he approved.? At that time I had not yet seen the works of Plutarch. Later I came across the two books of Lucian's True Story? writ-

ten in Greek, which I chose as my means of mastering the language. I was helped by my enjoyment of the highly daring tale,

Latin is scheduled to be included in Gesam. Werke, XII, when that volume is ready; meanwhile it can be consulted in the 1634 Sommium, pp. 97-184, and Frisch, VIII, 76-123. 6. Christopher Besold (1577-1638) entered Tübingen University when he was

fourteen years old. Twelve months later he was awarded a bachelor's degree, and

in 1593, when his older fellow-student, Kepler, gave him some ideas about the moon to be used in an academic disputation, he was a candidate for the M.A. Having obtained this degree on September 5, 1593, he went on to study law. Six

years later he received his doctorate in that subject. He joined the faculty of Tübingen University as professor of law in 1610, and taught there for the ensuing quarter of a century. "You were once my faithful teacher," Besold reminded Kepler in a letter written in 1605 (Gesam. Werke, XV, 130:4). Although Besold and

Kepler sometimes disagreed on basic issues, they nevertheless remained the best of

friends. For example, when Kepler's only sister, Margaret, was being wooed, Kepler asked Besold for information about the suitor (Gesazz. Werke, XV, 316-17). When Besold published his thoughts about the New World, Kepler was one of the three persons to whom he dedicated the book (Gesam. Werke, XVII, 283:1415; 313:9; 495). For Besold’s record as a student, see Matrikeln . . . Tübingen, I, 682, and for his part in the trial of Kepler's mother as a witch, sce Edward Rosen, "Kepler and Witchcraft Trials," The Historian (1966), 28:447-50. 7. One of Kepler's essays maintained that the first motion, or apparent daily ro-

tation of the heavens, is merely an appearance caused bv the actual rotation of the earth (Gesam. Werke, I, 9:16—17; see fn. 177, below). 8. Since Besold's theses concerned the moon, they were based not on the essay

mentioned in fn. 7 which I wrote . . XIII, 39:243-44; cf. 9. See Appendix

10. The

but, as Kepler put it, on "the disputation concerning the moon . but which Besold was prepared to defend" (Gesam. Werke IV, 199:5-9). C, "Kepler's Lunar Dissertation of 1593."

True Story was included

Turner of Lucian's Satirical Sketches

in the recent English translations by Paul

(Baltimore:

Penguin

Books, Ltd.,

1961).

)

Kepler’s Notes on the Dream

33

which nevertheless offered some intimations concerning the nature of the entire universe, as Lucian himself announces in his introduction.’? He, too, sails out past the Pillars of Hercules into the ocean

and, carried aloft with his ship by whirlwinds, is transported to the

moon.'^ These were my first traces of a trip to the moon, which

was my aspiration in later times.’* At Graz, in the year 1595, I first encountered Plutarch's book, to which my attention was directed

by reading Erasmus Reinhold's commentary on Peurbach’s Theories.^ At Prague, in the year 1604, I quoted extensively from r1. Here

Kepler attaches great weight to a very slender thread in Lucian's

de-

sign. While the satirist did faintly profess to be "exhibiting a not uninformed view," he admitted that “nothing I say is true. Moreover, I am writing about things which I have neither seen nor felt nor heard from others. Besides, they do

not exist at all, nor can they even have come into being. Hence my readers must not in the least believe them" (True Story, Secs. 2, 4). 12. Lucian “once started out from the Pillars of Hercules and headed into the western ocean" (True Story, Sec. 5); "suddenly a whirlwind arose, spun the ship around, and lifted it up" (Sec. 9); the ruler of the land to which he was carried "said that that land was the moon, which shines down on us" (Sec. 11). 13. Hence, in the lunar dissertation which Kepler wrote in 1593, astronomical observers were already on the moon. At that time Kepler had not yet conceived the idea of transporting an observer from the earth to the moon. That idea was

the principal feature of the Dream framework, which Kepler built in 1609 around

his student dissertation of 1593. 14. George Peurbach (1423-61) wrote an introduction to astronomy under the title New Theories of tbe Planets, which was first published about a dozen years

after his death. This highly popular textbook was later reissued with explanatory commentary by Erasmus Reinhold (1511-53), who inserted an essay of his own on “The

Light

of the Moon"

("De

illuminatione

lunae").

Here

Reinhold

said:

“With regard to the matter composing the moon's body, there are many different

opinions of various philosophers, which students will look up in Plutarch, Diogenes Laertius, and others." It was this remark of Reinhold's that directed Kep-

ler's attention to Plutarch's Moon.

Kepler called “Reinhold’s commentary on Peurbach's Theories very learned and worthy of being read carefully by students of astronomy" (Gesam. Werke, II, 204:15-17). It was Kepler's judgment that “in this one little book there is more illumination than in all” the writings of a celebrated contemporary, Joseph Justus

Scaliger

(Frisch, VIII,

275:27-28).

In the first edition

of Reinhold's

Peurbach

(Wittenberg, 1542), as in many other early printed books, the pages are not numbered. Instead, the gatherings or signatures are indicated by letters of the alphabet,

while the leaves or folios within each signature are numbered as a separate group. In the

1542

edition, the reference

to Plutarch

occurs

on the verso

of folio

5 of

signature T (Tsv). In the second edition (Wittenberg, 1553) the reference to Plu-

tarch occurs at fol. 163v. Since fol. 164, not fol. T6r, is cited by Kepler (Gesam. Werke, II, 203:26, 237:40), he used the second edition (as was pointed out by Hammer in ibid., 450). It is likely that Kepler studied Reinhold carefully in con-

nection with his new duties in 1594 as the teacher of mathematics and astronomy

34

Kepler’s Notes on the Dream

Plutarch in my Optical Part of Astronomy. Nevertheless, the 1slands mentioned by Plutarch in the ocean around Iceland were not

responsible for my choice of Iceland as the starting point of my

dream. Among

the reasons, however, there was the following. At

that time there was for sale in Prague Lucian's book about the trip to the moon, as translated into the German language by Rollenhagen’s son; !* bound with it were the stories of St. Brendan '' and

St. Patrick's Purgatory ?? in the earth beneath Mt. Hekla, the Ice-

landic volcano.!® Moreover, since Plutarch, in accordance with the belief of pagan theology, located the purgatory of souls on the moon,? I decided that when I set out for the moon I would most at Graz. In a letter of 1599 Kepler cited a proof used by Reinhold in his "Light of

the Moon," the essay in which Kepler first saw Plutarch mentioned as a source of information about the moon (Gesam. Werke, XIII, 340:36-37; 419).

15. Kepler wrote the epoch-making work in which he laid the foundations of

modern

optics while

he was

living in Prague.

But

the treatise was

published

at

Frankfurt/Main in 1604. It bore a typically long title in fourteen lines, the first six of which mean: “Additions to Witelo, in which the Optical Part of Astronomy 1s Expounded.” When citing it, Kepler sometimes called it, as he does here in Note 2, the Optical Part of Astronomy, but usually he referred to it more

Optics. He included in it fourteen quotations from Plutarch’s Moon

briefly as his

(see Appen-

dix D). 16. George Rollenhagen (1542-1609), in his time a very widely read German poet, was the rector of a school at Magdeburg. In that city, in 1603, his son, Gabriel, published Vier Bücber wunderbarlicher . . . Reysen (Four Books about Wonderful Journeys), Lucian’s True Story being the third item. For the literature concerning George Rollenhagen, see Eli Sobel, Publications of the Modern Language Association (1955), 70:762-80. For a study of Gabriel Rollenhagen's life and work, see Karl Theodor Gaedertz, Gabriel Rollenbagen (Leipzig, 1881). 17. St. Brendan the Navigator has been aptly called the Odysseus of Ireland.

Many old pagan stories were attached to his name and given an edifying Christian

flavor. They were incorporated into his Life, which was translated into English by William Caxton as one of the hagiographical biographies in his Golden Legend (Westminster, 1483), fols. 394v-398v. A somewhat more embellished version of the legends became very popular in the Middle Ages under the title The Voyage of

St. Brendan. The original Latin text of this Voyage has been lost. It was probably composed in the tenth century somewhere near the Rhine, according to Carl Selmer,

Navigatio

S. Brendmi

(South

Bend,

Indiana:

University

of Notre

Dame,

1959), pp. xxviii-xxix.

18. In the legend of St. Patrick's Purgatory, as first written down in the twelfth century, the place where the pious might have a preview of the afterlife was lo-

cated somewhere in Ireland. Later this place was identified as Lough Derg, which

the historic St. Patrick never visited; see Ludwig St. Patrick (Dublin, 1949), p. 26. 19.

For

the

reason

indicated

Purgatory in Iceland, not Ireland. 20. Plutarch, Moon, 943C; Frisch, VIII, 101:14-17.

in

fn.

Kepler’s

76,

below,

translation

Bieler, The Life and Legend

of

Kepler

to

in the

located

1634

the

entrance

Somnium,

p.

175:

Kepler's Notes on the Dream

35

prefer to take off from Iceland. A greater recommendation of this island

came

from

a report

of Tycho

Brahe,

concerning

which

something will be said below.?! Of some effect also was my recollection of reading the account of the Dutchmen who spent a win-

ter on icy Novaya Zemlya;?? this account also supplies a large number of astronomical exercises incorporated by me in my Opti-

cal Part of Astronomy in 1604.”

3. On a wall in the house which I used by permission of Martin Dachaczek,?* rector of Charles University,” there used to hang a very old map of Europe, on which the word “Fiolx” was attached to localities in Iceland. Whatever it signified,?? its harsh sound de21. See Kepler's Note 15. The standard biography of the great Danish omer remains Tycho Brahe, by John Louis Emil Dreyer.

astron-

22. In the closing years of the sixteenth century three unsuccessful voyages in

search of a northeast passage to China were made by Dutchmen. One of them, Gerrit de Veer, published an account of these voyages in Dutch at Amsterdam in 1598. Two months later the same publisher issued a Latin translation entitled Diarium nauticum, a copy of which was sent to Kepler by his friend Colmann Zehentmair on May 24, 1599 (Gesam. Werke, XIII, 338:24). The English translation of 1609 was reprinted by the Hakluyt Society in 1853 and again in 1876. In this second Hakluyt edition, The Three Voyages of William Barents to the Arctic Regions, the story of the winter spent on Novaya Zemlya occurs at pp. 99-194; reprinted, New York: Franklin, 1963.

23. Gesam. Werke, Il, 128-32. 24. Bachaczek wrote to a friend

on March

2, 1605:

“His Imperial

mathematician, Johannes Kepler, is living with me. We often meet serve the nova . . . . For this purpose I am having a little wooden and the work is already under way. Observations with mathematical will be made from it” (Gesam. Werke, XV, 169, No. 334:1-6). Later, lar Pbenomenon (Leipzig, 1609), Kepler cited Bachaczek as a witness vation he made on May 18/28, 1607 (Gesam. Werke, IV, 93:7-12).

To

Majesty's

and also obtower built, instruments in his Singuof an obser-

25. Ihe Holy Roman Emperor Charles IV founded Prague University in 1348. celebrate the six-hundredth anniversary of the founding, Otakar Odlozilik

published a brief history of The Caroline University 1348-1948 (Prague, 1948). 26. By saying “whatever it signified,” Kepler implied that he did not understand

the meaning of “Fiolx.” Here the parallel between Kepler and his fictional counterpart Duracotus breaks down. Having been born and brought up in Iceland, Duracotus knew the Icelandic language. But Kepler did not. There is no such word

as “Fiolx” in Icelandic. On

some

early maps

Iceland

was

called “Fixlanda,”

"Fixlandia," or "Frixlanda"; see Halldór Hermannsson, “The Cartography of Ice-

land," Islandica (1931), 21:12-13, Plates 3, 5, and 7. But these transient names cannot have been what Kepler misread, since he savs that “the word ‘Fiolx’ was attached to localities in Iceland," not to the whole island. Maps often attached to

many localities in Iceland the word "fjórór," meaning “fiord.” Did Kepler misread

the Icelandic letter "6," (edh, pronounced “th”), as “x”? Or was the wall map printed in a font whose lower-case “r” looked like an "x"? Kepler's evesight was none too good (Rosen, Kepler's Conversation, n. 88), and even people with nor-

mal vision find the legends on most early maps hard to decipher.

36

Kepler's Notes on the Dream

lighted me, and I appended

“Hilde,”?* a familiar designation of

women in the ancient tongue, whence the names Brunhilde, thilda, Hildegard, Hiltrud, and the like are derived.

4. Because

this is more

plausible with

regard

Ma-

to a son who

divulges his mother's arts, than if he were conceived to be writing while she was alive.22 However, I wanted to make this further

suggestion: untutored experience or, to use medical terminology,

empirical practice is the mother who gives birth to Science as her

offspring. For him it is not safe, so long as his mother, Ignorance,

survives among men, to reveal to the public the deeply hidden causes of things. He must rather forbear to injure the venerable beldam, while waiting for the fullness of years which will finally

bring about the death of Ignorance, decrepit with old age. The purpose of my Dream is to use the example of the moon to build

up an argument in favor of the motion of the earth,?? or rather to overcome objections taken from the universal opposition of mankind. This ancient Ignorance was then, I thought, already dead enough and erased from the memory of intelligent men. Yet the creature still struggles on in a tangle of so many knots tied tightly together through so many centuries. The aged mother continues to exist 1n the universities, but such is her existence that seemingly

she ought to look upon death as more desirable than life. [5. Missing. |

6. On my recent journey ?? the following incident happened to

me, and yet not to me alone, but to a group of many like-minded persons. A theologian who professed the Augsburg Confession ?! 27. "Hilde" meant “female warrior"; see Erwin Metzner, Die deutschen Vornamen, 2d ed. (Goslar, 1939), p. 86. 28. Kepler undoubtedly intended the parallelism between his fictional Fiolxhilde and his own mother Katharine to hold good in this respect. If he felt free to write

about these matters only after his mother's recent death, then he started to com-

pose the Notes on the Dream in 1622, after April 13 (Introduction, p. xix, above). Kepler mentioned the date of his mother's death in a letter to his friend Peter Crüger (Gesam. Werke, XVIII, No. 993:572). 29. Kepler's astronomical purpose in writing the Dream was to adduce a novel

argument in favor of Copernicanism by transferring the observer from the earth

to the moon. 30. From Linz, journeyed in the defend his mother year, he returned 31. The official

the capital of Upper Austria, where Kepler was then living, he autumn of 1620 to Württemberg for the purpose of helping to against charges of witchcraft. After an absence of more than a to Linz in November, 1621 (Frisch, VIII, 873:2-3; 878:22). creed of the Lutheran church. Naturallv, for reasons of pru-

Kepler’s Notes on the Dream

37

attacked us with great vehemence. He was convinced that he was drawing from Scripture weapons with which to assail us. Finally, becoming enraged by our self-defence, he raised his voice and, call-

ing on everything sacred as witness, he shouted that this teaching

was “in conflict with all reason.” Then I finally broke my stubborn silence (for up to that time I had been sitting there merely listen-

ing) and said: “No doubt it is this which impels even the ignorant

men in your faction. For if the usefulness, necessity, and possibility of this teaching were understood by your narrow mind, you your-

self would long ago have discounted the force of the arguments drawn

from

Scripture,*? and sought out a suitable interpretation,

dence, Kepler is careful not to mention the name of this anti-Copernican Lutheran

theologian. But Kepler dated the encounter "in the year 1620" by means of a sidenote (Somnium, 1634 ed., p. 31).

32. Kepler was both a sincere Christian and a convinced Copernican, as he dem-

onstrated in his first major work, the Cosmographic Mystery, published at Tubingen in 1596. As Chapter 5, he wrote a reconciliation between the Bible and Copernicanism (Gesam. Werke, XIII, 203:33-34). This whole chapter was then omitted

by Kepler on the advice of the Tübingen faculty. However, Kepler's brief reference to this subject in his first chapter was retained (?bid., I, 14:21-29). In 1598 Kepler wrote to Michael Mastlin (see fn. 131, below), the Tübingen

professor who had introduced him to Copernicanism: "Let us imitate the Pythagoreans even in their customs. If anybody approaches us privately, let us tell him our opinion frankly. Publicly let us be silent. Why go and ruin astronomy by means of astronomy? The whole world is full of men of the type who are ready to throw all of astronomy, if it sides completely with Copernicus, off the earth,

and to forbid the specialists an income. But specialists cannot live off themselves or

on air. Therefore, let us act in astronomical affairs in such a way that we hold on to the supporters of astronomy and do not starve”

(Gesam.

Werke, XIII, 231:505-

12). However, after Kepler was appointed Imperial Mathematician, in the Intro-

duction to his greatest work, the New Astronomy (Heidelberg, 1609), he courageously contended that Copernicanism is compatible with the Bible (Gesam. Werke, Ill, 28:26-34:5). This section of his Introduction was often reprinted (Caspar, Bibliographia Kepleriana, p. 111). It was translated into English by Thomas Salusbury, Mathematical Collections and Translations, Tome I (London, 1661), Pt. I, pp. 461-67. Rheticus’ First Report (the letter which had first publicized Copernicus’ theory) was appended to Kepler's Cosmograpbic Mystery "even though Kepler was unaware of the fact, and was not consulted because he was not there" (Gesamı.

Werke, I, 85:23, and XIII, 95:29-30). This action was taken by Mastlin, whom

Kepler had entrusted with the supervision of the printing of the Cosmographic Mystery. One of Mastlin’s three reasons for appending Rheticus’ First Report was

that “it is, as it were, a brief commentary on many of Copernicus’ more obscure passages”

(Gesam.

Werke,

XIII, 97:95-96). In addition, Mastlin

told

Kepler

that

he appended Rheticus’ First Report also “because you mention it frequently, and

because

it

clarifies

many

passages

in

your

Cosmographic

Mystery”

(Gesam.

38

Kepler’s Notes on the Dream

as you are not infrequently in the habit of doing on other occasions. But now your mind is so feeble that you fail to see that on our side, too, there is some particle of reason. Therefore a teaching is not in conflict with all reason which is not in conflict with the reasoning of astronomers and physicists. For what someone fails to understand may be understood by someone else more familiar with the subject.”

7. Everybody suffers his own injustice. The chief injustice to Copernicus’ work on the Revolutions ** comes from people who know nothing about astronomy (interpreting the censure of the book ** not in accordance with the author's thinking, but incor-

rectly). They believe that this work must not be read unless the motion of the earth is first eliminated.?? This amounts to the same

thing as saying that it must not be read before it has been burned up in flames. Judging that these people should be refuted not with arguments but with a laugh, I composed the following epigram: They were able to castrate The bard lest he fornicate; He survived without any testicles.

Alas, O Pythagoras,

Whose

thinking wore out iron chains;

They spare you your life, But first they get rid of your brains.

8. I suppose that a copy of this little work fell into the hands of

the author of the bold satire entitled Ignatius His Conclave? for Werke, XIII, 97:94-95, and I, 85: 18-19, 24-26). In Mästlin’s judgment, then, both Co-

pernicus and Kepler were made clearer by Rheticus’ First Report, of which an English translation may be found in Edward Rosen’s Three Copernican Treatises, 2d ed.

(New York:

Dover,

1959), pp.

107-96. The Latin text of the First Report

(Narratio prima, Danzig, 1540) has been reissued (Osnabriick: Zeller, 1965), with

an epilogue by Bern Dibner.

33. Nicholas

Copernicus,

De

revolutionibus

orbium

coelestium

1543); English translation, On the Revolutions of the Heavenly Books, Vol. 16, pp. 501-838.

34. In

1616 the

Roman

"until corrected”;

Catholic

church

suspended

Copernicus’

Latin text of the decree, Galileo, Opere,

translation, Giorgio de Santillana, The Crime of Galileo Press, 1955), p. 123.

(Nuremberg,

Spheres, in Great

XIX,

Revolutions

322-23;

English

(University of Chicago

35. Kepler refers to the “corrections” made in Copernicus’ Revolutions by the

Roman Catholic XIX, 400-401.

church

ymously.

Kepler

in

1620;

Latin

text

of the

corrections,

Galileo,

Opere,

36. See Appendix E. Ignatius His Conclave (London, 1611) was published anonHence

was

unaware

that

its author

was

John

Donne

(1573-

Kepler’s Notes on the Dream

39

he stings me by name at the very outset.? Later on he brings poor

Copernicus to Pluto’s court,®® which is entered, unless I am mistaken, through the chasms of Hekla (2, 5, 9).°® You, my friends, who are familiar with my affairs and with the reason for my last

trip to Swabia,*? especially those of you who have met with the

manuscript before, will be of the opinion that this little book and those events were ominous for me and my family. Nor do I disagree. Dire, indeed, is the omen of death when a fatal wound is inflicted, when a poison is swallowed; apparently no less dire was the omen of domestic disaster when this writing was circulated. You

might suppose that a spark dropped on dry tinder; by this I mean

that those words fell upon minds which were dark within and sus-

pected everything of being dark. The first copy *! was taken from

1631), who preacher.

afterwards

37. "Keppler, who

achieved

recognition

as an outstanding

poet,

satirist, and

(as himselfe testifies of himselfe) ever since Tycho Braches

death, hath received it into his care, that no new thing should be done.in heaven without his knowledge" (Ignatius His Conclave, Facsimile Text Society, No. 53 [New York: Columbia University Press, 1941], p. 3). 38. In Donne's satire Copernicus demands admission to the chamber in Hell re-

served for those who "had so attempted any innovation in this life, that they gave an affront to all antiquitie, and induced doubts, and anxieties.” Opposing Copernicus’ demand,

the founder

to this place,

that those

of the Jesuit order tells him:

'* . . . this detracts from

the dignity of your learning, and derogates from your right and title of comming opinions

of yours

may

very

well

be

true."

The

Jesuit

prefers another astronomer "who opposed himselfe opportunely against you, and the truth, which at that time was creeping into every mans minde." Later the Jesuit says: “ . . . if heereafter the fathers of our Order can draw a Cathedrall De-

cree from the Pope, by which it may be defined as a matter of faith: That the earth doth not move; and an Anathema inflicted upon all which hold the con-

trary: then perchance both the Pope which shall decree that, and Copernicus his

followers, (if they be Papists) may have the dignity of this place" (Ignatius His Conclave, facsimile ed., pp. 6, 18-19, 21-22). These prophetic words were published by Donne in 1611, five years before Copernicus’ Revolutions was suspended "until corrected" (see above, fn. 34). 39. For the source of this notion about Hekla, see fn. 76, below. In the Somnium (1634 ed., p. 32), the parenthesis refers to Notes “3, $, 8, 9." These numbers all by themselves suffice to show that the Sozmium, when first published, was not flawless. Thus Frisch (VIII, 41:6 up) had to replace “3” by “2.” He left "5" although it is missing, and he deleted "8," a pointless reference to itself. In short, of the four numbers in the parenthesis as printed in the 1634 Somnium, only "9" is correct. 40. See fn. 3o, above. 41. Primum quidem exemplar: “the first copy." Kepler's exemplar does not mean “draft.” Kepler would hardly have permitted the "first draft" of the Dream

to be taken away, although to his sorrow he did allow the "first copy" to be taken

away. The first draft, which he had written long before, in 1593, did not contain the “ominous” words added in 1609.

40

Kepler's Notes on the Dream

Prague to Leipzig and from there to Tubingen in the year 1611 by Baron von Volkersdorf *? and his tutors in deportment and studies. Would you believe that in the barber shops (especially if there were any people to whom the name of my Fiolxhilde is ominous on account of her occupation) ** there was chatter about this story of mine? Indeed, from that very city and house there emanated malicious gossip about me in the immediately ensuing years. When this gossip was taken up by senseless minds, it flared up into defamation, fanned by ignorance and superstition. If I am not mistaken,

you will judge that my family could have gotten along without

that trouble for six years,** and I without last year’s journey,” had I not violated the precepts of this Fiolxhilde in the dream.*® I therefore decided to avenge this dream of mine for the affair just 42. The

baron's

name,

being

the only

word

in the

1634

Somnium

which

was

printed in a heavy black-letter font, thereby received great emphasis. This prominence was given to Volkersdorf by Kepler himself, since the Notes on the Dream were printed while he was still alive, and he personally read the proofs (Introduc-

tion, pp. xx-xxi, above).

But who was this Baron von Volkersdorf? Although an absolutely certain identification may no longer be possible, I suggest that the baron mentioned by Kepler may have been Wilhelm von Volkersdorf. As the third of that name, he was born on July 3o, 1595. "Having completed

his studies, he undertook a

trip to Italy and

planned, after visiting several princely courts, to go from Florence to Naples"

(Ferdinand Wirmsberger, Beiträge zur Genealogie der Dynasten von Volkensdorf, Wels, 1863, p. 121). Although the family name appears in this genealogy as “Volkensdorf,” in the last will and testament of the father of Wilhelm III, as in

many other similar documents, the surname was spelled "Volckerstorff" (Wirmsberger, Genealogie, p. 199). There are additional reasons for identifying Kepler's baron with Wilhelm, who in 1611 was sixteen years old. At that age a traveling young nobleman was usually accompanied by “tutors in deportment and studies." Before going on to Italy, Wilhelm may well have wished to see Prague, the imperial capital, and the university towns, Leipzig and Tubingen. At the age of sixteen,

furthermore, Wilhelm may have indulged in a little mischief at the expense of the Imperial Mathematician. The latter, in turn, would then have felt no compunction

in emphasizing Baron von Volkersdorf’s name in his Note 8, which Kepler wrote about a decade after Wilhelm fell sick in Florence and died there in his eighteenth

year on October 18, 1612 (Siebmacber's Wappenbuch, Band 4, Heft 5, p. 544). 43. Fiolxhilde's name was ominous to superstitious people who heard that her oc-

cupation was selling dried herbs. 44. Kepler first learned about his mother's legal entanglement when he received a letter from

his sister Margaret

in

1615

(Gesam.

Werke,

XVII,

154:4-7).

The

prolonged court battles ended when his mother was finally acquitted and released from custody in 1621 (ibid., XVIII, 212:568-70). Thus his family's troubles lasted six years, from

1615 to 1621.

45. Ihe journey took Kepler away from Linz throughout most of 1621, and he

returned in November of that year (see above, fn. 30). Since he here refers to “last year’s journey,” he wrote Note 8 in 1622 (Introduction, pp. xix-xx, above). 46. Fiolxhilde's precepts may be paraphrased as follows: Don't write, because

Kepler's Notes on tbe Dream

41

cited by publishing the book,** which will be another punishment for my adversaries.‘

9. Ihe history of volcanic Mt. Hekla *? is known

and books on geography.

from maps

As for the type of punishment,

I was

thinking about Empedocles in the fable, as I regard it. According

to Diogenes Laertius, Empedocles climbed Mt. Etna in order to obtain divine honors after his death. He hurled himself into the crater

and sacrificed himself alive ?? in the flames, as the story goes."

stupid people will make trouble for you. As Günther put it: "It is clear from Kep-

ler's account that he later thought he must reproach himself for these remarks, and

suspected that his tragic fate and the prosecution of his aged mother as a witch were caused in part by the unrestrained expressions which his fanatical opponents misunderstood or deliberately distorted" (Traum, p. 27).

The great services to Kepler scholarship of Ludwig Günther (1846-1910) should not be undervalued. He longed to understand Kepler's genius, and to throw light on the eminent scientist’s biography and achievements. What he published may not be accepted in every case as the last word on the subject. But it was often the first word, and it is always worth pondering. The major portion of his translation

of the text of the Dream

(1958), 14:433-41.

was

reprinted

in Phystkalische

Blatter

47. Having published neither the lunar dissertation of 1593 (see Appendix C) nor the expanded version of 1609 (Introduction, p. xix, above), Kepler decided to

publish the Dream

after his mother's

trial ended.

Günther

correctly

and

elo-

quently declared: "In such troubled times, with ignorance and superstition in the saddle, and witch trials on the order of the day, to publish such a work bore witness to Kepler's extraordinary sincerity and courage. However, in order to oppose the forces of evil to the best of his ability, and to refute all the hostile allegations which the circulation of the text against his wishes and the malicious interpreta-

tion of it had raised up against him, he now deemed it essential to make the book, together with detailed explanations, available to a larger circle. Unfortunately, his premonitions of death were destined not to deceive him; he died, as we know, before the work appeared" (Traum, p. 28). 48. What did Kepler declare to be the reason

for his decision

to publish

the

Dream? He wrote it in violation of the maternal precept never to write anything. Having been written, it was used by his enemies to accuse his mother. But she was acquitted, and they were punished, first by being condemned to pay three-fourths

of the costs of the trial (Caspar, Kepler, tr. and ed. Hellman, p. 256; Frisch, VIII,

550:6 up-551:5). "Another punishment for my adversaries,” Kepler hoped, would be the publication of the Dream,

disclosing to the world

at large the little book's

partly jocular, partly scientific character, in which there never was anything sinis-

ter or malevolent. 49. There were fierce eruptions of Hekla in 1597 and 1619; see G. Einarsson G. Kjartansson, Heklugos: Tbe Eruption of Hekla, 1947 (Reykjavik, 1947), 128-29. George H. Boehmer's Bibliography of the Volcanoes, Earthquakes, Geysers of Iceland is still useful (Srmithsonian Institution, Annual Report, 1885,

513-41).

50. The misprint vivuts in the (VIII, 42, Kepler's Note 9:4).

1634 Sommium

and pp. and pp.

was corrected to vivus by Frisch

sı. Diogenes Laertius, Lives, viii.ó9, quoting from a lost work on the history of

42

Kepler s Notes on the Dream

Perhaps in searching for the causes of the everlasting fire he went

so far forward with blind audacity that he could not get back. As the encrusted surface of the ashes opened beneath his feet, he re-

pented his curiosity too late. Not through hankering after this fame, but with lamentation and against his will did he lose his

life? For a similar fate befell Gaius Pliny. When Vesuvius erupted disastrously, Pliny proceeded through dangerous showers of ashes and rocks to Pompeii, for the purpose of investigating nature, and was suffocated by stinking sulphur and cinders choking

his breathing.®* In legendary tales Homer is similarly said to have

thrown his life away in the water when he was tormented by the riddle of the fishermen,®* and Aristotle by the ebb and flow of Euripus.?? In like manner most people

expiate their love of science

philosophy. For a scholarly analysis distinguishing fact from Bidez, “La Biographie d'Empédocle," Université de Gand, Philosophie et Lettres (1894), 12:6-9, 35-40, 89-91, 174-76.

fable, see Joseph

Recueil

de

Travaux,

52. The idea that Empedocles fell into Etna against his own will was suggested by Diogenes Laertius himself (Lives, viii75). The legendary scene tempted the

conservative British poet Matthew Arnold, who excluded his Empedocles on Etna (1852) from his collected Poems (1853) because he felt that no enjoyment could be derived from the tragic situation he had depicted. Empedocles! death attracted also the deranged German writer Friedrich Holderlin (1770-1843); his various treatments of the theme were sympathetically studied by the late Walther Kranz, Empedokles: Antike Gestalt und romantische Neuschöpfung (Zürich, 1949). 53. Ihe death of Pliny the Elder, author of the Natural History, was described

by his nephew, Pliny the Younger (Letters, vi.16), at the request of the historian Tacitus.

54. "While sitting on a rock, Homer

saw fishermen

sailing toward

asked them whether they had anything. Having caught nothing and catch, they were picking lice off themselves, and answered as follows:

him. He

lacking

a

What we caught we left behind;

What we didn't catch we are carrying along.

They intimated, namely, that they had left behind those of the lice which they caught and killed. But those which they had not caught they were carrying in their clothes. Because he could not understand this, Homer died of despondency."

This version of the louse riddle was embedded

etry of Homer,"

in an essay “On

the Life and Po-

which was formerly attributed to Plutarch. It was frequently

printed in early editions of Homer and of Plutarch. For the Greek text, see Bernardakis' edition of Plutarch's Moralia, VII (Leipzig, 1896), 332:2-12, or the Oxford edition of Homer, V, 242:63-71. The idea that Homer committed suicide by

drowning himself may have been Kepler's contribution to the legend.

$5. Euripus, the narrow strait between the island of Euboea and the mainland of central Greece, exhibits strong tidal currents. For “Kepler’s Legendary Account of Aristotle's Death," see Appendix F.

Kepler’s Notes on the Dream

43

by being poor and incurring the hatred of the ignorant rich."

10. [joked about the barbarous customs of the uneducated. Furthermore, if you grant, as I did above,’ that the mother of science

is Ignorance, and that the father in reality is Reason, of course this father is quite properly either not known by that mother or concealed by her. rr. Buchanan, the author of a historical account of Scotland and

the Orkneys, mentions a fisherman who at the age of 150 became

the father of several children by a young wife.’® 12. Because higher up there are snows and crags, and at the summit,? flames from the depths of the earth, as the histories testify.

13. Because Iceland is situated near the Arctic Circle. So I

heard also from Tycho

Brahe, who

based these calculations on a

report by an Icelandic bishop.?! 14. Medicine and astronomy are related studies, arising from the same source, the desire to understand natural phenomena.” empirical botany is generally associated with superstitions.

But

56. This bitter cry of anguish has an unmistakably autobiographical ring to it. 57. See Kepler's Note 4. £8. In the last sentence of Book I of his History of Scotland, George Buchanan

spoke of a man “who married a wife after he was 100 years old. When he was 140, he used to go fishing in his own little boat in the roughest sea” (ed. 1582, fol. 13, ll. 85-88). In Kepler's imprecise recollection of this passage, the fisherman became a

father of several children, about whom Buchanan is silent. Moreover, the Scot does not say that the wife was young, a romantic embellishment added by Kepler, who raised the fisherman's age from 140 to 150. Buchanan's History of Scotland

deals with the Orkneys only in the closing part of the first of his twenty Books. 59. Here Kepler uses "higher up" and “at the summit" in deliberate contrast with the text's “lower slopes," which were not dangerous.

60. The Arctic Circle grazes the northernmost point of Iceland. Fiolxhilde's favorite time for her excursions could have been identified by Kepler in a purely astronomical way as the summer solstice. Instead, he chose to mention St. John’s Day

(June 24), thereby evoking the old pagan folklore still surviving in the nomi-

nally Christian celebrations of that saint’s day. This device was doubtless intended to intensify the eerie effect for which Kepler was striving. 61. This bishop was Oddur Einarsson (1««0-1630), for whom see Appendix G. “The see of the northern diocese of Iceland" was located by Brahe at 65° 44' North Latitude. This see, which in those days was Holar, was the northernmost of the places whose longitude and latitude were determined by Brahe in a table printed by his pupil Christianus Severini Longomontanus (Christen Sórenson Longberg), Astronomia Danica, 2d ed. (Amsterdam, 1640), p. 199, right-hand column: 12 up; Brahe, Opera omnia, V, 312:19, left-hand column. 62. In 1600 Kepler ceased to be a schoolteacher, when he refused

to become

a

44

Kepler’s Notes on the Dream 15. The geographers commonly say, whether rightly or wrong-

ly, that the pilots of ships sailing from Iceland produce whatever wind they want by opening a wind bag. If this saying is transferred to the rhumbs of the nautical rose, magnetic needle, and rudder control, it is very nearly true. The winds are thirty-two in number. Whichever one of the sixteen in one hemisphere is blowing, if the

skill of the helmsman is added, steering by the rose and managing

the rudder will speed the ship along the chosen course in that hemisphere. On the other hand, so long as winds from the opposite hemisphere are parried by traveling sidewise back and forth in the maneuver called “tacking,” those winds are transformed into one of those from the opposite hemisphere. 16. The Icelandic bishop informed Tycho Brahe that the Icelandic girls, while listening to God’s word in church, are accustomed to copy some of the expressions or words that they hear by sewing them on linen with needle and colored thread with amazing speed.

d 17. Passing by Scotland and the Orkneys in the northern ocean.

18. Of course he lacked the bag, so that he was unable to escape the buffeting of the north wind and reach his destination, Norway.

19. So Tycho told me, as in Note 13, above.

20. Tycho Brahe writes to the Landgrave of Hesse *? that reindeer, a species of northern stag, do not last long in Denmark because that country, however cold it is, 1s nevertheless much warmer than Bothnia, Finland, and Lapland, where this animal is

native.°* Ihe same degree of cold may therefore be properly attributed to Iceland, which also 1s located near the North Pole.

Catholic (Frisch, VIII, 734:9 up-735:3-5). His hope of continuing his astronomi-

cal work

as an associate

of Tycho

Brahe

was

still balanced

on the

edge

of the

razor. In that painful period of uncertainty about his future, his thoughts turned toward medicine. Hence he wrote to Mastlin: “I shall enter upon a medical career. Perhaps

you

will give me

an assistantship”

(Gesam.

Werke,

XIV,

151:46).

But that door refused to open. On the other hand, Kepler did become a member

of Tycho’s staff, and his successor as Imperial Mathematician. What medicine lost, astronomy gained. 63. William IV (1532-92), himself an ardent astronomer, recommended Brahe

most highly to the king of Denmark. The royal grant of the island of Hven to

Brahe followed shortly thereafter. Brahe and William IV remained and maintained an active correspondence. 64. Tychonis Brahe ... opera, VI, 230:18-23, 235:8-14; English Dreyer, Tycho Brabe, p. 210.

close friends summary

in

Kepler’s Notes on the Dream

45

21. That island ® has no inhabitants other than fishermen because it is barren, rocky, and small.®

about

forty

22. It was the habit of that true philosopher never to stop asking questions, acquiring information, valuing such reports highly,

thinking about them repeatedly, and applying them to the laws of nature.

23. Although they are equally Teutonic, there is a very great

difference between the dialects of Denmark and of Iceland.9* The latter 1s apparently a colony of the Norwegians, who had control of it and of nearby Greenland a century ago.°® The Orkneys, too, of

65. Brahe established his observatory, which he called Uraniborg, on the island Hven (Tychonis Brahe... opera, V, 139:20-23, 28-33). Brahe determined

the longitude of Uraniborg as 36° 45’ east of the traditional prime meridian (ibid.,

312:46, col. 2). Nowadays Hven’s longitude is given as 12° 42' east of Greenwich. 66. Kepler's description of Hven conforms to his literary requirements rather than to the actual historical situation. For the purposes of his Dream it was un-

doubtedly desirable to depict the island as barren and inhabited only by fishermen, about forty in number. Such a grim picture would

add another touch

of somber

color to the supernatural background Kepler was conjuring up. But when Brahe published his map of Hven, in the center of the island he marked a “village con-

taining about forty farmers’ dwellings," which are individually numbered on the map (Tychonis Brahe . . . opera, V, 150, 151:4-5; English translation in Tycho Brabe's Description of His Instruments and Scientific Work, trs. and eds. Hans Raeder, Elis Strómgren, and Bengt Strómgren, Copenhagen, 1946, p. 139). In 1671, when Jean Picard, accompanied by Erasmus Bartholin and Olaus Rómer, visited Hven, he found “some farmhouses” (Picard, Voyage d'Uranibourg, Paris, 1680, p. 5, in Recueil d'observations faites en plusieurs voyages, Paris, 1693).

67. Most of the early settlers in Iceland were Norwegians, who brought their

speech with them. Icelandic became a

distinct language in the fourteenth

century

by preserving the old inflections when these were sloughed off by Norse, which

underwent other important changes at the same time. On the other hand, Icelandic and Danish belong to separate branches of Old Scandinavian, and differ so much as to be mutually unintelligible. Thus, when the king of Denmark in 1602 granted to a Danish company a monopoly on trade with Iceland, he put "the inhabitants at the mercy of Danish tradesmen who with their agents and clerks understood little of the Icelandic tongue"; later, "there were cases where the laws had been proclaimed to the people only in Danish, a language they did not understand, with the consequence that . . . the Danish Supreme Court declined to enforce laws which had not been promulgated in Icelandic" (Halldór Hermannsson,

"Modern Icelandic,” Islandica, 1919, 12:17, 43).

68. Iceland was colonized mainly by Norwegians, and Greenland in turn mainly by Icelanders. Formal rule over these two islands by the king of Norway began in 1261-62. In 1397 a merger of the crowns of Norway and Denmark placed in Danish hands control over Norway's possessions, Iceland and Greenland. Iceland was declared independent during World War Il, in 1944, after Nazi Germany had

overrun

Denmark,

but Greenland

remains

a Danish

colony

to this day. What,

Kepler’s Notes on the Dream

46

possessed the customs and language of the Teutons two hundred

years ago,9? as is made clear by the reports of a certain shipwrecked Venetian merchant.” 24, 27. Rarely fewer than ten, sometimes as many as thirty;" he used to train them in the manipulation of various instruments for observing the heavenly bodies,” in making drawings, computathen, did Kepler have in mind in saying that about

1520, a century before he

wrote Note 23, the Norwegians controlled Iceland and Greenland? At that time the Norwegians themselves were dominated by Denmark; in Iceland the Lutheran

Reformation was being introduced from Denmark; and in Greenland the colonists

were being absorbed by the Eskimos den City, L.I., 1942, Ch. 10).

(see Vilhjalmur Stefansson, Greenland,

Gar-

69. Even before the Norwegians migrated to Iceland in the ninth century, they had already settled in the Orkneys, see Hugh Marwick, Orkney (London, 1951),

pp.

37-39.

The

speech

of these

settlers

still survives

in the

Orkneys

as the

so-

called Norn dialect. The Norwegian language, customs, and laws were already being displaced by Scottish at the time mentioned by Kepler, two centuries before

he wrote this note (see Joseph Storer Clouston, A History of Orkney, Kirkwall, 1932, pp. 279-81). Buchanan’s long-lived fisherman, whom Kepler blessed with children, as we saw above in fn. 58, was an Orcadian. 70. Presumably this shipwrecked merchant of Venice is Antonio Zeno, whom Kepler mentions by name in Note 97 on his translation of Plutarch’s Moon (Somnium, 1634 ed., p. 170; Frisch, VIII, 120:20). A book about the alleged adventures

of Antonio and his brother Nicoló Zeno, a century before Columbus, was published at Venice in 1558. "In its early days it was practically misleading, deceiving such

navigators

as Frobisher,

Davis, and

Hall, and

helping

nobody;

whilst

later days it had the effect of throwing the cartography of the North

in its

Atlantic

into confusion for some two hundred years” (Frederic W. Lucas, The Annals of the Voyages of the Brothers Nicoló and Antonio Zeno, London, 1898, p. 56). This

ingeniously mischievous book about the Zeno brothers fooled the two leading geographers, Mercator and Ortelius, whom Kepler trusted. Consequently he misinterpreted Plutarch to be talking about a voyage to America in antiquity, as we saw in fn. 5, above. However, the Zeno concoction does not mention the Orkneys. Kepler’s statement about them may have been based on one of the numerous unavailing attempts to identify the fabulous Zenonian islands with actual places in the North Atlantic. 71. Appendix G cites a list of Brahe’s students that is numbered from one to thirty-two. But these thirty-two students were not all with Tycho at the same time. Nor is the list complete. It was supplemented by Dreyer (Tycho Brahe, pp. 383-84), who added sixteen more names, including Longberg (whose Astronomia

Danica was quoted in fn. 61, above). Longberg and other students of Brahe were discussed by Dreyer in Tycho Brahe, pp. 117-27. One of the points of difference between the Dream’s fictional character, Duracotus, and his creator, Kepler, is that the former learned astronomy from Brahe,

whereas the latter was already an accomplished astronomer when Tycho. Kepler was not a pupil of Tycho, but rather an assistant. 72. Brahe

described these instruments in his Astronomiae

he first met

instauratae mechanica

Kepler’s Notes on the Dream

47

tions, chemical experiments, and similar scientific studies.

25. Being in control of his own wealth and having inherited a

large fortune, he spent liberally for research.

Moreover,

he con-

quered all feelings of fatigue and tirelessly pursued objectives generally regarded as unattainable. This is shown by his highly precise method of observation, in which he fought against the very nature

of human vision and emerged victorious. 26. One of this man’s amusements was sometimes, when people

were leaving the island to whom

he had already said goodbye, to

upset their plans with an unexpected boatmen’s strike and detain them longer than they wished, unless any of them had learned how to fly. [27. See Note 24.] 28. At that time I was engaged in reading Martin del Rio's work on Investigations of Magic.? And I knew Vergil’s verse: "In(Wandsbek,

(Stockholm,

1598). This work was reproduced in facsimile by photolithography 1901);

reprinted

in

Tychonis

Brahe...

opera,

V,

3-162;

and

its

most important sections were translated into English as Tycho Brabe's Description of His Instruments and Scientific Work

(see above, fn. 66).

studied

in 1609, however,

73. If we could determine when Kepler “was engaged in reading" Rio, we would have an additional clue to help us fix the time when he composed the text of his Dream. His earliest references to Rio occur in letters which he wrote in 1606 and 1607 (Gesam. Werke, XV, 358:42-43, 454:183-84). But these references suggest that in those years Kepler consulted Rio’s volume occasionally rather than it systematically.

The

situation

was

quite

different.

In

that year Kepler wrote two books dealing with the subject of astrology. He composed the second one in the closing months of 1609, and dated the dedication January 3, 1610. In this dedication he commented on Rio’s treatment of an astrological theme in such a way as to imply that he had been scrutinizing the book carefully

(Gesam. Werke, IV, 151:7-8). Moreover, in the body of the book (ibid., 201:1821), Kepler quoted from Rio without mentioning him by name, although he did so later when using the same material in Note 220 on the Dream. In November, 1610,

Kepler was asked to lend his copy of Rio to a friend (Gesam. Werke, XVI, 344, No. 598). All this evidence points to 1609 as the time when Kepler “was engaged in reading" Rio. Kepler cited him again in a work written in 1615 (Gesam. Werke,

IX, 206:11)

and also, as we

just saw, in Note

220.

Although Martin Antony del Rio (1551-1608) is almost completely forgotten today, his great influence on his contemporaries can be inferred from Kepler’s frequent references to his Investigations of Magic (Disquisitionum magicarum libri sex, Louvain, 1599-1600). This collection of weird tales and malicious lies was

intended by the author, who was a lawyer and administrator, to be a guide for prosecutors of alleged witches. Its veneer of superficial erudition and pretended moderation covered the most callous brutality toward accused persons in countless cases. It is dificult to conceive

how

much

harm

was

done

to innocent, unfortu-

nate, and helpless people by this monstrous work, which was reprinted again and again for nearly a hundred and fifty years. Its author was a Jesuit, who for a time

Kepler’s Notes on the Dream

48

cantations can even bring the moon down from heaven.” ™

The region of the sky was eminently appropriate. For when the moon is full for other people, it is frequently invisible in Iceland.*? Writers say that magic is common among the people of the north,”® and it is credible that those spirits of darkness lie in wait taught theology in the University of Graz. This institution was founded in 1586 bv Catholics

the

to combat

employed

later

which

school

Lutheran

That

Kepler.

in Graz,

triumphed

school was closed when the Catholic Counter-Reformation

and Kepler had to leave the city and district because he refused to become a Catholic. 74. Eclogues, viii.69. Vergil was required reading in the school curriculum of

Kepler's time. But Kepler's knowledge of Vergil was undoubtedly extended after

he went to Graz. For, although he was hired to teach mathematics

there, he had

only a few pupils the first year, and none at all most of the second year. The

school authorities decided that Kepler was not to be blamed for this situation, since *. . . the study of mathematics is not for everybody .... However, lest he receive his pay for nothing, we have ordered him . . . to give instruction to the

upper classes" in other subjects, "including Vergil" Neumann, and C. Gruner, 687:11-4 up).

Kepler

(Gesamt.

admitted

Werke,

Jobannes

that he was

XIII, 287:64-67,

Kepler,

then

Stuttgart,

onlv

68-72).

On

curriculum,

graphic

Mystery

assisted

as I was

Reitlinger,

1868, p. 216; Frisch,

slightly familiar the other

“I had no difficulty understanding the geometry

school

(Edmund

by

diagrams,

impressed

Europe's

with

hand,

calculations,

and

VIII,

trigonometrv

elsewhere

and astronomy

C. W.

he said:

offered in the proportions"

(ibid., IIT, 108:11-13). And the knowledge of astronomy displayed in his Cosmoof

1596

so

foremost

astronomer,

Tycho

Brahe, that he eagerly sought Kepler as his assistant. 75. People who live near the Arctic Circle may be unable to see the full moon when

it is visible to those in lower latitudes. The

reason for this phenomenon

is

that the moon’s orbit about the earth is tilted about 5°. When the moon dips way

down, it does not even rise one or more days in the month for those in the higher latitudes. At such times they will not see the moon, even though it is full for those

in lower latitudes. On the other hand, when the moon reaches its greatest possible

declination, it does not set for a whole day or more for those in the higher latitudes. 76. One such writer was Olaus Magnus (1490-1558), whom Kepler mentions by name in Note 39. In his History of the Northern Peoples (Historia de gentibus septentrionalibus, Rome, 1555), Magnus referred to the proficiency of the “artem

magicam apud septentrionales populos”

(Bk. 3, Ch. 15, p. 117). These words may

well have been the model for Kepler's remark, onalibus populis magiam familiarem.

here in Note

28, about septentri-

From Magnus, Kepler evidently derived the additional idea of locating the en-

trance to Purgatory "in the earth beneath Mt. Hekla, the Icelandic volcano"

(see

Kepler's Note 2). Magnus had referred to an Icelandic rock or ridge "which, like Etna, boils with perpetual fires; and there is believed to be the place of punishment and expiation for besmirched

souls"

(History

of tbe Nortbern

2, Ch. 3, p. 62). Alongside this passage, the abridgment 1599,

p.

39)

put

the

following

explanatory

sidenote:

of Magnus

“The

Peoples, Bk.

volcanic

(Hamburg,

mountain

Kepler’s Notes on the Dream

49

for those long nights. Iceland is in fact buried deep in the north. It is also undoubtedly true that the leisure due to the dim light and the unbroken nights are conducive to philosophy. This is confirmed by Julius Frederick, the most illustrious duke of Wiirttemberg. On a memorable trip * he traveled also through the north, where he says men are found far and wide who are remarkably learned and impart their philosophy to strangers with an elegance rare among us. 29. I deemed this season of the year the most suitable for the voyage from that harbor in the kingdom of Denmark to Iceland. 30. Ihis follows from Note 13, in accordance with spherical astronomy. 31. Refer back to Note 28. 32.

A charioteer dreams about a carriage,

A judge about a legal fight.

The wealth you seek by day,

You acquire at night. 33. The aforementioned bishop assured Tycho Brahe that the people of Iceland are extremely intelligent. which is believed to be the purgatory of souls." Kepler's use of the words montis . ignivomi to describe Mt. Hekla as the site of Purgatory strikingly echoes the

terminology of the abridgment of Magnus. This was translated into English under

the title A Compendious History of the Goths, Swedes, and Vandals, and Other Northern Nations (London, 1658). Magnus, a bishop of the Roman Catholic

church, was interested in pinpointing some plausible entrance on earth to the im-

aginary fires of Purgatory. The volcanic activity of Mt. Hekla in Iceland naturally

commended itself for this purpose to Magnus, whose diocese was Upsala in Swe-

den. His History

of the Northern Peoples was undoubtedly one of the “histories”

cited in Kepler’s Note 12 as testifying to the flames at the summit of Mt. Hekla.

77. This trip lasted two years, and ended in March or April, 1616, according to the archivist Christian F. Sattler, Geschichte des Herzogtbums Wurtenberg unter der Regierung der Herzogen (Ulm and Tübingen, 1769-83), VI, 101. But elsewhere Sattler says (V, 282) that the duke came back from the wars late in September, 1614, so that his northern trip could not have lasted two full years; indeed

Sattler here dates the beginning of the trip in 1616. An engraved portrait of Duke

Julius Frederick (1588-1635) forms the frontispiece of Sattler’s Vol. VIII. Since the duke did not take the trouble to write down the impressions made on him by

his trip, his observation concerning the high intellectual attainments of the northerners must presumably have reached Kepler by word of mouth. Kepler was on

excellent terms with high officials of the Wurttemberg court at Stuttgart, where he spent a good deal of time in connection with his mother’s trial (Frisch, VIII,

551:13-16). In 1615 Duke Julius Frederick’s younger brother, Frederick Achilles

(1591-1631), published a volume which was placed on the Roman church’s Index of Prohibited Books by the same decree that suspended

cus’ Revolutions “until corrected” (see fn. 34, above).

Catholic Coperni-

50

Kepler s Notes on the Dream 34. These spirits are the sciences in which the causes of phenom-

ena are disclosed. This allegory was suggested to me by the Greek

word

know,”

Daemon,’®

as though

which

is derived

it were daemon.

from

Having

daiein,

made

meaning

“to

this substitu-

tion, now read Note 28 from “It is also undoubtedly true... .” 35. The real reason for the number escapes me. Was I thinking of the nine Muses, because in pagan belief they too are divinities, which is what I mean by "spirits"? Or did I take up into that num-

ber the following subjects:

1. metaphysics, 2. medicine,

3. ethics,

4. astronomy, 5. astrology, 6. optics, 7. music, 8. geometry, 9. arithmetic?

36. I am sure that here I had in mind either Urania among the

Muses or astronomy among the sciences. For if the northerners were not deprived of many aids to their life on account of the cold, I should say that they are better suited for astronomy than others, because among them there are greater differences between day and night, and these are phenomena conducive to astronomy.

37. If this was said about the Muses, the others are charged with

some dishonesty. But if it was said about the sciences, medicine gives instruction about poisons, too, and, when it is practiced indiscreetly, it even spawns alchemists; metaphysics absurdly exagger-

ates its goals, and with its excessive and troublesome subtleties con-

fuses teachings accepted everywhere; ethics recommends loftiness,

78. According to the religious beliefs of the ancient Greeks, a daimon was a minor divinity, intermediate between the great gods and human beings; it is in this sense that Kepler, half-seriously and half-jokingly, in the next section of the

Dream

speaks about the Daemon

from

Levania. But this term was understood

by

many of Kepler’s uninformed contemporaries to mean an evil spirit. Where Kep-

ler had Duracotus’ mother invoke a Greek-like lesser divinity, “minds which were

dark within and suspected everything of being dark” (see Kepler’s thought they saw Kepler’s mother communing with the devil’s cohorts. 79. The Greek word

Note

8)

daemon means "an expert,” “one who knows.” In deriving

Daemon (“minor divinity”) from daemon ("expert"), Kepler followed the etymological speculation of Plato (Cratylus, 398"). The etymology proposed by Plato and accepted by Kepler is rejected by modern philologists, who connect daimon

("the divinity”) with the verb daiomai ("divide"). According to this view, a daimon was so called because he allotted their destinies to mortal men, cutting out their future for them; see Hjalmar Frisk, Griechisches etymologisches Worterbuch (Heidelberg: Winter, 1954——), I, 341. For the Greek concept of daimon, see Herbert J. Rose, Harvard Theological Review (1935), 28:246-49; for the alteration of the Greek daimon into the modern “demon,” see Pierre Chantraine, “Aspects du vocabulaire grec et de sa survivance en Frangais," Académie des Inscriptions et Belles-Lettres, Comptes Rendus (1954), pp. 452-53.

Kepler’s Notes on the Dream

51

which is not beneficial to everybody; astrology supports superstitions; optics supplies illusions; music panders to the passions, geom-

etry to unjust rule, and arithmetic to greed. But the following is a better interpretation. Although they are all gentle and innocuous (hence they are not those vile and apostate spirits who have deal-

ings with magicians and wizards, whose cruel crimes are irrefutably proved

by their own

defender,

Porphyry) ®° nevertheless

this is

especially true of astronomy on account of the nature of its subject. 38. In seeking my reason for this number, I got no further than the discovery that the Latin words for “Copernican Astronomy" *! contain this very number of letters or characters, and that there are just as many kinds of conjunctions of pairs of the plan-

ets, of which there are seven.®? Moreover, it is amusing to add that a pair of cubical dice has the same number of throws. For 21 isa

triangular number

on the base 6.9 The

allegorical evocation is

8o. Porphyry was a Neoplatonist who lived in the third century after Christ. Elsewhere Kepler called him a "philosopher with verv deep insight," both as an interpreter of Plato and as a commentator on Ptolemy’s Harmonics (Gesam. Werke,

VI,

106:40-107:1;

286:1«—17).

In fact, Kepler

thought

so highly

of Por-

phyry's commentary that he undertook to translate it from Greek into Latin, and was half finished when adverse circumstances compelled him to stop (Gesam. Werke, VI, 369:10-17). But Kepler was also familiar with Porphyry's reputation as an “opponent of Christian doctrine" (ibid. 451:31-32). As an adherent of the pagan religion, Porphyry believed in the existence of lesser divinities, whom he divided into two distinct groups, the good spirits and the evil spirits. The loftiness of his ethical conduct and teaching was recognized bv his principal Christian adversary, Augustine, who sinsled him out as the “noblest philosopher of the pagans" (City of God, Bk. 22, Ch. 3). Nevertheless, Augustine denounced Porphyry at great length for his attitude toward the pagan daimon (ibid., Bk. 10, Chs. 9-11, 26-29; Bk. 19, Ch. 23). Kepler's uncomplimentary reference to Porphyry here in Note 37 seems to be based, not on the Neoplatonist's writings, but on Augustine's

denunciation of him. Kepler told Herwart von Hohenburg: "I have begun to read Augustine's City of God" (Gesam. Werke, XV, 300:185-86). In that treatise (Bk.

9, Ch. 20) Kepler could have encountered the false etvmology of datmon which he incorporated in his Note 34. For a recent analysis of Augustine's treatment of

Porphyry's attitude toward the daimon, see John J. O'Meara, Porpbyry's Philosophy from Oracles in Augustine (Paris, 1959), pp. 58, 98. 81. Astronomia Copernicana.

82. Here, in addition to the three outer planets (Saturn, Jupiter, and Mars) and

the two inner planets (Venus and Mercury), Kepler reckoned the earth and the moon, also, as planets, making seven in all. 83. In a mathematical treatise which he did not live to finish, Kepler explained

that "all the triangular numbers are formed by adding to the preceding triangular number the next number in the arithmetical progression as the base" (Frisch, VIII,

52

Kepler's Notes

on the Dream

taken from Del Rio ** and magic, yet it conceals a philological meaning: *he is evoked" is equivalent to “he 1s expressed.” 39. This is mentioned by Olaus and others also with regard to the Finns, a northern people, and their neighbors, the Lapps.*? But

I turned such help into the doctrine of natural days, zones, and

belts, and into the experience of the Dutchmen in the Arctic Ocean,*’ who found everything occurring just as we astronomers

161). For example, start by adding 1 to o, making a triangular number 1. To this, add 2, making the next triangular number 3. To this, add 3, making the next trian-

gular number 6. To this, add 4, making the next triangular number ro. To this, add 5, making the next triangular number 15. To this, add 6, making our triangular

number 21. The number."

accompanying

diagram

will

clarify

the

meaning

The same diagram will show that a pair of dice can produce

of “triangular

21 non-duplicating

throws. Thus, the 6 on one cube can turn up with any number from 1 to 6 on the other cube; this situation 1s represented by the bottom line in our diagram. The

next to the bottom line sets forth the situation for the 5 on the first cube, and so

on. In like manner, the outermost planet can be in conjunction with anv one of the six remaining planets; this is the situation represented bv the bottom line.

Then Jupiter can be in conjunction with five other planets, and so on. 84. See fn. 73, above. 85. Olaus Magnus did not say that the Finns and Lapps whisked people “in an instant to other shores.” But the bishop did say that “the Finns in former times used to... offer winds for sale ...to merchants; . . . of the three magical knots, . . . by opening the first knot, the merchants would obtain gentle winds; the second knot, stronger winds; and the third knot, most violent winds" (History of the Northern Peoples, ed. 1555, Bk. 3, Ch. 16, p. 119; abridgment, 1599, p. 117; English translation, 1658, Bk. 3, Ch. 15, p. 47). Presumably it was the bishop’s legend about bottling up very violent winds that Kepler had in mind when he talked about instantaneous transportation. Kepler's reference to "Olaus and others" in-

cludes Del Rio, who

quoted

the bishop's legend

in his own

Magic, Bk. 2, question 11 (ed. 1635, p. 137 C-D). 86. “Flow many meanings does the word ‘day’ have

among

Investigations

astronomers?

of

Two

principal meanings. For either it means . . . the interval of time within which day occurs once and night occurs once, and that is usually called the ‘natural day’; or ‘day’ is taken as the opposite of night, or more precisely, the time when the center of the sun is above the horizon, and that is called the ‘artificial day’” (Kepler,

Epitome; Gesam. Werke, VII, 179:6-10). 87. For the experience of the Dutchmen, see fn. 22, above.

Kepler's Notes on the Dream

53

here at a distance have known and taught now for many centuries. 40. My previous remarks concerned places on the earth which man can approach. What I say now should be applied to the heavenly regions. 41. There is a popular joke: "Tl believe it rather than go into the matter personally." And many people ask whether we astronomers have just fallen down from heaven. They were answered by Galileo's Sidereal Message °® more in line with his own ideas. But even stronger is the judgment

of reason, being testimony

which

prevails over every objection, as the Dutchmen found by experience in their winter sojourn, Note 39.

42. “Moon” in Hebrew is Lebana *? or Levana. I could have called it “Selenitis,” but Hebrew words, being less familiar to our ears, inspire greater awe and are recommended in the occult arts. 88. The Sidereal Message was the earliest book to describe astronomical observations made with a telescope; complete English translation by Edward Stafford Carlos (London, 1880; reissued, London: Dawson, 1960); incomplete paraphrase in Drake, Discoveries and Opinions of Galileo, pp. 21-58.

“Kepler is said to have provided a German

Prague,” according to Ginther

(Traum,

edition of it, which

p. ix). In fact, however,

appeared

in

neither Kepler

nor anybody else ever provided a Prague edition of Galileo’s Sidereal Message,

either in German

or in the Latin of the original edition

(Sidereus nuncius, Venice,

1610). This bibliographical ghost—the supposed Prague edition of Galileo’s Sidereal

Message—appeared for the first time early in the nineteenth century. It arose from a misunderstanding of the title of Kepler’s prompt reaction to Galileo’s epochmaking little book. The word nuncius in Galileo’s title was taken by Kepler in his haste to mean “messenger.” Hence he entitled his reaction A Conversation with the Sidereal Messenger (Dissertatio cum nuncio sidereo, Prague, 1610). But those

who saw only this title and had no opportunity to examine the book itself assumed that Kepler had nuncius. Hence Sidereus nuncius. Wohlwill, "Die 2d series (1887),

published a Dissertatio together with a reissue of the Sidereus they talked about a (purely imaginary) Prague edition of the This confused situation was admirably straightened out by Emil Prager Ausgabe des Nuncius sidereus,” Bibliotheca mathematica, 1:100-102. For the background of Kepler's reaction to the Szdereal

Message, see Edward Rosen, “Galileo and Kepler: Their First Two Contacts,” Isis (1966), 57:262-64. 89. The misprint

Lbana

in the

1634 Somnium

was

corrected

by

Frisch

(VIII,

44). As a student of theology at Tubingen, Kepler studied Hebrew, receiving ex-

cellent grades (Reitlinger, Neumann, and Gruner, Kepler, p. 210). His professor of Hebrew was Georg Weigenmaier (1555-99); see Christian Friedrich Schnurrer, Biographische und litterarische Nachrichten von ehmaligen Lehrern der hebräischen Litteratur in Tubingen (Ulm, 1792), pp. 136-49, and Reitlinger,

Neumann, and Gruner, Kepler, p. 86. For Kepler’s comparison of his own mental-

ity with that of another of his professors, see Edward Not a Hoe,” Classical Outlook (1966), 44:6-7.

Rosen, “Kepler’s Rake Was

54

Kepler’s Notes on the Dream 43. Here again my very assumptions necessarily cast me up on

the shore which Plutarch picked out, since he, too, mentioned the

return of Saturn to the Bull?" But the steps leading up to my

choice were as follows. I adopted the practice of the astrologers ?!

in putting both the sun and the moon in their own

dignities.”

However, the sun was in the Lion, its own house,” before Duracotus returned home. Had this not been the case, the sun could have been placed in that sign, with the waning and crescent moon in the Crab, which in like manner is its house.?* But the following inconvenience was involved: I had to locate the sun below the eastern horizon, because night is more appropriately selected 9o. Plutarch, Moon, 941C; Kepler’s translation in the 1634 Sommium, p. 171, or Frisch, VIII, 99:16-18. In Note 100 on this passage in his translation of Plutarch, Kepler exclaimed: “See how my Dream coincided completely in detail, at a time when I had not even dreamed about this little book by Plutarch” (1634 Somnium, p. 171; Frisch, VII, 120). Since Kepler first encountered Plutarch’s Moon in 1595,

this section of the Dream would have formed part of his 1593 lunar dissertation. But “my first traces of a trip to the moon, which was my aspiration in later times,” Kepler said he found in Lucian’s True

after Plutarch, apparently around

1604

Story. He

(see Kepler’s Note

decade or so earlier, in the lunar dissertation

came

across that work

2, above). Hence,

of 1593, there would

have

been

a

no

trip to the moon, either when Saturn was in the Bull or under any other astrological auspices. In other words, Kepler's statements in his Note 2 on the Dream and in Note

100 on his translation of Plutarch are inconsistent with each other. Note

2

on the Dream was written about 1622 (see fn. 28, above), when Kepler was giving

his full attention to the Dream and its development. On the other hand, Note roo in the Moon was composed in 1630 (Introduction, p. xxi, above), long after the Dream had receded into the background. In this conflict of testimony, conse-

quently, Note 2 on the Dream should be accepted in preference to Note

100 on

the Moon. 'Thus, if the foregoing reasoning is sound, in Kepler's lunar dissertation Of 1593 there was no trip to the moon; that post-Lucianic feature was added in 1609; and Note 100 on the translation of Plutarch was due to a faulty recollection,

despite Kepler's confident assertion that “with my quite reliable memory I recall the origins of the individual parts of my tale" (Kepler's Note 2, above). For Kepler's admission in 1628 that he was losing his memory,

see fn. 366, below.

91. Kepler believed in astrology, within certain limitations; see for example, fn.

105, below. He told Mastlin: “As a Lutheran astrologer, I discard the nonsense, but retain the substance" (Gesam. Werke, XII, 184:177-78).

92. A dignity was a position which enhanced a planet’s influence.

93. Ihe

astrologers regarded

the sign of the Lion

as the house

of the sun.

94. The astrologers regarded the sign of the Crab as the house of the moon: “The sign of the Lion, being masculine, was assigned to the sun as its house, but the sign of the Crab, being feminine, to the moon"; see Ptolemy, T'etrabiblos, 1.18 (Opera, III, 1, eds. Franz Boll and 5); ed. and tr. F. E. Robbins, Loeb University Press, 1948), p. 79.

Emilie Boer, Leipzig: Teubner, 1940, p. 39:3Classical Library (Cambridge, Mass.: Harvard

Kepler’s Notes on the Dream

55

for those proceedings. On account of these difficulties I deleted the sign of the Crab, and abandoned the year when Saturn was in the Crab, namely, 1593,” the year in which that discussion of the

moon was written by your hand, Besold.?* These erasures I still find in my first copy.?' On the other hand, for my Duracotus, af-

ter he spent the winter in his own country, I chose March, with the

sun at the equinox, a good astronomical sign, and at the entrance to

its exaltation in the Ram.?? Hence, if the moon was required to appear in its crescent phase, that 1s, in a sign next to the sun, it had no

dignity in any other sign but exaltation in the Dull?? Consequently, to enable it to be seen near other heavenly bodies, I had to bring the sun back below the western horizon at the onset of night. This was what I wanted, especially in the slowly descending signs.

When

the moon

occupies such a position in them,

it 1s

very conspicuous, with its entire mass embraced by its bright crescent, as I described it in the Optics, in the Conversation with tbe Sidereal Messenger of Galileo, and finally in the Epitome? 95. This was the year first chosen by Kepler in 1609 for his Levania episode.

96. The hand was Besold's, but the mind was Kepler's (see Kepler's Note 2). 97. "My first copy" of the 1593 dissertation, by contrast with that other "first

copy” of the expanded 1609 version, which had been taken from Prague in 1611 (see Kepler's Note 8). 98. According to the astrologers, a planet had its exaltation in the position

where it exerted its maximum influence; this was the Ram, in the case of the sun. “When the sun is in the Ram, it is crossing over into the upper, northern semicircle .... Accordingly, the sun has been allotted the Ram as its exaltation,

where it begins to make the day longer and its natural heating effect more intense” (Ptolemy, Tetrabiblos; eds. Boll and Boer, p. 43:11-16; ed. and tr. Robbins, p. 89). 99. In astrological doctrine, the moon had its exaltation in the sign of the Bull (Ptolemy,

T'etrabiblos; eds. Boll and Boer, p. 44:2; ed. and tr. Robbins, p. 89).

100. This is pre-Copernican thought and language, according to which the earth has no daily rotation. Instead, six signs of the zodiac rise each day, the other six by night. On two days of the year (the equinoxes) the six daytime signs take exactly as long to rise or set as do the six nighttime signs. But during the six months between the autumnal equinox and the spring equinox, when the nights are longer

than the days, the six signs visible at night set (or descend)

more

slowly than the

six daytime signs. 101. “At the time of the crescent moon, a light is seen diffused over the entire body adjoining the horns”; this passage in the Optics (Gesam. Werke, II, 15) was quoted by Kepler from Mästlin’s Disputation concerning Eclipses Sun and Moon (Tübingen, 1596), Thesis 21. In the Conversation, which took the form of an open letter to Galileo, said: "No less ingenious is your arrangement . . . for inspecting the disk moon when its horns first emerge. You explain how to observe from behind

223:14of the Kepler of the a roof

56

Kepler’s Notes on the Dream

Hence, in order to have Saturn, too, in conjunction with the moon, a conjunction regarded by the astrologers as the basis of the occult arts, Saturn, also, had to be put in the Bull. Thus the time turns out to be in the period when Tycho’s observations were most numer-

ous?

the

evening

of March

1:1/21,?

1589,°°*

when,

more-

over, the conjunction occurs in the constellation of the Pleiades. When this group is located in the vicinity of the moon, it enlivens so that the horns are covered up and the rest of the disk becomes visible. This is an observational method very familiar to me” (Rosen, Kepler’s Conversation, p. 32). “The faint light seen adjoining the bright horn of the crescent moon on the side turned away from the sun” is the subject of the third question from the end of Sec. 2 of Pt. 5 of Bk. 6 of Kepler’s Epitome of Copernican Astronomy. This thor-

ough introduction to the science in the form of questions and answers appeared in

installments. Kepler published the first three of the Epitome’s seven books in 1618, and the fourth book in 1620, at Linz; he issued the last three books at Frankfurt/ Main in 1621. Bks. 4 and 5 of the Epitome were translated into English by Charles Glenn Wallis in Great Books, Vol. 16, pp. 839-1004. 102. Tycho Brahe’s improvements of astronomical instruments, his insistence on

systematic as opposed to occasional observation, and his stress on accuracy conferred on his results a high value, of which he was acutely conscious. But he never published his observations, because he was afraid someone else to construct the cosmic system which

that they might be used by he himself longed to produce

as the crowning achievement of his life’s work. After his death, his “Treasury of

Observations” passed into Kepler’s hands. This access to Brahe’s observations permitted Kepler to discover his laws of planetary motion, and to publish his Rudolphine Tables. But Kepler never published Tycho's observations themselves. Vari-

ous excerpts were printed on several later occasions, but the definitive edition was the work of Drever, who resigned as director of the Armagh Observatory in

order to be able to devote all his time to the completion of this task, which was of

very great importance to astronomers in many

ways. The

finished product fills

Vols. 10-13 of Tychonis Brahe . . . opera. The fourth and last volume of Brahe's "[reasury of Observations" was sent to the press by Drever not long before his death on September 14, 1926.

As long as Kepler had exclusive control

Brahe's observations were

most numerous

of the “Treasury,”

in March,

1589, could

his remark

that

not be refuted.

Perhaps Kepler intended his remark less as a comment on Brahe's career as an observer than as a device for heightening the emotional impact of this passage in his Dream. If so, Kepler's purpose here would be like his motive in altering the description of Hven (see above, fn. 66). 103. The reformed calendar promulgated by Pope Gregory XIII in 1582 omitted

ten days. Hence, those countries which refused to accept the new Gregorian calendar found their old Julian calendar ten days ahead of the new Gregorian calendar. As a careful writer addressing readers in both groups of countries, Kepler used both the Julian and Gregorian numbers for the same dav. 104. In 1609, when Kepler decided that he wanted Saturn in the Bull rather than in the Crab, he had to abandon 1593, his first choice as the vear for his Levania episode, and replace it by 1589.

Kepler's Notes on the Dream

57

the imagination of a person born then, as I admitted in the Harmonics. Furthermore, astronomical considerations favor this constellation for observing the crescent moon. See the observation

of this sort in my Optics, Chapter 11, page 347,'° for April 8 and July 27, 1598.!** 44, 46, 47. This also is a magical ceremony. The corresponding

feature in the teaching of astronomy is that the method is not in the least voluble or spontaneous. On the contrary, every prompt answer requires repose, recollection of ideas, and set words. During those years in Prague ''? I often carried out a special procedure in connection with a certain observation. Whenever men or women came together to watch me, first, while they were engaged in conversation, I used to hide myself from them in a nearby corner of the house, which had been chosen for this demonstration. I cut out the daylight, constructed a tiny window out of a very small opening, and hung a white sheet on the wall. Having finished. these preparations, I called in the spectators. These were my ceremonies, these my rites. Do you want characters too? In capital letters I wrote with chalk on a black board what I thought suited the spectators. The shape of the letters was backwards (behold the magical rite), as Hebrew 1s written. I hung this board with the letters upside down in the open air outside in the sunshine. As a result, what

I had written was projected right side up on the white wall within.

If a breeze disturbed the board outside, the letters inside wiggled to and fro on the wall in an irregular motion.

45. Those of my above-mentioned spectators who are still alive

will see, when they refresh their memory, what that crossroads was

105. Kepler’s Harmonics of the Universe (Linz, 1619), which he dedicated to King James I of England, contains his third law of planetary motion (Gesam. Werke, VI, 302:21-23). In Bk. 4, Ch. 7, of the Harmonics he mentioned that the

moon was “very close to the Bull’s eye” at the time of his birth, and he added that

“when the gibbous moon is in the bright constellation of the Bull’s face, it fills the

imaginative faculty of the soul with fantasies, many of which I have nevertheless actually found in agreement with the nature of things” (Gesam. Werke, 279:8-9, 280:1-4). “The bright constellation of the Bull’s face” 1s the Hyades,

VI, not

the Pleiades, which are less bright and in the Bull’s tail, not face. Bk. 5 of the Harmonics was translated into English by Charles Glenn Wallis in Great Books,

Vol. 16, pp. 1005-85. 106. The misprint

44).

107. Gesam.

"247"

in the

Werke, II, 297: 10-25.

1634 Sommnium

108. Kepler lived in Prague from 1600 to 1612.

was

corrected

by Frisch

(VIII,

58

Kepler s Notes on the Dream

in my house. But here and now the astronomical crossroads is per-

ceived in the assumed heavenly pattern. And this is a double roads. The first is the location of the sun at the equinoctial where the equator and the sun's ecliptic path intersect each Brahe's manuscripts contain an observation made on that the altitude of the sun in the equinoctial point. The crossroad is the moon's descending node or dragon's tail,’*°

crosspoint, other; day of second which

was then at the end of the Water Bearer. The astronomer must pay

attention to this tail in order to know when the moon is at its limits.!!! For instance, it was then at its southern limit in the end of the Bull, a lunar position which invites astronomers to observe the latitude of its limits.

[46, 47. See Note 44.]

48. I used to tack on these very games too, which the spectators enjoyed all the more for realizing that they were games. 49. With this very rite (ha, how magically magical!), shortly before I conceived the plan of this book,!? we had observed a

solar eclipse on October 2/12, 1605.!? You remember, O envoys!!* from the Count Palatine of Neuburg,!? because you were present. For on the balcony of the pavilion in the emperor's 109.

T ycbonis

Brabe.

. . opera, XI,

317, left-hand

column,

second

observation.

110. The descending node or dragon’s tail is the point on the ecliptic where the

moon crosses from north latitude to south latitude. i11. "Ihe points on the ecliptic which are at a quadrant's distance from the nodes are called the ‘limits’ . . . because, when the planet reaches those points, it does not diverge any farther toward the sides, but turning back from those points it begins to return toward the ecliptic" (Kepler, Epitome; Gesam. Werke, VII,

394:40-43).

112. Kepler conceived the plan of the Dream in the closing months

of 1605. But

three and one-half years passed before he put his planned conception down paper in the summer of 1609. 113. Concerning this phenomenon

(Oppolzer,

Canon

of Eclipses,

p.

on

268, No.

6674), Kepler published a Letter about tbe Solar Eclipse Which Occurred in This Year 1605, in the Month of October (Prague, 1605; Gesam. Werke, IV, 37-53). 114. Who were these envoys? Kepler's son Ludwig (see Appendix B) was born

some two years after this solar eclipse. According

to Kepler's memorandum

con-

cerning Ludwig's baptism, one of the infant's "godfathers was the ambassador, Dr. Johann Zeschlin, in the name of the Counts Palatine of Neuburg, the illustrious

prince Philip Ludwig, the father, and Wolfgang William, the son" (Frisch, VIII, 775-76). In the early months of 1605, Zeschlin was one of three envoys sent by the Count Palatine of Neuburg to various courts (Briefe und Akten zur Geschichte des dreissigjährigen Krieges, Munich and Leipzig, 1870-1918, I, 434-35).

But in October, 1605, Count Wolfgang William himself went to the imperial court

Kepler's Notes on the Dream

59

at Prague. Was he accompanied by Zeschlin at that time, and was Zeschlin one of the envoys addressed by Kepler here in Note 49? Zeschlin published two polemical legal treatises in support of Neuburg’s territorial claims (De tutela electorali, Lauingen, 1613; Vindiciae tutelares, Cologne,

1614), and rose to be Neuburg’s vice-chancellor and chief chancellor (J.S. Rauschmavr, “Lauinger Buchdruck," Kollektaneen-Blatt, Jahresschrift des Heimatvereins für den Bezirk Neuburg a. d. Donau, 1938, 102:102-4). To justify his

conversion to Roman Catholicism in 1617, after having been a Lutheran for half a

century, Zeschlin issued an Apologia pro sua fidei professione (Neuburg, 1625); extensive extracts from this defence of his proclamation of his faith were translated from Latin into German by Andreas Rass, Die Convertiten seit der Reformation (Freiburg im Breisgau, 1866-80), IV, 343-404. Zeschlin was born at Kalteneck

near Schwemmingen in Württemberg, and died in Vienna on May 2, 1639, at the

age of seventy-three. 115. Wolfgang William, Count Palatine

(1578-1653), had his capital at Neuburg

on the Danube. Having cast the count's horoscope in 1603, in the following year Kepler presented the count (Gesam. Werke, XV, 77) with a copy of his Forecast

for tbe Year 1605, together with a Thorough Report on an Unusual New Star (Frisch, I, 451-78). When the count acknowledged receipt of the presentation

copy, he thanked Kepler with a gift of money, reported some of his own observations, and asked for additional astrological assistance

(Gesam.

Werke, XV, 92-93).

Replying that he had received the ten ducats, Kepler sent the count a long letter,

dealing partly with

the new

star and

partly with the astrological

question

raised

by the count (ibid., 161-68). The latter answered briefly (ibid., 178). In a massive communication addressed to David Fabricius (see Appendix K), Kepler described

the location of some of the planets when “Wolfgang William, son of Philip Ludwig, Count Palatine of Neuburg, was born” (Gesam. Werke, XV, 273:1320-21; cf. XIV, 415:240), and also referred to “Wolfgang William, Count Palatine, who

hopes to succeed to Jiilich-Cleves” (XV, 240:8-9). In his effort to assert his right

to inherit this territory, then ruled by a mentally deranged and childless duke, Count Wolfgang William spent the months of October and November, 1605, at

the imperial court in Prague; “every day I had to go to the Count Palatine, who treated me honorably and generously,” Kepler wrote to Herwart von Hohenburg on January 13, 1606 (Gesam. about the Solar Eclipse came

Werke, XV, 298:120-21). When Kepler’s Letter from the press in December, 1605, he sent three

copies to the Count Palatine of Neuburg Palatine, the father, Philip Ludwig

(Gesam. Werke, IV, 424). Both Counts

(1547-1614), and the son, Wolfgang

William,

in 1607 agreed to become godfathers of Kepler’s son, Ludwig (see above, fn. 114). In a letter written in 1618 Kepler recalled Wolfgang William’s recent conversion to Catholicism and his expulsion of Protestant ministers and teachers from

Neuburg

(Gesam.

Werke, XVII, 285:63-64; 496). On February 6, 1623, Kepler’s

Discourse on the Great Conjunction or Meeting of Saturn and Jupiter in the Fiery Sign of the Lion, which Occurs in the Month of July in the Year 1623 (Linz, 1623) was dedicated to “Wolfgang William, Count Palatine of the Rhine, Duke of Bavaria, Jülich, Cleves, and Berg,” etc. (Frisch, VII, 687). In this dedication Kepler mentioned his recent pleasant visit to the count’s court at Neuburg. The correspondence between Wolfgang William and Kepler was discovered in the secret archives at Munich by Georg M. Jochner (Historisch-politische Blatter

für das katholische Deutschland, 1908, 141:153-68). A portrait of Wolfgang William was reproduced photographically in Neuburg,

die junge Pfalz und ibre Fur-

60

Kepler's Notes on the Dream

gardens !5 we lacked a dark room. Therefore we covered heads with our coats and kept out the daylight in that way.

our

50. It is not impossible, I believe, with various instruments to re-

produce individual vowels and consonants in imitation of human speech. Yet whatever this is going to be, it will resemble rumbling and screeching more than the living voice. And in this mechanism,

I think, there are built-in traps for the superstitious and gullible, so that they may sometimes suppose demons are talking to them when art is copying magical tricks. And yet in my opinion it is more ap-

propriate for others to assert on a sound basis that anything of this

sort actually happens than for me to deny it without support from any experience of my own.’ Nevertheless, here I am pleasantly reminded of Matthias Seiffart, of blessed memory, my colleague, who was left by Tycho Brahe to his heirs.!!? Seiffart spent three months computing, in accordance

sten: Festschrift zur 450 Jahrfeier der Gründung des Fürstentums Neuburg, ed. Joseph Heider (Neuburg, 1955), pp. 32-33. For the struggle over Jülich-Cleves, see Hajo Holborn, A History of Modern Germany (New York: Knopf, 195964), I, 297-301; or Charles Howard Carter, The Secret Diplomacy of tbe Habsburgs, 1598-1625 (New York: Columbia University Press, 1964), pp. 16-22,

274-76.

116. In a letter dated January 13, 1606, Kepler complained: “. . . the place and my instrument were a whole hour's distance from my home, and with the emptiest promises the workmen kept me waiting right up to the last minute” (Gesam. Werke, XV, 298:111-13). More than a decade later Kepler recalled his observa-

tion "made at Prague in the emperor's pleasure garden amid crowds of courtiers”

and "the bad faith of the gardener, who failed to keep intruders carefully away from the instruments” (zbid., XVII, 162:49-52). 117. Why did Kepler refer to the possibility of a talking machine long before it was actually invented? Undoubtedly his purpose was to suggest that what sounded

like the rasping voice of a spirit might have been only an imperfect mechanical reproduction of human speech. In that case there was no spirit or daemon. To

forestall any demand from his critics that he should point to the existence of such

a device, he disclaimed all personal knowledge, and instead resorted to the convenient strategy of falling back on the assertions of (unnamed) authorities. 118. Matthias Seiffart joined Tycho after Brahe went to Prague in 1599 (Dreyer, Tycho Brahe, pp. 302, 384). In April of the following year, when Kepler and Brahe had their famous quarrel, which almost resulted in breaking up one of the most fruitful partnerships in the history of science, Seiffart was studying with

Brahe. The

latter wrote

on April 8, 1600:

“. . . as soon

as Kepler

left,

I ordered

my student Matthias to copy some things from those papers which I took into my

custody” (Gesam. Werke, XIV, 114:48-49, Tycbonis Brahe... opera, VIII, 299:12-14). When Kepler was appointed to succeed Brahe two days after the latter’s death on October 24, 1601, Seiffart continued his astronomical work with the new Impe-

Kepler’s Notes on the Dream

61

rial Mathematician. In three of his publications Kepler mentions Seiffart's coopera-

tion. In the Optics, for example, he records an observation he made with Seiffart about a month after his appointment (Gesam. Werke, II, 316:9-11). In the New

Astronomy he reports an observation he made in February, 1602 “with the help of the student Matthias Seiffart, who had been left behind by Tycho” (Gesam. Werke,

III, 146:37-39). Finally, in his Singular

Phenomenon,

Kepler

remarks:

“I

had previously forewarned Matthias Sciffart, a student left behind by Brahe, to scrutinize the sun carefully throughout all of these last four days” in the latter

part of May, 1607 (Cresam. Werke, IV, 92:16-17, 94:8-33). During these years when Seiffart was working with Kepler, three of the latter’s correspondents frequently mentioned Sciffart. Fabricius, who had been of great help to Brahe, sent Kepler many long and important letters, in which he often asked

to

be

remembered

to

Sciffart

(Gesam.

Werke,

XIV,

408:215-16,

XV,

101:25-102:26, 127:487-88, 160:103, 196:182, 286:86, 306:118). Another of Brahe's former assistants, Ambrosius Rhodius, wrote that Seiffart would make good any deficiency in the sum of moncy which he was transmitting to Kepler (Gesam. Werke, XIV, 201:6-202:9). He, too, wanted his grectings passed on to Seiffart,

"his very good friend” Gbid., XIV, 444:30-34; XV, 229:25; XVIII, 454:64-65). He

felt hurt when a courier arrived at Sciffart’s expense, but there was no letter from Kepler, "not cven a salutation” (ibid., XV, 203:5-8). Two years later he respect-

fully requested Kepler to urge Sciffart to present himself at Wittenberg University on March

23, 1607, when master's degrees were to be awarded. The only per-

son exempted from the payment of fees would be Sciffart. Acting temporarily as

the dean of the philosophical faculty was the professor of mathematics (ibid., 405:18-22). This mathematics professor, Melchior Jöstel, who also had worked with Brahe, wrote a treatise simplifying the calculations necded to solve certain astronomical

problems. If Jöstel’s treatise (which has survived in handwritten form only, never having been printed) could not be shown to Kepler on account of the objections

raiscd by Brahe’s heirs, “Matthias will be able to do so, because he has all the rules copicd down, but without the proofs” (Gesam. Werke, XVIII, 453:32-34). In compiling some observations for Kepler during a lunar cclipse, Jöstel prepared an additional copy for Seiffart (ibid., XV, No. 346: 10-11). The cordial relationship between Sciffart and Jöstel may explain how Seiffart happened to join Tycho. In September, 1599, Brahe informed Longberg that he was arranging to have two students come to Prague from Wittenberg (Tychonis

Brabe ... opera, VIII, 183:2-4). Although Brahe did not mention their names, he described them as “skilled in trigonometry and computations, and transmitting

their offer through Jöstel.” Since the latter was on excellent terms with Seiffart, who had a copy of his treatise on triangles and coniputations, Sciffart may well have been one of the two students recruited for Tycho’s staff from Wittenberg. In that case he may be the “Matthacus Scifard” of Grossenhain, who was admitted to Wittenberg University on July 30, 1591 (Album academiae Vitebergensis, II, 383). Kepler utilized Seiffart's skill as a computer in connection with the lunar eclipse of April 3, 1605 (Oppolzer, Canon of Eclipses, p. 368, No. 4342; Gesam. Werke, XV, 276:1463; 277:1466-68; 531). Seiffart also served Kepler as an amanuensis, and a manuscript which he copied for Kepler still survives at the Austrian National

Library

in

Vienna

(Gesam.

Werke,

XV,

clearly implics that he carried on astronomical time (ibid., 79:49-50).

135:34-36;

516).

Moreover,

Kepler

discussions with Seiffart for a long

62

Kepler’s Notes on the Dream

with

Tycho’s

precepts,

the

ephemerides

of the

moon

for

one

year.!? He had a voice which could be described in words not un-

like these. He was also affected by depression and mental illness, in which there was no place for relaxation, and he finally died of a

fatal dropsy.'^? 51. Knowledge of the phenomena of the heavenly bodies; from daiein, meaning “to know." !?!

52. Summoned from the moon, toward which our eyes were directed in our imagination."

53. On the sphere of the earth 1° of a great circle is reckoned as

15 German miles. For example, the polar altitude at Rome 1s 41°

50’, and 49° 26’ at Nuremberg on almost the same meridian, there-

fore, from Rome to Nuremberg is 114 miles, and to the bank of the Danube roo miles. Since the polar altitude at Rostock 1s 54° 10’, from Nuremberg to Rostock is 71 miles. Similarly, the polar alti-

tude at Linz is 48°

16’; at Prague, 50° 6’; the difference is 1° 50’,

counted as 26 miles. If 1° contains 15 miles, there will be 860 miles

in the radius of the circle, that is, of the earth’s circumference.!?

But in my Hipparchus '* I prove, and in my Epitome of Coperni119. The year in question was 1603, as we learn from one of Kepler's letters: "When Matthias, in the year 1602, undertook the task of writing the ephemerides of the motions of the moon for the vear 1603, the labor of solving the triangles consumed quite a lot of time" (Gesam. Werke, XV, 137:119-21). 120. In a letter written the year before Seiffart died, Kepler discussed the solar

eclipse of April 9, 1567

(Oppolzer,

Canon

of Eclipses, p. 264, No. 6586), and

re-

called that in his Optics he had followed the calculations of Tycho, “in the handwriting and computations of his student Seiffart" (Gesam. Werke, XVIII, 392:209-10). 121. Kepler's derivation of Daemon (the minor divinity) from daiein (to know) is not accepted by modern philology (see above, fn. 79). 122. The eyes of Duracotus and Fiolxhilde had to be directed toward the moon

in their imagination, because their heads remained covered throughout the Dae-

mon's discourse (Dream, pp. 14, 28-29, above). 123. 360? X 15 = 5400 — 27 = 860 German miles.

124. Kepler never completed the work which

he entitled Hipparchus, or the

Sizes and Distances of tbe Three Bodies, Sun, Moon, and Earth. The unfinished manuscript, formerly at the Pulkovo Observatory and now in the Archives of the

Soviet Academy of Science in Leningrad, was printed by Frisch (III, 520-49). It was begun while Kepler lived in Prague, and was continued after he moved to Linz, the greater part being written in 1616. In 1624 Kepler no longer planned to

publish his Hipparchus

as an independent

rate it in a larger volume

work;

instead, he intended

to incorpo-

(Gesam. Werke, XVIII, 199:64-69). We may therefore

conclude that Kepler's Note 53 was composed before September 9, 1624. In the surviving fragment of his Hipparcbus Kepler gives no proof that the distance

Kepler’s Notes on the Dream

63

can Astronomy Y deduce a priori,'?° that the moon at its apogee is about 59 earth-radii away. Multiplying 59 by 860 yields 50,740

miles.

54. It does not lie; rather, it floats, 1f we consider its resemblance

to an island.'*® But here and now I had to talk about it as it ap-

pears to the eye. For anybody who was on the moon would be

completely place.

convinced

that

the

moon

remains

motionless

in

its

55. Does a physical consideration underlie and blend with the

jocular explanation of the reason why eclipses of the sun and moon bring so much misfortune? There is no doubt that evil spirits are called powers of darkness and of air. You would therefore regard them as sentenced and, so to say, banished to the shadowy regions, to the cone of the earth's shadow. Hence, when this cone of shadow touches the moon, then the daemons invade the moon in a mass, using the cone of shadow as a ladder. On the other hand, when the cone of the moon's shadow touches the earth in a total

eclipse of the sun, the daemons return through the cone to the

earth, as at Note 86, below. But these opportunities are rare. However, to the extent that in this passage the daemon stands for the science of astronomy, there will be seriousness in the assertion that for the mind there is no passage to the moon except through the

earth's shadow and the other things which depend "Shadow Measurement,” a part of my Hipparcbus.??

on it. See

56. If we continue the allegory, it is easy for reason with the

help of shadow measurement to attain knowledge of celestial phenomena. But if we think of the nature of bodies and spirits, again the explanation of the statement is clear. And here, of course, I indulge in a joke: looking straight ahead, I concentrate on physical from the earth to the moon at apogee is about 59 earth-radii, although he does discuss the distances established bv the ancient Greek astronomer, Hipparchus, and by some later investigators of this problem (Frisch, III, 542-43). 125. Gesam. Werke, VII, 279:43-280:45; Great Books, Vol. 16, pp. 876-77.

126. In his Epitome, Kepler set forth his belief that the air's "greatest height barely exceeds the peaks of the mountains; but what comes immediately above the air is the ether, a fine substance which (Gesam. Werke, VII, 53:9-10).

127. "Shadow Measurement”

is diffused throughout

the entire universe"

(or "Sciametry"), the opening section of Kepler's

Hipparcbus, contains definitions, theorems, and problems pertaining ows cast by the earth ond the moon in lunar and solar eclipses

520-33).

to the shad(Frisch, III,

64

Kepler’s Notes on the Dream

reasoning; out to the side, I shoot satirical arrows in all directions at spectators who feel sure of themselves.!?

57. Interpret this physically if the body,

which

has its own

weight, is hurled twelve thousand miles upward in the course of an

hour.?? Take into account also the loss of air (text at Note 71).

If men are deprived of air, they must die like fish deprived of water. For among the conclusions which I accept as approved by the foremost physicists 1s included the assertion that the surface of the air ends at the top of the highest mountains or even lower.!??

58. In the writings of Tycho Brahe insults often occur directed

against men of this kind, who spout philosophy anyway, while he makes the preparations for his labors and night watches.

59. I was thinking of the epigram which I once jokingly aimed

at the bodily build of Mästlin, who was then my teacher:^

128. This minor aspect of the Dream was magnified out of all proportion to its true importance. On account of this exaggeration the Dream was classified as a satire (Introduction, p. xxili, above), and its contribution to the development of science was generally overlooked. 129. Twelve thousand miles an hour would have to be the average speed, since the 50,000 German miles from the earth to the moon are to be traversed in no more than four hours (Dream, p. 15, above). 130. See fn. 126, above. 131. Michael Mastlin (1550-1631), who taught Kepler mathematics and astronomy at Tübingen University, was born in Góppingen. Mastlin liked to sign his M. letters to Kepler with the monogram M. M. M. The four occurrences of the G. letter M stood for “Michael Mastlin, mathematics master" (re. professor), while

G recalled his birthplace,

Goppingen,

which

is about thirty miles away

from

Tubingen (Gesam. Werke, XII, 55:51-53; 381). In the Preface to his Cosmograplic Mystery Kepler stated that Mastlin “in his lectures

used

to make

mention

very

frequently”

of Copernicus

(Gesam.

Werke,

I,

9:14), and that “partly from Mastlin’s utterances and partly from my own reflection I gradually compiled a list of the advantages which Copernicus possesses over Ptolemy from the mathematical point of view” (ibid., I, 9:20-21). In a public disputation at Tübingen

on February

21, 1606, “Mastlin became

em-

broiled in a very serious and very sharp quarrel with the [other] professors, who, on the basis of arguments drawn from Holy Scripture, denied that the earth

moves. Mastlin, having found that all the movements in the heavens are more regular according to Copernicus hypotheses, is unwilling to depart from them" (Gesam. Werke, XV, 355:43-47). The foregoing account was sent to Kepler by samuel Hafenreffer, the principal participant in this disputation, over which Mästlın presided (sce fn. 385, below). Kepler, who made the first great improvement in the Copernican astronomy, gratefully acknowledged his intellectual indebtedness to Mästlin’s public lectures

at Tübingen University. Would the development of modern science have been the

Kepler's Notes on the Dream

65

The lighter the weight a man carries on his delicate bones, The swifter he flies to the heavenly homes. The

fine delicacy

of Mästlin’s mind

you who are annoyed, forgive me.

is well known.

Meanwhile,

60. Here is Aulis and the covenant which ruined Troy.'?? Yet it was my intention merely to joke and reason jocularly. If it is true, as most courts hold with regard to witches, that they are transported through the air,? I say that maybe it will be possible, also, for some body to be violently removed from the earth and carried to the moon. 61. In thinking up jokes, you should bear this, too, in mind, that while you believe you are winning the approval of one listener within the hearing of another, you deeply offend the latter and also his neighbor. Even so, Germany is just as famous for corpulence and gluttony as Spain is for genius, discernment, and temperance. Therefore in the exact sciences, the category to which astronomy belongs (especially this lunar astronomy, which stands in an unusual position if an observer looks out from the moon), should a German and a Spaniard exert themselves equally, the latter would same, or would it have been even further retarded, if Mastlin had not introduced Kepler to Copernicanism at Tübingen? 132. Aulis was the port where the Greek fleet assembled for the attack on Troy.

But adverse winds prevented the ships from sailing until the commander-in-chief agreed to sacrifice his daughter, and thereby launched the expedition which conquered Troy. This ancient tale was forcefully recalled to Kepler's mind when he

reread his statement that the Daemons mother, who was born in 1547 and was the Dream began to circulate in 1611, he VIII, 672:11). To superstitious eyes, she

preferred dried-up old women. His own therefore well over sixty years old when himself described as "small, thin" (Frisch, looked just like the kind of dried-up old

woman preferred by the Daemons, according to her own son. But when Kepler

wrote the text of the Drearn, he had no thought of witchcraft in his mind. ‘That thought arose in the minds of others after they had heard about his Dream. His

mother's

trial for witchcraft

subsequently caused

Kepler bitter anguish,

which

affected his Notes on the Dream, but not its text. Throughout his valiant fight to prove that his mother was not a witch, Kepler never expressed disbelief in witches as such. 133. The kind of court ruling which Kepler had in mind may be exemplified by 3 decision handed down at Zürich in 1520: "A witch, who used to fly on a greasy stick to Mt. Heuberg (in the southern part of the Black Forest), is condemned to be burned to death at the stake" (Joseph Hansen, Quellen und Untersuchungen zur Geschichte des Hexenwahns und der Hexenverfolgung im Mittelalter, Bonn, 1901; reprinted, Hildesheim: Olms, 1963, p. 609, No. 223). For Kepler's failure to transcend the witchcraft superstition of his time, see Edward Rosen, "Kepler and Witchcraft Trials," The Historian (1966) 28:447-50.

66

Kepler's Notes on the Dream

come out far ahead. And that is why I predicted that this book would be laughed at by the Germans, but held in some esteem by the Spaniards. 62. The duration of a central lunar eclipse from beginning to end exceeds this period by a few minutes when the luminaries are located at their apogees. For the parallax of the sun is o 59”, and of the moon, 58’ 22”; the sum is 59’ 21"; the sun's radius 1s 15^ 0”; therefore the radius of the shadow is 44^ 21". To this, add the moon's radius, 15’ 0”; the sum, 59’ 21”, is restored. But in an hour the true motion of the moon is 29' 44"; of the sun, 2^ 23"; of the moon away from the sun, 27’ 21". Double this for two hours, and subtract, leaving 4' 397,388 However, 4’ 33" 30” are completed in ten minutes, and the remaining 5” 30o' in twelve seconds.39 Therefore, the entire duration becomes 4^ 20? 255.* Yet this great length is very rare. Consequently, if a body leaving

the earth is to be transported to the moon, either it should be car-

ried around high up in the cone of the earth's shadow for many days so that it will be right there at the instant of the moon's entry

into this cone or, if this arrangement is in violent opposition to and conflict with the nature of the body, it will accomplish the entire

journey from the earth to the moon within that very short time during which the moon remains within the cone of shadow. An additional reason is furnished by the theory of magnetism. The moon is a body akin to the earth. This conclusion 1s supported by many arguments adduced by one of the interlocutors in Plutarch’s book

on The Face in the Moon,'** which is appended hereto. Aristotle 134. 2 X 27 21" = 54' 42"; 59 21" — 54° 42" = 4' 39". 135. The moon moves 27' 21" away from the sun in an hour, and therefore

4’ 33" 30"' 1n ten minutes. 136. 4' 39" — 4' 33" 30'" = 5” 30°”; 4' 33" 30” (or 273.5”) in ten minutes (or 600 seconds) equals 5” 30°” (or 5.5”) in twelve seconds. 137. The time during which the moon is completely immersed within the

earth's shadow in the course of a central eclipse is put by Kepler at 2" 10" 12°. He doubles this interval in order to obtain the entire duration of the eclipse,

from dow,

the moment of the first contact, when the moon begins to enter the shato the moment of the last contact, when the whole disk of the moon has

emerged from the shadow: 2 X 2"10™12° = 4*20"25*. This (fractionally imprecise) computation differs slightly from the 4"20"4* or 4"18"18* given by Kepler in his

Epitome (Gesam. Werke, VII, 494:21—22). 138. 934A-935C. Kepler's Note roo on his translation of Plutarch’s Moon refers to the present passage in Note 62 on the Dream, and not to Note 63 (as in Somnium, 1634 ed., p. 171, note n; repeated by Frisch, VIII, 120:19 up). Since Note

Kepler’s Notes on the Dream

67

also is drawn into this camp by his Arab interpreters.**? Unless I am mistaken, they urge upon us the passage in Book II, Chapter 12, of On tbe Heavens,'*° concerning which see the Preface to Book

IV of my Epitome of Copernican Astronomy.'*' But the clearest 62 on the Dream speaks of Plutarch's Moon

as “appended

hereto," that Note

was

written in or after 1624, when Kepler was offered the Greek text of the Moon, from which he made his Latin translation appended to the Dream (see Appendix D,

below). 139. The twelfth-century Muslim commentator Ibn Rushd (Averroes) misattributed to Aristotle the statement that "since the moon in itself is dark, and is

bright on account of another body, it is therefore similar to the earth in nature"

(in the Latin translation of Aristotle's collected works, and of Ibn Rushd's commentaries on them; Aristotelis opera cum Averrois commnentariis, Venice: Giunti, 1562-74; reprinted, Frankfurt/Main: Minerva, 1962, Vol. V, fols. 11v, 115v, 127r, 131v; Vol. VI:2, fol. 108v; Vol. IX, fol. 7v). In fact Aristotle did not re-

gard the moon as akin to the earth, or similar to it in nature. His moon is a heavenly body that moves, whereas his earth is a non-heavenly body that does not move. His moon has something in common, not with the earth, but sun “and becomes as it were a second and lesser sun” (Generation of 1V.10:777" 24-26). Nevertheless, in his Epitome Kepler falsely ascribed to the statement, "as quoted by Averroes, that the moon seems to be

with the Animals, Aristotle a sort of

etherial earth” (Gesam. Werke, VII, 319:19-21; Great Books, Vol. 16, p. 919). But the expression “etherial earth" occurs in Macrobius (Commentary on Scipio's

Dream, 1.11.17), not in Averroes, who certainly helped to make Kepler confused about Aristotle's view of the relation between the earth and the moon. For the ancient authors who called the moon the “etherial earth," see William Harris Stahl’s translation of Macrobius (New York: Columbia University Press, 1952), p- 131.

140. “The earth does not move at all, and the nearby bodies have only a few

motions" (292” 20-21). Ihe next two chapters (13-14) in Book II of Aristotle's On the Heavens were translated into German by Kepler, who added an extended commentary (Frisch, VII, 733-50). On the basis of the surviving manuscript,

Fritz Rossmann published a new edition at pp. 56-90 in his Nikolaus Kopernikus, erster Entwurf seines Weltsystems (Munich, 1948; reviewed by Edward Rosen, Ar-

chives internationales d'histoire des sciences, 1950, 3:700-703). 141. Aristotle “adduces the small number of the moon's motions as evidence of the moon's lower position and of its greater kinship with the earth" (Gesam. Werke, VII, 253:42-43; Great Books, Vol. 16, p. 848). In Aristotle's opinion, the outermost body had only one motion; the sun and moon had fewer motions than

did the planets nearer to the outermost body; this irregular increase from one to many to few (instead of from one to few to many) was mystifying. Yet, despite his puzzlement, Aristotle did not assert any kinship between the moon and the

earth. In extenuation of the misinterpretation of Aristotle by Copernicus

(Revolu-

tions, 1, 10) and Kepler, it may be said that in the Greek philosopher's astronomy, the moon was less different from the earth than were the outer planets, because

the latter had many motions and the moon had fewer motions, and fewer motions are less different from motionlessness than are many motions. Nevertheless, to keep the historical record straight, we must never forget that in Aristotle's cos-

68

Kepler’s Notes on the Dream

proof of this kinship is in the ebb and flow of the tide, concerning

which see the Introduction to my Commentaries on the Motions of mology

a moving body, no matter how

many

motions

it underwent,

was

entirely

different from, and had no kinship with, a body that never moved. Kepler was mistaken in thinking that Averroes had in mind a passage in Aristotle’s On the Heavens. Actually, the Muslim commentator was discussing the

Generation of Animals, ii.11, 761° 13-22, where Aristotle points out that living things may be assigned to earth, water, and air, as three of the four elements. But because fire, as the fourth element, lacks its own form of life, “such a type must be sought on the moon, since this seems to share in the fourth zone,” fire, in the order of increasing distance from the center of Aristotle’s universe. This statement of Aristotle’s, that the moon has a share in fire, was interpreted in his own non-Aristotelian fashion by Averroes: “Aristotle says that the moon has a closer relationship with the element earth than with the other elements. In that passage

he seems to be examining the accidental properties held in common

ments

and the heavenly

by the ele-

bodies, insofar as these are simple. For, the light of the

heavenly bodies seems to have a nature identical with that of fire as a form. This is especially true of the moon’s light. For, just as fire shines because it is a form of dense earthy body, so also the moon, on account of its density, seems to outshine all the other parts of heaven. Of the elements, one is in itself luminous and transparent, like fire, whereas a second element shines [only] because of another, like

earth and the remaining elements. The situation is the same among the heavenly bodies. For, since the moon shines because of another body, and in itself is opaque,

it is for that reason similar in nature to the earth.” This conclusion is found, not in a work of Aristotle on animals, as Averroes repeatedly insisted, but in his own commentary on Aristotle's Generation of Animals (Aristotelis opera cum Awerrois conmnentariis, Vol. VI:2, fol. 108v). For an illuminating elucidation of this passage in the Generation of Animals, see L'Antiquité classique (1949), 18:287-313, where William Lameere identifies the beings living in Aristotle's fire as daemons. This was also the opinion of Agostino Nifo, who completed his commentary on Aristotle’s Generation of Animals at Salerno on June 13, 1534 (Nifo, Expositiones in ommes Aristotelis libros de [animalibus], Venice, 1546, p. 151 of the separately paginated commentary on the Generation of Animals). In his preface, which was addressed to Pope Paul III, Nifo said:

“There are some animals which are not subject to our sense perceptions, like those at the bottom of the sea or in the depths of the earth or in the concave [sphere of

the] moon. The latter are believed by the Platonists to be daemons” (fol. , 4r). Nifo had written a separate work De demonibus, which he finished in 1492, published for the first time in 1503, and revised in 1527. In his Expositiones Nifo de-

clared: "In my judgment Averroes interprets the Generation of Animals incorrectly" (fol., 2v). But Averroes was regarded as a reliable authority on Aristotle by Copernicus, Mastlin, and Kepler. They accepted Averroes’ assertion that in a work on animals Aristotle declared the earth and moon

identical in nature, even

though they could not have found any such statement in any of Aristotle's works, and could easily have found its opposite. For an analysis of Copernicus! shortcomings in this respect, see Edward Rosen, "Copernicus Quotation from Sophocles," in Sesto Prete (ed.), Didascaliae, Studies in Honor of Ansehn M. Albareda (New York: Rosenthal, 1961), pp. 369-79.

Kepler's Notes on the Dream

69

the Planet Mars.‘ When the moon is located directly above the Atlantic Ocean, the so-called Southern Ocean, the Eastern Ocean, or the Indian Ocean, it attracts the waters clinging to the sphere of the earth. The effect of this attraction is that from all sides the 142. “If the earth ceased to attract its own waters to itself, all the water in its seas would be lifted up and would flow into the body of the moon. The sphere of the attractive power which is in the moon extends as far as the earth”; that this is

the “explanation of the ebb and flow of the tide” was emphasized

by Kepler’s

sidenote (Gesam. Werke, III, 26: 1-3). This passage in the Introduction to his New Astronomy was recalled to Kepler’s mind decades later. Plutarch's Moon (940A) mentions the theory that the flooding of the earth's waters is produced by a liquefying action of the moon. On this

popular ancient theory Kepler wrote the following footnote: “The tides ebb and

flow. 'That is a definite fact. Equally definitely, a liquefying action of the moon is not a cause of that fact. How the moon causes the ebb and flow of the tide was

first discovered by me, as far as I know, in the Introduction to my Commentaries

on the Motions of Mars. This is how it happens. The moon, not insofar as it is wet or liquefying, but insofar as it is a mass, akin to the mass of the earth, by a mag-

netic force attracts the waters, not because they are liquid, but because they themselves possess earthy substance, on account of which they share in the movements

of a heavy body" (Sormnium, 1634 ed., p. 165; Frisch, VIII, 118, Note 90). Here in Note 9o on his translation of Plutarch's Moon Kepler used the term massa (“mass”), without feeling any need to explain what it meant. From the con-

text it is clear, however, that in this passage "mass"

denotes simply "solid sub-

stance." In this sense it is quite close to the pre-Newtonian conception of "mass" as "quantity of matter," and has not yet been re-defined as inertial resistance to an

accelerative force. For Kepler's contribution to the development of the concept of inertial

mass,

University

53-58.

see

Press,

Max

1961;

Jammer,

Concepts

reprinted,

of

New

Mass

York:

(Cambridge,

Harper

Mass.:

Torchbook,

Harvard

1964),

pp.

In Note go on Plutarch's Moon Kepler claimed priority in the discovery of the way in which lunar attraction operates as a cause of the tides. However, in a letter

written early in 1607, he referred to a predecessor, “a German," whose book “con-

tains an accurate explanation of the ebb and flow of the ocean tide and of the other movements of the ocean; the name of the author is missing . . . . From that

German author the following speculation arose in my mind: the seas are attracted by the moon, as all heavy bodies and the seas themselves are attracted by the

earth. But the attraction exerted by the earth is stronger. Therefore the seas do not leave the earth and do not rise up into the air” (Gesam. Werke, XV, 387:29-

39).

Kepler's discovery of the process by which the moon's attraction helps to cause

the tides was not accepted by Galileo, who

said:

"Of all the great men who

have

speculated about this marvelous natural phenomenon, I am surprised more by Kepler than by the others. He, whose

mind

was

free and

acute, and who

had

at his

disposal the motions ascribed to the earth, nevertheless lent his ear and gave his consent to the moon's domination over the water and to occult qualities and similar childish notions" (Galileo, Opere, VII, 486:30-35; p. 462 in Drake's translation

of Galileo's Dialogue).

70

Kepler’s Notes on the Dream

waters is not But in moves

rush to the huge area which is directly below the moon and closed off by the continents, so that the shores are exposed. the meantime, while the waters are in motion, the moon away from its position directly above an ocean. The mass of

water beating against the western shore is no longer affected by the

attractive force, flows back, and in turn pounds against the eastern shore. In my Harmonics, Book IV, last chapter, I discussed an additional reason for the ebb and flow of the tide,!? a reason which is connected with this one.!** But the one I treat here is sufficient for the present purpose. For if the daemons live nowhere else ex-

cept in the cone of shadow, but are conceived as hurrying a body upward toward the apex of the cone, unless the moon is present at the same time in its passage through the cone, surely they will be alone, without any help from anything, toiling, sweating, and, naturally, exhausted. But if they undertake their work when the moon Is favorable, its presence in the shadow will aid their efforts with

the magnetic pull of a kindred body. See Note 78, below. 63. Here the shortness of the time for this trip has in fact an-

other explanation derived, not from the duration of the longest eclipse, nor from the nature of the body, but from the attitude of the travelers.

64. Ihe whole sentence belongs to the allegory. Since remark-

able and important eclipses are rare, and the opportunities for observing them are rare, the science of astronomy (one of the 143. "The animals on the earth breathe, while the fish gulp water in through their mouths, and in turn eject it through their gills. This breathing, in particular

the alternating action of the fish, is very similar to the wonderful

and flow of the ocean in conformity with the motions

twice-daily ebb

of the moon"

(Gesam.

Werke, VI, 270:16-19). The foregoing remarks are quoted from a passage in Kepler’s Harmonics, where he described the earth as a living animal whose breathing

produces the tides. For a long time he accepted another old tradition which held that the planets were moved by their souls. But in a remarkable feat of intellectual

self-development he succeeded in liberating his mind from the planetary souls (see Max Jammer, Concepts of Force, Cambridge, Mass.: Harvard University Press, 1957, p. 90; reprinted, New York: Harper Torchbook, 1962). On the other hand,

for Kepler the earth remained an animal with a soul.

144. According to Kepler, one reason for the tides was the force with which the

moon pulls the earth toward itself. The other reason was the breathing of the earth. The connection between these two reasons, in Kepler’s mind, was that “the earth adjusts its breathing, as it were, to the motion of the sun and moon,

just

as the times when the animals are asleep and awake by turns coincide with night and day” (Gesam. Werke, VI, 270:23-26).

Kepler's Notes on the Dream

71

spirits) does not usually become known through eclipses. But there

are philosophers who zealously cultivate all the philosophical sciences (namely, the family of these spirits). They lie in wait, I say,

for the time of the lunar eclipses; using these ladders, they dare to

climb to the moon, or strive to investigate the nature and motions of the heavenly bodies. Of the human race, the smallest fraction consists of philosophers; of philosophers, barely one or two exert themselves to enlarge the boundaries of astronomy.

65. Here I return to thinking about the nature of bodies, while

employing the fiction. 66. I define “gravity” as a force of mutual attraction, similar to magnetic attraction. But the power of this attraction in bodies near to each other is greater than it is in bodies far away from each other. Hence they offer stronger resistance to being separated from each other when they are still close together.!*?

67. lhe impact is not severe when the body which is being pushed yields easily. Consequently, a sphere of lead is jarred more violently than a sphere of stone because there is more weight in the

former, and therefore greater resistance. Hence, since the bodies are heavy, they will resist motion, and accordingly the impact of so swift a thrust will be forceful in the extreme. 68. Here, at least, I prescribed for the acuteness of the pain. Let somebody else look after the safety of the traveler, lest he be torn to pieces, regardless of whether he is asleep or awake.

69. In rounded objects the parts nearest to the cause of propul-

sion are affected the most, since they weight of the parts lying on them.

70. Our

bodies

are kept warm

are pressed

down

by the

by the heat of the constant

evaporation from the interior of the earth. This evaporation comes down either as rain or, at night in the absence of the sun’s warm rays, condensed as dew and frost. When the skin is deprived of this warm external vapor, it begins to grow rough. Also, when vapor emanates from the body, it loses the heat by virtue of which it had been emitted. By consolidating itself, it now turns into cold matter. Through the process of coagulation it acquires a motion toward the body which produces it. On making contact with the body, it imparts cold to it. Lastly, the air in the ether, being deprived of the 145. See Appendix H, “Kepler’s Concept of Gravity.”

72

Kepler's Notes on the Dream

sun’s rays, is cold in the absence of heat. Just as it is exceedingly

thin, so the cold which it acquires by itself has only the slightest effect so long as the air is not moved. But when motion 1s added, that very process confers upon the cold a certain power of condensation. As a result, the more violent the impact of the cold upon a body or of a flying body on the cold, the denser the cold becomes, the more penetrating in its fineness, and to that extent colder. The cold also becomes an active quality by the condensation of matter. Before this matter 1s condensed, in my view it is cold only negatively. The passage from the negative to the positive state I leave to others to explain. See the relevant speculation in my Optics, where it is carried out through a comparison of light and the color black;'*9* wherever you notice that I am in trouble, help me to dig out the causes.

71. See Note 57, above. 72. This is merely for the sake of formality. Nature fails me. I

do not know whether it is agreeable to pass over into a joke in the midst of a serious discussion. The allegory, too, is becoming chilly. 146. Here

in the Dream

Kepler

maintained,

in the spirit of Aristotelian

meta-

physics, that cold is transformed from a negative or privative state to an active quality

by

the

condensation

of matter.

In

the

Optics

(Ch.

1, Proposition

r5;

Gesam. Werke, II, 23:21-24) Kepler expounded a similar theory of light and color: “Color is potential light, light buried in the matter of a transparent body, if this is regarded as unseen. In the arrangement of matter, whether it be transparent or opaque, there are various degrees of rarity and density. In like manner the various degrees

of light, which is a solid form

of matter, produce the differences

in colors.” To this theory of light Kepler anticipated the objection that “darkness

is the absence [of light], and therefore cannot become something positive and an active quality, that is, radiant and bestowing color on walls.” To this objection

Kepler replied with the counter-argument that “cold, which is merely the absence [of heat], nevertheless becomes 24:1-4).

an active quality in matter"

(Gesam.

Werke,

Il,

In the clarifying notes which Kepler added when he was reading the proofs of

the Optics, he modified his theory so far as the deepest shade of black was concerned: “Extreme blackness is the terminus of all colors .... The blackest color is deprived of all potential light, and consists of pure material darkness” (Gesamı. Werke, II, 367:19-23).

The relation of light to the color black was discussed further by Kepler in the

Optics, Ch. ı, Proposition 37: “Light whitens the colors of things in the course of time.

For,

Proposition

according

to

Proposition

36,

light

destroys

matter.

15, the essence of color consists of matter. When

But,

according

to

this matter perishes,

the color of the objects perishes. Light whitens because (according to the same Proposition 15) white things are closer akin to light; black things partake more of

shadows and the density of matter. Therefore things" (Gesam. Werke, II, 37:7-11).

light has more

to remove

in black

Kepler’s Notes on the Dream

73

The lack of things needed for living is made good in a thoroughly inadequate way ‘47 by that daemon, who is called astronomy, using

ing 1

the

power

he

is born

with

of ardent

passion

for

speculat-

148

73. It was not possible to omit Aristotle's appropriate story about the philosophers who strove to reach Mt. Olympus in Asia for the sake of the view.!? 74. This is certainly the case when the body has been carried so far beyond the region of the earth's magnetic force that the lunar globe's magnetic force is already preponderant. 75. When the magnetic forces of earth and moon are canceled out by their opposing attractions, it 1s as though nothing pulled the

body in any direction. At that time, therefore, the body itself as a

whole propels its limbs, these being parts which are smaller than the whole body. 76. Not entirely by will.'°° Strength, too, is needed. For each body in proportion to its matter possesses a certain inertial resistance to motion. This inertia provides a state of rest for the body in any place in which it is located beyond the reach of forces of attraction. This power or inertia must be overcome by anyone who !?! is going to move that body from its place.'”” 77. When, that is to say, the region of the moon's magnetic force

is nearby

and

147. The misprint frigde Frisch (VIII, 47:6 up).

therefore in the

1634

predominant.’ Sommium

was

For,

corrected

assume to

frigide

that

by

148. Despite its impersonal character, this remark is unmistakably one of Kep-

ler's frequent references to his irrepressible flights of fancy and to his insufficient

income.

149. In the Optics Kepler declared that “it is impossible to live on certain moun-

tains unless a sponge is applied to the nostrils, as Aristotle remarks about Olympus in his Meteorology” (Gesam. Werke, II, 125:3-5). In the Epitome Kepler similarly asserted that “on Mt. Olympus in Asia, according to Aristotle, life cannot be

sustained unless the breath is drawn in through damp sponges” (Gesam. Werke, VII, 63:8-9). Whoever misled Kepler into believing that Aristotle made any such statements about a Mt. Olympus in Asia evidently provided Kepler with his device for taking care of his space traveler’s breathing. 150. See above, Dream, fn. 19. 151. The misprint quid in the 1634 Somnium was corrected to qui by Frisch

(VIII, 48:6). 152. See Appendix I, “Kepler’s Concept of Inertia.” 153. Here Kepler retreats from his approach to that aspect of the inertia principle according to which a state of motion perseveres. Instead, he falls back on his

favorite force, magnetic attraction.

74 /

Kepler s Notes on the Dream

some portion of the earth is equal to the lunar globe and exerts an equal force of attraction. A body located between the tWo globes at the point where its distance from each is in the same ratio as are

the bodies to each other will remain motionless,* since the pulls in opposite directions eliminate each other. This will happen if the body's distance from the earth is 58 1/59 earth-radii, and from the moon 58/59 earth-radii.^* But when the body moves a little

closer to the moon, it will be subject to the moon's attraction,? since the moon's force is dominant on account of its nearness.

154. Here a body is held motionless by equal and opposite gravitational attrac-

tions exerted by two other bodies. If these two bodies are equal, then the motion-

less body will be exactly halfway between them. But if the two attracting bodies are unequal, then the motionless body will be "located between the two globes at the point where its distance from each is in the same ratio as are the bodies to each other." In other words, the distances are inversely proportional to the attracting volumes. 155. In a letter to Fabricius, dated October i1, 1605, Kepler wrote: "Since the moon's body is like the earth's, I say that if motion and animate force are taken

away from both bodies, they will come together. The moon is about one-fortieth

of the earth. The distance between these celestial bodies is 6o earth-radii. This is a ratio of 41:60 or 1:1%. Therefore the place where the two bodies meet is 175 radii above the center of the earth on the way toward the moon” (Gesam. Werke, XV, 243:132-36). In the New Astronomy’s Introduction, which he may have written after the letter just cited, Kepler made the ratio between the attractions exerted by the earth and the moon about 53:1, on the assumption that the two bodies had the same density (see Appendix H, below). But here in Note 77 he altered the ratio to about 58:1. In progressively increasing the ratio of the earth’s bulk to the moon's from 40:1 to 53:1 to 58:1, Kepler swung from one side to the other of 49:1, the ratio accepted by modern astronomers, who also believe the moon's density to be only three-fifths of the earth's.

In his above-mentioned letter of October 11, 1605, Kepler attributed to both the

moon and the earth vim animalem ("animate force"; Gesam. 243:133). This "animate force," according to Kepler, counteracted between the moon and the earth: “Each is held back by its soul so not come together, just as by an animate force (that is, by gravity) I my head which, in the absence of this force, would be dragged ground by the magnet which is the earth” (Gesam. Werke, XV,

Werke, XV, the attraction that they do hold up high down to the 243:136-39).

Through a peculiarity of the Latin language Kepler's conception of this animate

force has been grossly misunderstood. From the word for "soul" (anima), Latin forms the adjective "animalis" (animate). Kepler's expression vi animali means "by an animate force," not "by an animal force." The same expression vi animali was

used by Kepler in the New Astronomy, where he took for granted that the moon and the earth

were

"kept,

each

on

its own

course, by

an animate

force

or some

other equivalent" (Gesam. Werke, III, 25:37-38; cf. 24:35). 156. In passing beyond the point of zero attraction and becoming subject to the moon's attraction, the body perseveres in its own motion (an important consideration which Kepler neglected to make explicit here in Note 77, as he did in the text of the Dream at the reference number of the Note).

Kepler's Notes on the Dream

75

78. At first it is slight, but close to the moon it is very strong,

as follows at once. Moreover, it is of little use to those who make absolutely no effort to lift the body. But to those who do try to lift the body it is helpful even when the earth is still dominant. See Note 62, above.

79. See Notes 67, 68, and 69. But let the traveler see to it that he arrives with his body so unharmed that he can also wake up. Here

the allegory furnishes an excellent remedy for those who are bound by a vow of virginity contrary to their natural impulses: intense, constant, and excited speculation.'?? 80. This, as was pointed out in Note 62, above, is “in violent opposition to and conflict with the nature" of bodies; indeed, it is impossible. 81. It is a very great pleasure for me now to find almost the same words in Plutarch.!?5

82. Because they are called spirits of darkness, as in Note 55, above. But the allegory compares the journey through the shadow to the observation of eclipses; the sun, to political business; the

dark caves time spent vations of was more derground

of the moon, to seclusion and scholastic obscurity; the in the caves, to continuous speculation based on obserthe eclipses. In Prague I had a residence in which no spot suitable for observing the sun’s diameter than the unbeer cellar.!?? From the floor of the cellar I used to aim

an astronomical tube, described in my Optics, through an open-

157. Here again Kepler is unquestionably alluding to his own personality. He might have pursued his voyage through life unharmed, had he held his speculative tendencies in check by conforming to the dominant views in astronomy and theology. But such a course of conduct, befitting a placid virgin, did not commend itself to Kepler's tumultuous nature. 158. In Plutarch's Moon (940F, 941D), voyagers disembark on legendary islands, and an interlocutor is urged not to rush ahead with a myth as though he were running

a ship aground

99:24). When

(Sommnium,

1634 ed., pp.

168,

171; Frisch,

VIII, 98:9 up,

Kepler was writing his Notes on the Dream, he was engaged in

studying Plutarch's Moon (see Appendix D, below). 159. In this cool place Kepler attempted to observe the moon too, as he recalled in a letter of March 2, 1629: "In the years 1603-1604 I tried to do this by means of a very long tube without lenses, let down into a deep cellar in the summertime" (Gesam. Werke, XVIII, 389:89-90). 160. Gesam. Werke, IT, 288-90. In the Optics, which was written before the

telescope eclipses,” an image through

became a scientific tool, Kepler called this device an “instrument for not an “astronomical tube.” It was designed, without any lenses, to cast of the sun on a screen in a darkened room by means of light admitted a narrow aperture.

76

Kepler’s Notes on the Dream

ing at the top toward the noonday sun on the days of the solstices.1* But this part of the allegory is treated more fully in the

next Note, No. 83. [83. Missing. | 84. This happens on the seventh or eighth day after an eclipse of

the moon,!€? as is indicated below.!$

85. Total eclipses occur more frequently in the case of the sun

than in the case of the moon.'*

86. This joke was set forth more clearly in Note 55, above. But

if you refer it to the allegory, you will now, in turn, call forth predictions of solar eclipses, derived from theory which is based on observation of lunar eclipses. 87. For in the Epitome of Copernican Astronomy, Book IV, I deduced a priori that the sun's radius 1s to the radius of Saturn's

sphere as this is to the radius of the sphere of the fixed stars.'^? If

161. Kepler's diebus solstitialibus 1s not restricted to the longest day, but includes also the shortest day. Thus on December 13/23, 1601, and again in the following December, Kepler used his instrument to determine the sun's diameter at the time

of the winter solstice, for the purpose of comparing this measurement with the

result which he obtained at the time of the summer solstice (Optics, Ch. 11, Problem 2; Gesam. Werke, II, 291:29-292:3). In the Optics Kepler, the Imperial Mathematician, emphasized that he made these observations in a dark room, but he did

not then reveal that this was a beer cellar. 162. A lunar eclipse can occur only when the moon is directly opposite the sun, with the opaque earth coming between the other two bodies, intercepting the light of the sun, and casting a shadow on the moon. After a short time the moon moves out of the earth's shadow and is once again fully illumined by sunlight.

About a week later, as the moon moves away from its opposition to the sun and enters its gibbous phase, a previously illumined part of its surface no longer re-

ceives any sunlight and lies in shadow. 163. This is a promise which Kepler forgot to keep. This unfulfilled promise suggests the reason why certain other scheduled sections of the Dream are missing (Notes 5 and 83 on the Dream as well as Notes 25, 27, 37, and 38 on the Geographi-

cal Appendix). 164. When the tip of the moon's shadow strikes the earth, an observer within the cone of shadow sees the sun totally eclipsed. Solar eclipses which are total somewhere or other on the earth's surface occur on the average about eighteen months apart; total lunar eclipses are slightly more frequent (71 being the average number in a century, as compared

with 66 total solar eclipses, according to Frank

Dyson and R. v. d. R. Woolley, Eclipses of tbe Sun and Moon, Oxford, 1937, p. 10, based on Oppolzer,

Canon

of Eclipses).

165. Kepler believed the sun and stars to be fixed in place, by contrast with the planets, which he called the "movable bodies." In his time the outermost known planet was Saturn, which he therefore regarded as terminating the region of the movable bodies. On the basis of a priori considerations concerning the arrange-

Kepler's Notes on the Dream

77

this 1s true, then the radius of Saturn's sphere is barely 1/2000 of the radius of the sphere of the fixed stars; !% the radius of the sphere containing the earth and the moon is hardly 1/20,000; ' and the

radius of the moon's sphere 1s 1/59 of the radius of the sphere con-

taining the earth and the moon.'® The distance from the earth to the fixed stars, therefore, varies by no more than 1/10,000; **° to

this tiny variation about 1/30 is added by the moon's variations."^ ‘Thus the entire variation of the moon from the fixed stars becomes utterly imperceptible. 88. Ihe moon always turns the same spots toward us earth-

ment and proportions of the heavenly bodies in space, he reached the following

conclusion: “The radius of the region of the movable bodies is a mean proporuonal between the radius of the sun's body and the radius of the sphere of the fixed stars. Hence, the globe of the sun stands in the same ratio to the spherical

system of all the planets as this system has to the entire universe's spherical body,

which is bounded by the region of the fixed stars” (Epitome; Gesam. Werke, VII, 285:38-41; Great Books, Vol. 16, p. 883). According to Kepler, then, the universe

is a sphere which, despite its immensity, is bounded by the stars. He explicitly rejected the thesis that the universe is infinite. To the question “whether the sphere of the fixed stars is infinite in extent," Kepler devoted a whole chapter of his New

Star, where

he concluded

that “an infinite body

cannot

be understood

even in thought" (Gesam. Werke, I, 257:11-12). 166. Attaching numerical values to his a priori mean proportional, Kepler estimated

that "the diameter of Saturn, the outermost

sphere

of the movable

bodies,

contains within itself the diameter of the sun's body approximately 2,000 times. In like manner, the diameter of the sphere of the fixed stars would contain within itself the diameter of Saturn about 2,000 times" (Gesam. Werke, VII, 286:6-8). 167. Kepler calculated that "the diameter of the earth's sphere, which is located around the sun, is a little larger than one-tenth of Saturn's sphere" (Gesam. Werke, VII, 286:1-2). Consequently he reckoned the sphere containing the earth and the moon as 1/20,000 of the sphere of the fixed stars: 1/10 X 1/2000 = 1/20,000. 168. The “moon’s sphere" means the spherical region within which the moon revolves

around

the earth.

This

“moon’s

sphere"

was

equated

bv

Kepler,

compar-

ing the lengths of the radii, with 1/59 of the "sphere containing the earth and the moon," that is, the region within which earth and moon revolve around the sun. 169. 'The greatest variation in the earth's distance from the fixed stars occurs at

two diametrically opposite points on the earth's sphere. Since this sphere's radius is 1/20,000 of the sphere 1/10,000.

of the fixed stars, the maximum

variation

is 2/20,000

170. The radius of the moon's sphere, or the distance from the moon

or

to the

earth, is 1/59 of the distance between the earth and the sun. Hence the greatest variation in the distance from the moon to the fixed stars is 2/59 or about 1/30 of the earth's maximum variation. Since this is 1/10,000 of the radius of the sphere of

the fixed stars, the moon’s greatest variation is 1/30 X 1/10,000 or 1/300,000 of its distance from the stars. The minuteness of these variations, in comparison with the enormous remoteness of the fixed stars, makes the stars look the same, whether they are viewed from the earth or from the moon.

78

Kepler’s Notes on the Dream

dwellers. Hence we know that it revolves around the earth just as

though

it were

attached

to the

earth

by

a cord,’

and

that

whereas its upper part never faces the earth, its lower part or hemi-

sphere always does so. 89, 9o. What we earth-dwellers call “Earth,” I chose to call “Volva” from the point of view of the people on the moon. For

our nocturnal luminary is called in Hebrew Lebhana, from its white color;'? in the Etruscan language, Luna (derived, I think, from the Carthaginian) ;'"® in Greek, Selene, from selas, meaning “white sheen,” !** since that is how it looks to us who live on the 171. The moon rotates on its own axis in exactly the same time as it takes to revolve around the earth. The combined result of its simultaneous rotation and

revolution

is that it (almost)

always

presents

the

same

appearance

or spots

to the

earth. Kepler, however, preferred a different explanation of the moonspots’ unchanging appearance. He compared the moon to a ball held firmly by a thong and whirled around by an athlete: the athlete sees only the side of the ball that perpetually faces him, and he never gets to see the other side of the ball. Kepler's comparison of the moon with such a ball involves granting the moon only one motion:

it revolves around

the earth, but does not rotate on

its own

teleological view of the universe, such rotation fulfills a function:

axis. In his

“The sun and

the earth rotate on their own axes . . . . The purpose of this rotation is to confer

motion on the planets located around them: on the six primary planets in the case of the sun, and on the moon in the case of the earth. On the other hand, the moon

does not rotate on the axis of its own body, as its spots prove. Why is this so? The reason is none other than that no additional planet is seen revolving around the moon. Consequently the moon has no planet on which to confer motion by

the rotation of its body. Therefore, in the case of the moon, rotation was omitted as unnecessary" (Gesam. Werke, VII, 319:30-37; Great Books, Vol. 16, 919-20). 172. The Hebrew word for the moon, like the name of the country Lebanon, is derived from a root meaning "white." For Kepler's study of Hebrew, see fn. 89, above. 173. Luna is the Latin word for the moon. What the Etruscans called the moon is not known, the decipherment of their language being still in its infancy. Deceived by the similarity between Lebana (or Levana) and Luna, Kepler suggested

by implication that the Semitic word was borrowed from the Carthaginians by the Etruscans, who in turn transmitted it to the Romans. But the few Carthaginian

and Etruscan words which passed into Latin do not include luna. This term is derived from a Latin root meaning "bright"; see Alfred Ernout and Antoine Meillet, Dictionnaire étymologique de la langue latine, 4th ed. (Paris, 1959-60), p. 373. Some bold comparative philologists seek to penetrate the fog that shrouds the

period before the earliest forms of Indo-European and Semitic speech grew apart. These

scholars

relate

the

Semitic

root

/bz,

meaning

“white,”

not

to the

Indo-

European root present In luna, but to /b, as in albus, the Latin word meaning white,” and in English “albino” and “albumen.” Comparative philology has made great progress since Kepler speculated about Levana and Luna.

174. Kepler correctly derived Selene, the Greek word for “moon,” from selas, meaning “brightness”, see Emile Boisacq, Dictionnaire étymologique de la langue grecque, 4th ed. (Heidelberg, 1950), p. 858.

Kepler's Notes on the Dream

79

earth. In like manner, the name assigned by the moon’s population to our earth, which they see instead of a moon, is properly drawn from the kind of appearance it has. This sphere in fact seems to them to be rotating constantly in the heavens around its own motionless axis.!'? They are entitled to take as proof of this rotation the variation in its spots, as will be explained below.'* On account of its revolving, therefore, let it be called “Volva”; let those who see Volva be called the “Subvolvae’” or "Subvolvans"; and

those who are deprived of the sight of Volva, the “Privolvans.” 91. We on this terrestrial globe think that the celestial poles are those two opposite points in which the earth's axis, when pro-

longed in both directions, meets the sphere of the fixed stars. For as

the first motion !'* appears to us, we see these two points as sta-

tionary. These two points are not regarded by the moon-dwellers

as the celestial poles. For to them it does not seem that the sphere

of the stars revolves around those poles in that short period of time which we measure as twenty-four of our hours. On the contrary, the axis of the lunar globe is perpendicular to the plane of the ecliptic,’’® or nearly so. When this axis is prolonged, it meets the 175. To Kepler's moon-dwellers the earth seems to rotate in one place, and not to move from one place to another; that is why he says that to them the earth's axis looks motionless.

176. See Kepler's Note

around

its axis is proved

146. For Kepler’s moon-dwellers,

by

the

variation

in its spots. On

the earth’s rotation

the

other

hand,

the

constancy of the moon's spots as seen by the earth-dwellers was taken by Kepler

in his Note 88 as proof that the moon does not rotate around its axis. If Kepler's moon did rotate, its divisor would rotate with it. But this circle that divides the lunar hemisphere visible to the earth-dwellers from the lunar hemisphere invisible

to them (before they learned how to photograph the far side of the moon) remains parallel to itself and passes through the moon's celestial poles throughout the monthly revolution of Kepler' non-rotating moon around the earth. This

constancy of the divisor he deduces, at the end of his Note or, from the constancy of the moon's spots as seen from the earth. 177. What is now called the "apparent diurnal rotation of the heavens" used to be termed the “first motion." This was defined in Kepler's Epitome as the “daily motion . . . executed by the fixed stars, planets, moon, sun, and whatever other bodies are in the sky, when they rise on one side of the horizon and set on the

opposite side... . Through

this one motion alone, if no second motion inter-

venes, every heavenly body each day can rise at one and the same point on the horizon, always climb to the same height above the visible plane of the horizon, and set again at one and the same point on the horizon" (Gesam. Werke, VII, 30:22-29).

178. As the earth revolves around the sun in the course of a year, it describes an

orbit. If the plane in which this orbit lies is extended to meet the celestial sphere, the trace of this plane on the sphere is the ecliptic. The real annual revolution of

80

Kepler's Notes on tbe Dream

sphere of the fixed stars in points which are near the poles of the ecliptic. These poles are the celestial poles for the moon-dwellers, because in the period of time which we call a month the sphere of the fixed stars appears to them to rotate on this axis. The reason for this appearance is that, in fact, the lunar globe itself swings on its own axis and the two end points of that axis as though they were stationary in space. True, the lunar globe and also this axis within It revolve around the terrestrial globe in the period of a month. Nevertheless, the axis meanwhile remains parallel to itself in every position. Therefore in one revolution it is always directed toward nearly the same points on the sphere of the fixed stars, because the magnitude of the moon's orbit is imperceptible in comparison with the sphere of the fixed stars. However, the divisor circle passes through these poles of the lunar globe, as is apparent from the fact that the same spots on the moon are turned toward the earth throughout the entire time of the monthly revolution. For to the extent that we thus see the lunar globe as motionless, to that same extent does it in fact revolve around the aforementioned points.

92. The lunar globe revolves around the earth in such a way

that it always turns the same hemisphere to the earth. This hemisphere may be called the front of this globe. When the moon 1s between the sun and the earth, and appears to us as a new moon or a thin crescent, obviously it then turns its back to the sun, and its front away from the sun. But when the moon is full for us, that is to say, when we are interposed between it and the sun, it turns its back to the fixed stars and away from the sun, and presents its front to both the sun and the earth. But the sun is regarded as producing, in the entire universe, day by its presence and night by its absence. Therefore both the back and the front of the moon have their own day and night. But their dav-plus-night is not as short as the earth around the sun, and the apparent annual revolution of the sun around the earth, both lie in the plane of the ecliptic. In his Epitome Kepler defined the

ecliptic as the “intersection of the concave sphere of the fixed stars with the plane which passes through the center of the sun and the center of the earth in every position of those centers" (Gesam. Werke, VII, 112:5-6). In the course of the sun’s apparent annual revolution around the earth, twice a

vear it reaches its greatest distance Through

above

these two points of maximum

or below the plane

of the equator.

declination, a great circle may

be drawn

from the (earth’s) celestial poles. That circle is perpendicular to the plane of the

equator, and is called the “solstitial colure.”

Kepler’s Notes on the Dream

81

ours. For our entire length of a single day 93. Our days and in length because our

monthly period is used up by them for the and night. nights, apart from the equinoctial days, vary celestial poles seem to be far away from the

moon-dwellers.

the

poles of the ecliptic. But our celestial poles are not those of the On

contrary,

they

have

different

celestial

poles, which are near the poles of the ecliptic. If the tiny distance between the moon's celestial poles and the poles of the ecliptic

gives rise to any variation of day and night, that variation is not to

be compared with ours, and it is certainly not perceptible to the same

extent.

Consequently

the

moon-dwellers

have

an

almost

perpetual equinox throughout their entire globe, just as among us on the earth day and night are equal over the whole earth on an equinoctial day.

94. In my Epbemerides ? the phase of half-moon differs from

the quadrature of moon and sun !*? at the most by an interval of two of our hours plus ten minutes.!?! This difference occurs because the ratio of the lunar orbit to the path of the sun (or of the

earth)

is 1:59, at apogee,

that ıs.'”” Day

begins

for the mid-

Subvolvans,!#® however, not when the center of the lunar globe is in quadrature with the sun, but when the position of the lunar globe is put in the moon’s circle of illumination,^* which forms 179. Kepler published his Epbemerides

(Pt. D, covering the years

installment

(Pts. II-III)

was

in two installments. The

first installment

1617-20, was issued at Linz in 1617-19. The issued at Zagan in 1630; it covers the years

second

1621-36,

so that the entire work embraces the two decades from 1617 to 1636. The reprint-

ing of the Ephemerides in Frisch, VII, 479-666, is incomplete, and in Gesam. Werke the Ephemerides is scheduled to form part of Vol. XI. 180. The moon and sun are said to be in quadrature when the lines drawn to

them from the earth form a right angle.

181. In his Ephemerides (p. 27:13-11 up) Kepler said: “The phase of halfmoon, that is, the first quarter, occurs about four hours before the quadrature of sun and moon; the other half-moon, or last quarter, occurs about four hours after the quadrature of sun and moon; this is the result if I use 30:1 as the ratio of the solar and lunar orbits" (Frisch, VII, 496:24-21 up). 182. In his Ephemerides Kepler made the ratio 1:30, and the time difference between half-moon and quadrature four hours.

183. bisects 184. sun at

The term "mid-Subvolvan" is used by Kepler to denote the line which the Subvolva longitudinally. "A little more than a hemisphere of the moon's body is illuminated by the any moment. The illumination is bounded by a circle which, for this reason,

is called

the

‘circle

of

illumination’”

(Kepler,

Epitome;

Gesam.

Werke,

VII,

471:29-31). Nowadays, the line which separates the dark portion of the moon's disk from the illuminated portion is called the "terminator."

82

Kepler's Notes on the Dream

the phase. In both phases the moon comes nearer to the sun than the earth does. Therefore, that part of the moon’s orbit which is drawn between these limits on the outside around the earth 1s longer than the part which continues on the inside between the earth and the sun. And that outside part measures the day for the mid-Subvolvans, but the night for the mid-Privolvans. Consequently, the Subvolvan day and the Privolvan night add about four of our hours to the half-month, as determined by us; the same amount of time, on the other hand, is subtracted from the Subvolvan night and the Privolvan day. Furthermore, what was said about the hemispheres’ mid-regions applies also to their eastern or

western neighbors. There is only one difference:

however many

degrees of longitude separate any place from the middle, the lunar globe extends by an equal amount beyond the position in which day began for the mid-region.

95. Just as must happen on the globe of the earth at the pole on

an equinoctial day.

96. Here is the thesis of the whole Dream; that 1s, an argument

in favor of the motion of the earth or rather a refutation of the argument, based on sense perception, against the motion of the earth.

97. If "day" is defined as the sun's presence, surely the sun 1s

present wherever any place 1s seen to be illumined by its light. Unquestionably the same spots on the moon in the middle of its body are seen by us to be illumined continuously for fifteen whole days without any night intervening. For when the moon is full, if we stay in one place, we have a clear view of these spots for over sixteen hours. Furthermore, when the moon dips below the horizon for us, it is visible to others on account of the roundness of the earth. Therefore a lunar day is as long as fifteen, and as a result a lunar night is as long as more than fourteen, of our days-plusnights.**

98. We on earth—not people in general, but astronomers— reckon 99 months in 8 years, or 235 months in 19 years.?? Yet the

185. As Kepler pointed out in the Epitome, the word “day” has two meanings.

If contrasted with "night," “day” refers to “the time when the center of the sun is above the horizon." But one day, in this sense, plus one night, makes a "day" in a different sense, for which Kepler preferred to use the composite Greek word nuchthemeron (night-plus-day; Gesam. Werke, VII, 179:7-10).

186. Ihe approximate equality of 235 months with 19 years is the basis for establishing the date of Faster.

Kepler’s Notes on the Dream

83

natural lunations * are not as intimately '#® connected with our affairs as are the days and nights. Then what else can we think

about the moon-dwellers whom we imagine, if there are any crea-

tures up there capable of counting, than that they adopt those same numbers, since they have no other day? '# But for them the indi-

cation that the period of nineteen years has ended is the rising of

the same stars in precisely 1° the previous arrangement. 99. “Midvolvans” is to be understood as a term like our “meridians." But we have very many meridians, whereas their Midvolvan

Is unique because it passes through only two points exactly oppo-

site each other on the hemispheres named after Volva. Nor do these Midvolvans take the place of our meridians. For the moondwellers have their own meridians, which are in like manner drawn through the poles and the zenith of their places and which are, so

to speak, partners of the central Midvolvan. Whereas our terres-

trial meridians have no natural place of origin, their meridians do,

namely, the central Midvolvan. The sun and Volva impinge on it at the same instant, whereas they impinge on all the other meridians not at the same moment, but at different moments.

100. Since the moon is a sphere, all heavy lunar objects will tend

toward its center. Dodies will press on the surface of the sphere at right angles,’ and will regard as their own zenith that point among the fixed stars which is met by a straight line coming from

the center of the lunar globe and prolonged through their foot-

steps. Whatever stars are not at that point will be considered as being at a distance from the zenith of an observer stationed on the moon. Consequently, this is the basis for imagining an equator half187. In the Epitome Kepler explained that the term “lunation” is a synonym for “synodic month” (as distinguished from “sidereal month,” the time it takes the

moon,

as seen from

the earth, to revolve

from

any

star back

again

to the same

star). On the other hand, the synodic month is the time that elapses between two

successive new moons; “it is also called a ‘lunation,’ because within this interval the

moon’s sphere is steadily filled with light, and in turn emptied”

(Gesam.

Werke,

VII, 448:26-27). 188. Kepler is emphasizing here that the lunation or synodic month, even though it plays only a minor part in human affairs, is nevertheless measured care-

fully by astronomers. 189. This question mark was omitted by an oversight in the 1634 Sommium, and was correctly supplied by Frisch (VIII, 50:10). 190. In this sentence Kepler playfully uses the word exactae in two different senses: (a) completion of a period; (b) exactly. 191. To the straight lines tangent to the sphere at the points where the bodies meet the sphere's surface.

84

Kepler's Notes on the Dream

way between the poles, and the sun's deviation from the zenith of the places. The sun passes through the zenith of those who live at the equator, it is assumed, not every day throughout the entire year, but only on an equinoctial day. Therefore the axis on which the lunar globe revolves is not parallel to the axis of the

ecliptic, but is inclined at an angle to it. In other words, since the moon's axis is always perpendicular to the plane of the orbit through which the moon is passing at any given time, the moon's orbit is inclined to the plane of the ecliptic, and the moon's

also, is inclined to the axis of the ecliptic.

axis,

ror. The lunar nodes !?? revolve in nineteen years with a retro-

grade motion opposite to the sun's.?* In the same time, therefore,

the limits ?5 revolve, and also the poles of the lunar orbit, which

serve as celestial poles for the moon-dwellers, in a small circle 5? in

diameter. Hence in nineteen sidereal years,’°® among them twenty tropical years !?" are completed. Consequently, in nine and a half

sidereal years, that is, in ten tropical

years, the tenth

summer

occurs, with the sun in the constellation of the Goat, for those whose first summer occurred with the sun in the constellation of

the Crab. A similar thing happens to us also on the earth, but much

more slowly. For two thousand years ago our summer came when the sun was in the constellation of the Crab, and Sirius rose with the sun. Today our summer has shifted into the constellation of the Twins, although the zodiacal sign retains the ancient name of the Crab. 192. On

an equinoctial

day the sun is at the equatorial

zenith

at noon;

at that

time on all other days the sun is near the equatorial zenith. 193. In the Epitome Kepler defined the nodes of any orbit as the “two points on the ecliptic where it is intersected by the extended plane of the orbit” (Gesanı.

Werke, VII, 394:32-33). 194. A westward motion was called “retrograde” because most of the apparent motions in the heavens, like the sun’s orbital motion, are directed eastward. 19s. See fn. 111, above.

196. A "sidereal vear" is the time it takes the sun to move in its apparent annual

circuit of the heavens from a given fixed star eastward on the ecliptic back again to the same star. 197. A “tropical vear” is the time it takes the sun to move in its apparent annual circuit of the heavens from a given vernal equinox eastward on the ecliptic to the next vernal equinox. “The sun advances eastward among the fixed stars, whereas the equinoctial and tropical [or solstitial] points move westward among the fixed

stars to meet the sun as it approaches them. Therefore

the sun returns to the

solstitial points before it returns to the fixed stars where the solstitial points were at the beginning of the vear. Therefore the tropical vear becomes shorter than the

sidereal vear" (Kepler, Epitome; Gesam. Werke, VIT, 525:21-24).

Kepler's Notes on the Dream

85

102. Of these six days, only one or two are truly summer days. The others to either side diminish toward the length of an equinoctial day.

103. For I hardly dare to apply the term “temperate” to them,

too. On the moon there is no moderation, as will be made clear.!??

104. [hey have the zodiac in common with us. For our zodiac is

described by the annual revolution of the earth around the sun. But the moon revolves around our earth, just as we live all around it.

Therefore both populations have the same reason for imagining the zodiac.

105. lhese remarks are related to what was said in Note

ror.

For it stands to reason that the regard for the tropical year, if not as great as among us, is at any rate greater among the moondwellers out of respect for their own tropical year. But here take a look at the thesis of this book, and learn that what are for us among the main features of the entire universe: the twelve celestial signs, solstices, equinoxes, tropical years, sidereal years, equator, colures, tropics, arctic circles, and celestial poles, are all restricted to the very tiny terrestrial globe, and exist only in the imagination of the earth-dwellers. Hence, if we transfer the imagination to another sphere, everything must be understood in an altered form. 106. Because the moon's sphere, or its greatest distance from the

earth, 1s 1/59 of the distance between the sun and the earth. Therefore, when

the Privolvans

have

the sun on their meridian,

they

come closer to the sun than the earth does, by 1/59 of the entire

distance from the sun to the earth. On the other hand, when the Subvolvans have the sun on their meridian, they become farther away from the sun than the earth is. For when the moon is full, it Is at a distance of sixty units from the sun; the earth, fifty-nine; and the new moon, fifty-eight. But as the distance decreases, the sun looks bigger. When the moon is in quadrature, however, it and the earth are equidistant from the sun. And when it is in quadrature, as we said,!® the sun rises or sets for the mid-Privolvans as well as for the mid-Subvolvans.

107. The moon deviates from the ecliptic about 5? to either side,

as seen from the earth, but as seen from 198. In Kepler's Notes 207-17. 199. In the Drean:, p. 18, above.

the sun about the same

86

Kepler’s Notes on the Dream

number of minutes, because the ratio of the orbits is a little more than 60:1. 108. When the Privolvans see the sun on their meridian, they are closer to the sun than the earth is. When the Subvolvans see the sun on their meridian, they are farther away from the sun than the earth is. In both cases the difference is a little more than 1/60. Therefore the Subvolvans are farther away than the Privolvans by

about 1/30 of the entire distance. Hence, if the sun deviates for the Privolvans at the most by 5’ 30'"7,9? it will deviate for the Subvolvans by 5’ 20".?! These statements are made, not as though this difference were large and noteworthy, since it 1s almost

impossible for us on earth to observe one-sixth of a minute, but to remove the suspicion of any greater difference arising from this motion of the moon in latitude. If I retained that ratio of the orbits which 1s handed down by Ptolemy together with the other ancient

writers, this deviation would increase to ı5’.°°? 109. The earth and the moon revolve around

the sun in an

annual motion, with the moon also revolving around the earth at the same time. Hence it happens that when the moon comes between the sun and the earth in the phase regarded by us as the new moon, it 1s traveling in the direction opposite to the earth’s. Yet °°” it does not move as much in that direction as the earth in the other.

For the earth traverses 1/365 of its orbit daily, but the moon only 1/30 of its orbit. This lunar orbit ??* is a little bigger than 1/60 of the earth's orbit. Of this 1/60, 1/30 1s about 1/1800 of the entire path of the earth, and thus it is 1/5 of 1/365. Hence when the

moon is thought by us to be full, it traverses 6/5 as much as the earth; but at new moon, of the former. But the was written before the tion. At that time I still

4/5; and so the latter motion is two-thirds reader should be reminded that the Dreazz ratio of the orbits attained its final perfecagreed with the ancients that the sun's dis-

200. In his Note 107 Kepler put this deviation at about 5’.

201. 5’ 30" X 1/30 = 10"; 5’ 30" — 10" = 5' 20”. 202. As Kepler explains in his Note 109, he tripled the ancient orbital ratio of 20:1 to 60:1. Hence his deviation of 5’ would be 15’ on the basis of the ancient ratio.

203. The misprint ramen in the 1634 Sommium was corrected to tazen by Frisch

(VIII, 51:21). 204. The misprint

quia

in the

1634

Somnium

was

changed

by

Frisch

(VIII,

51:23) to quae. But what is needed is qui, because this relative pronoun refers back to orbis. Kepler's reasoning is as follows: Luna tricesimam tantum sui [orbis], qui cum sit....

Kepler's Notes on the Dream

87

tance is about 1,200 earth-radii, and the moon’s 60,°° so that the ratio of the orbits was not 60:1, but 20:1. Consequently, since the moon’s orbit is thus assumed to be 1/20 of the earth’s orbit, therefore 1/30 of this 1/20, that is, the moon’s daily motion, is 1/600 of the earth’s orbit, and so more than half the earth’s daily motion. Then the daily forward motion of the earth with reference to the fixed stars leaves a remainder, in the case of the new moon, of less than half, which is almost nothing. But the full moon accumulates more than one and a half. That is to say, the moon when full would advance more than four times as swiftly as when new. However, the moon is deemed by its own inhabitants to be station-

ary. Therefore the sun for its part will seem to undergo this motion

and this variable velocity in its forward

movement.

This conclu-

sion will be appealed to in Note 152, below.

110. In itself the sun does not move at all. The daily motion of

the earth on the “great circle” ?9 is attributed to the sun by the

earth-dwellers in a simple way, just as the moon-dwellers attribute to the sun the moon’s motion, which is compounded out of the earth’s annual motion and the moon’s monthly motion, and which is directed around the sun. In a more complicated way these same motions are attributed to Mercury, Venus, and Mars, whose own

apparent motions are, of course, reversed. For if the annual motion

of the earth and moon, as well as the monthly motion of the moon, ceased altogether, these planets would, nevertheless, be seen to be

moving. Mars would be observed traversing the entire zodiac, very

slowly when on the same side as the sun, but very swiftly when on the opposite side. Venus and Mercury would appear, however, not 205. According to Prolemy, the sun’s distance from the earth was

1210 earth-

radii, and the moon's mean distance from the earth was 59 earth-radii (Syntaxis, Bk. 5, Ch. 15; ed. J. L. Heiberg, Leipzig, 1898-1903, I, 425:17-20; Great Books, Vol. 16,

p. 175). Ptolemy's numerical results were rounded off by Kepler as 1200 and 6o, giving a ratio of 20:1. Whereas 6o is still retained by modern astronomy as approximately correct for the moon,

the sun's distance

from

the earth

is vastly

greater

to Kepler's

moon-

than Kepler realized, so that his improved ratio of 60:1 is now put at nearly 40o: 1. Hence

the sun's apparent

motion

would

look

far less jumpy

dwellers than Kepler imagined. 206. "In Copernicus’ astronomy what is the ‘great circle’? This 1s what Coperni-

cus calls the earth's true orbit around the sun. This orbit is located in the space between Mars’ orbit outside it and Venus’ orbit inside it. He calls it ‘great,’ not on

account of its size, since the circular orbits of the outer planets are much larger, but on account of its extraordinary usefulness in explaining the apparent motions

not only of the sun but also of all the primary planets" Werke, VII, 403:4-9).

(Kepler, Epitome;

Gesam.

88

Kepler’s Notes

on the Dream

everywhere in the zodiac, but in the vicinity of the sun, moving back and forth, sometimes a certain number of degrees in front of the sun and sometimes behind it. These appearances of their own are mingled with the motions in which the earth and moon travel, as things look to the earth-dwellers and the moon-dwellers. 111. If the motions with which the moon moves are attributed to the other heavenly bodies because visual appearances are deceiving, surely among the motions of the moon there is also the one

which makes the moon slow at apogee and fast at perigee. But it happens that the moon is very slow when full, new, halved, and in every phase in succession. When the moon is full, however, the mid-Subvolvans believe that the hour is noon, and when the moon Is new, midnight. The opposite holds for Privolva.

112. That is how long it takes the apogee to move through the

zodiac.??"

113. Assume

that the straight

line TR ?9? passes through C, the

center of the earth, and is perpen-

dicular to the line connecting C and S, the centers of the sun and the earth. TR divides the moon's Orbit into arcs, for instance, the Privolvan day TNR and night TPR. The moon's greatest inequality in the quadratures T and R is, of course, 775?,?? of which

the double is 15°. Therefore the arc which

has the

apogee

at its

the remaining

arc is

midpoint 1s traversed in 195? of time, while

traversed in 165° of time.?'? This

round.?"!

However,

they have

is the same as saying that our night is thirteen hours long, and our day eleven, or the other way a different number of hours.

207. As the moon revolves around the earth, its distance from the earth varies. The point on its orbit where it is at its greatest distance from the earth is called

the “apogee.”

This

“moves

eastward

Epitome;

Gesam.

Werke,

with

a uniform

motion,

and

same point in longitude on the zodiac in 8 Egyptian years, 311 (Kepler,

VII,

446:5-8).

The

length

returns

of

to the

days, 6 hours" this

cycle

is

Kepler s Notes on the Dream 114. Ihe

retardation

89

is due to the fact that the moon

is at

apogee; and the mid-Privolvans have their midnight at the time when we earth-dwellers see the moon full. Therefore, if full moon and apogee coincide, the Privolvan night is cumulatively long. But if new moon occurs at apogee, the Privolvan days are more nearly equal to their nights, since the opposing causes cancel each other out.?!?

115. If you assume that living creatures inhabit the moon, you

will admit that, to preserve and sustain them, there are also evaporations from the body of the moon. But a thin vapor, when surrounded by cold, is compressed into a snowy powder. This is the structure of frost. 116. In a dream it is necessary to have the freedom sometimes to invent even that which was never perceived. Thus, here the existence of winds must be assumed ?? because the spheres encounter

the ethereal air. I did not reject this cause, I recall, when I discussed

given as "a little less than nine years" in Kepler's text at this point, which fulfills his promise earlier in the text that "what varies in a period of eight vears will be mentioned later on." 208. The figure is reproduced from the Sommium, 1634 ed., p. 51. This figure and

the letters in Kepler's Note 113, and in subsequent Notes which refer to the fig-

ure, are omitted in Frisch, VIII. 209. Two of the irregularities in the moon’s motion combined to reach a maximum of 7° 30’ when the moon was in the quadratures (Kepler, Epitome; Gesam. Werke, VII, 460:16-18). 210. 180? + 15? = 195°; 180° — 15? = 165°. In the Epitome Kepler explains that the 360 parts of a circle, while usually called "degrees" (gradus), "in the case of the equator are called ‘times’ (tezpora), because it is the measure of time” (Gesam. Werke, VII, 124:4).

211. By a “natural day” Kepler meant “day-plus-night” (see above, fn. 185). "To

what do vou give the name 'circles of the natural davs, and how manv are there? One hundred and eightv circles parallel to the equator. Of these, the farthest

away from the equator are the two tropics. The others are drawn in pairs through degrees of the ecliptic which serve as delimitations equidistant from the solstices" (Kepler, Epitome; Gesam.

Werke, VIT,

186:30-33). The

greater the distance from

the equator to a “circle of the natural day,” the greater the disparity between the lengths of the day and night in that “natural day.”

212. In the Dream (p. 17, above) Kepler asserted that the Privolvan night is longer than its dav. When the moon is at apogee, the diurnal motion seems slower

to Kepler’s moon-dwellers. Hence, if the Privolvans’ night occurs when the moon is at apogee, the disparity between their night and dav increases. But if the

Privolvans’ day occurs when

night out.

and

day

diminishes,

the moon

because

these

is at apogee, the disparitv between their two

opposing

causes

cancel

213. Kepler assumed the existence of air and water on the moon.

each

other

90

Kepler's Notes on tbe Dream

the reasons why the time of morning is more pleasant and more

healthful for everything that lives and grows on the earth,*** and also why snow lasts on the tops of most mountains,?? even in the tropical zone.

117. I equate the Privolvan day with only fourteen of our days, but their night with fifteen of our days. The reason is that the lines SL ?!* and SV, which are drawn from S, the center of the sun, tangent to the moon's orbit at L and V, divide LPV, the outer part

of the orbit, from LNV, the inner part, and make the outer part longer than the inner part by about 4?, according to the scale of the proportion of the orbits. But the mid-Privolvans are in the shadow of the moon throughout the entire outer arc; at L and V, the two

points of the tangency, they are illumined by the sun's first and last

rays; and they receive the rays throughout terior arc LNV.

the orbit's entire in-

118. From the earth we see the sun 30’ in size. When the moon

Is new, it comes about 1/59, or a little less than that, closer to the sun than we and our earth do. Therefore, in that lunar hemisphere which is then illumined by the sun, the latter looks bigger by a tiny bit, that is, by about half a minute.?'" The ancients, however, believed the ratio of the orbits to be much smaller, namely, 1:18,??? which would make the sun look a little less than 2^ bigger.??

119. As in Note 109, above. For to the mid-Privolvans the sun

214. In his New Star Kepler raised the question “whether the time of morning is

more pleasant because the parts of the earth on which the sun is rising are at that moment carried directly into the ethereal air, whereas the parts where the sun is

setting are then, as it were, snatched away from the ethereal air" (Gesam. Werke, I, 233:15-18). A preference for the morning as the best time of the day was attributed to Pythagoras in Diogenes Laertius (Lives, viii.26). 215. “It stands to reason that most mountain

biography

of

that

elusive

peaks which are covered

thinker

with per-

petual snow or ice are higher during the greater part of the year than the surface of the air" and therefore protrude into the ethereal air (Kepler, Epitome; Werke, VII, 63:2-3).

216. See the figure on p. 88. The letters in Kepler's Note

Gesam.

117 were altered bv

Frisch in order to accommodate them to his Fig. 1 (Frisch, VIII, 56). 217. 30' X 1/59 = 1/2’. 218. Aristarchus, On the Sizes and Distances of tbe Sun and Moon, Proposition 7: "The distance of the sun from the earth is greater than 18 times, but less than 20 times, the distance of the moon from the earth” (Thomas Heath, Aristarchus of Samos, Oxford, 1913, p. 377; reissued, 1959). In his Note 109 Kepler rounded this ratio off as 1:20. 219. 30' X 1/18 = 1%".

Kepler's Notes on the Dream seems to move

one-third more slowly at their noon

91 than it does to

the Subvolvans at their noon.??? 120. On the assumptions which we made in Note 116. Of course, when the moon is new, it is rubbed against the ethereal air one-fifth more gently than the earth is, and one-third more gently

than when it is full.??!

121. Almost twice, I say. The sun's greatest distance from the earth 1s 101,800; when Mars comes closest to the earth, Mars’ dis-

tance from the sun is 138,243.?? Therefore, if the earth at its greatest distance from the sun had the same longitude as Mars at its nearest approach

to the sun, the distance between

the earth and

Mars would be the remainder 36,443.22? Now, in accordance with the opinion of the ancients, assume the moon's orbit to be simply

1/18 of the sun's orbit in a comparison of their diameters, and also assume the moon to be full so that the Privolvans at their own mid-

night have Mars at its closest approach. The amount by which they

220. In his Note 109 Kepler reasoned that the motion of the new moon (at midPrivolvan noon) is two-thirds of the full moon's motion (at mid-Subvolvan noon). Hence at noon the sun's apparent motion would seem one-third slower to the Privolvans than to the Subvolvans. This comparison concerns the moon's motion considered by itself. This motion was estimated by Kepler in Note rog as more than one-half the earth's motion. Hence, the combined motion of moon and earth is less than one-half the earth's motion when the moon is new and traveling in the direction opposite to the earth's. But when the moon is full and traveling in the same direction as the earth, the combined motion exceeds 3/2 the earth's motion. Thus the full moon travels four times as fast as the new moon. 221. In his Note 109 Kepler reasoned that in its daily motion the new moon traversed four-fifths as much as the earth, or one-fifth less, and two-thirds as much as the full moon, or one-third less.

222. In order to have a convenient way of expressing the relative distances of

the planets, a numerical value of 100,000 was arbitrarily assigned to what is now called the “astronomical unit"—the mean distance between the sun and the earth. On this basis the earth’s aphelian distance—its greatest distance from the sun—is given here as 101,800; and Mars' perihelian distance—its least distance from the sun—is given here as 138,243. These numbers are identical with 1,018 and 1,382 in

the table of planetary distances which Kepler drew up on a basis of 1000 (instead of 100,000) and which he published in 1619 in his Harmonics, Bk. 5, Ch. 4. These planetary distances, Kepler explained, were derived from Tycho Brahe's observa-

tions (Gesam. Werke, VI, 308:37-39, 309:12, 15; Great Books, Vol. 16, pp. 102526). Nearly a quarter-century earlier, in his Cosmographic Mystery, Kepler gave

the

earth's

aphelian

distance

as

1,042,

and

Mars’

perihelian

(Gesam. Werke, I, 74:33-34). But these numbers were by Kepler before he had access to Brahe's observations. 223. 138,243 — 101,800 — 36,443.

derived

distance

as

1,393

from Copernicus

92

Kepler's Notes on tbe Dream

would

come

closer

to

Mars

than

we

earth-dwellers

is

1/18 X

101,800 = 5,655. But the ratio of this number to 36,443 1s even

smaller than one-sixth.?* Therefore the Subvolvans at our new moon, which is their full Volva, would see Mars less than one-third smaller ?9 than would the Privolvans at our full moon, which 1s their midnight. Hence, with the more accurate ratio of the orbits, which I used

in the Rudolphine

Tables,?* this proportion is diminished. As a

result, the moon’s approach to Mars is not as much as 1/21 part of the sun’s distance from the earth, and therefore the difference of the appearances among the Privolvans and Subvolvans is a little less than 1/11 of this whole distance. 122. The elongations of Venus and Mercury from the sun can be observed also by the mid-Subvolvans, but under those circumstances the moon's distance from the sun does not differ much from the earth's. To those who live on the divisor, however, the

sun appears on the horizon when the moon is either full and at its greatest distance from the sun or new and at its closest approach to the sun. The elongations of these planets are, of course, observed

immediately before the rising or after the setting of the sun, especially in the case of Mercury. According to the true ratio of the

Orbits, the variation in the rectilinear distance between the sun and 224. Hence the Privolvans at their midnight would

see Mars less than one-sixth

larger than it would appear to us earth-dwellers. But “less than one-sixth larger" is a long way

from

“almost twice." This latter ratio, which

Kepler

put in the text

and repeated here in his Note 121, would be correct onlv if the moon's orbit were

one-sixth of the earth's, instead of one-eighteenth. 225. By a slip of the pen Kepler wrote triplo minorem ("three times smaller"), where he undoubtedly meant tertia parte minorem (“smaller by one-third"). The Subvolvans at new moon are 1/6+ 1/6 — 1/3 farther away from Mars than the Privolvans at full moon, and would therefore see Mars one-third smaller, not three

times smaller or one-third as large. For a recent analysis of careless computational errors in the last two chapters of Kepler's New Astronomy, see Otto Neugebauer,

"Notes on Kepler," Communications on Pure and Applied Mathematics (1961), 14:593-97. A similar conclusion was reached by Owen Gingerich, “The Computer versus Kepler," American Scientist (1964), 52:218-26.

226. Kepler named his Rudolphine Tables in honor of the Holy Roman Emperor, Rudolph II, who appointed him in 1601 to be Imperial Mathematician. From that time on Kepler worked intermittently at the Tables. Although they were not finally printed until 1627, they were completely ready for the press in 1624. Hence Kepler's reference here in Note 121 to the decrease in the ratio of the moon’s orbit to the earth's was based on the Rudolphine prior to their publication.

Tables in their manuscript

form

Kepler's Notes on the Dream

93

the moon is about 1/30 of the total,??” and therefore the variation in these elongations is not much different.

123. For Venus to look bigger to the moon-dwellers than to the

earth-dwellers, there must be the closest approach of Venus to the earth, and of the moon to the sun. However, when the moon is at its closest approach to the sun at our new moon, the midSubvolvans see neither the sun nor Venus, since they then have their midnight. Hence this sight is left for those who live on the divisor. The variation in the appearance of Venus among the Subvolvans is, however, a little more obvious than is the variation

in the appearance of Mars among the Privolvans (although these inhabitants of the divisor can obtain a view of both planets). 'The reason is that when Venus and the earth come closest to each other,

the distance smaller than

between them is 25,300.79 Since this number is 36,443, given above??? for the distance between

Mars and the earth, a larger ??? part of it 1s taken up by the diameter of the moon's orbit.

124. Ihe divisor circle is defined above ??! as passing through the poles of the moon's monthly revolution. But the lunar orbit has

a latitudinal element, to the north in one region, and to the south in the other region. The moon's axis, whose end points are these

227. By “the true ratio of the orbits” Kepler means, as he explained in Note 109, that the moon's orbit is 1/60 of the earth’s orbit. Hence the difference between the greatest and least distances from the sun to the moon is 2/60 or 1/30. 228. In the Harmonics (Gesam. Werke, VI, 309:16, 19; Great Books, Vol. 16, p.

1026) Kepler put the earth's perihelian distance at 982, and Venus' aphelian dis-

tance at 729. Hence the distance between Venus proach to each other would be 253. 229. See Kepler's Note 121.

and the earth at their closest ap-

230. The moon's distance from the earth is a larger part of Venus’ perigee dis-

tance (25,300) than it is of Mars' perigee distance (36,443). As we saw in fn. 168, above, Kepler equated the distance moon-earth with 1/59 of the distance sunearth: 1/59 X 100,000 = 1695 = 1/15 X 25,300. On the other hand, 36,443 + 1695 = 1/20.

The distance moon-earth would have to be half of Venus' perigee distance to

justify Kepler's statement in the text that Venus

the moon

sometimes

looks twice

as big to

as it does to the earth. Yet even in his youth he put Venus' perigee

distance at 217 (958 — 741), and the distance earth-moon at 6o (Gesam. Werke, I, 74:34-36, 75:1). But 6o is far less than half of 217. Nevertheless, in his characteristic way, Kepler let the original statement remain in the text unaltered when he

was preparing the Dream for publication decades later and accepted a ratio even further removed from one-half. 231. In the Dream (p. 17, above) and in Kepler's Note 91.

94

Kepler's Notes on tbe Dream

poles, is assumed to meet the plane of the eccentric orbit **? at right angles. Therefore neither of the moon's poles comes closer to the sun than does the other pole. Nevertheless, it happens that the pole of our ecliptic, which is regarded by them as the mean ecliptic, is different from the pole of the moon's orbit, since the lunar pole

revolves around the earth's pole in a period Hence, when

the position of Venus

of nineteen vears.

1s sought between

the earth

and the sun, it must be observed then not through its elongation in longitude,

but only through

its latitude.

However,

its southern-

most point is in the sign of the Fishes, and its greatest distance from the sun not much farther ahead, at the beginning of the Water Bearer. Yet at that time it is seen from the earth and the moon in the opposite signs, the Lion and the Virgin. Therefore, if the pole of the moon tilts toward those signs of the mean ecliptic, it leans toward the north; ?93? and when it does so, it can see Venus below the sun more accurately and more clearly through its latitude, since

that latitude is greater when the planet is at its maximum distance from the sun than when it is at its closest approach to the sun. 125. They are deprived of the sight of the moon, that is. as it moves among the heavenly bodies. For since they inhabit it, as we now imagine, they see it just as we see our earth. 126. What is in question is the apparent diameters, not the true diameters. Hence, when the moon is at its greatest distance from

the earth, its apparent radius is 15’. However, its parallax in that same position is 58’ 22”, or a little less than 60:4 X 15’. But

whatever the size of the lunar parallax is, the earth’s radius would appear to be of the same size, if the observer's eye were on the

moon. Hence the proportion 1s a little less than 4:1; when this is squared, it becomes a little less than for the apparent disks. Thus:

16:1, that 1s, more than

15:1

232. Kepler's "eccentric orbit" would have recalled the ellipticity of the moon's orbit only to such readers of his Dream as were already familiar with the great discovery announced in his New Astronomy. For the remaining readers of his Dream, which deals with the motions of the other celestial bodies as seen from the moon, rather than with the motions of the moon itself, Kepler did not make clear that the moon's path in space is elliptical. In the Epitome, however, he wrote:

“What circles are needed to show the moon's independent non-uniformitv? A single eccentric orbit, nearly circular in shape, that i5, elliptical” (Gesam. Werke, VII, 444:16-17). See Edward Rosen, “The Moon's Orbit in Kepler’s Somnium,” Centaurus

(1966), 11, No. 4.

233. The Lion and the Virgin are two of the six northern signs of the zodiac, as

Kepler

explains

in the

Epitome

(Gesam.

Werke,

Fishes and the Water Bearer are southern signs.

VII,

126:19-20),

whereas

the

Kepler's Notes on the Dream 58’ 22" logistic ?* logarithm 15^ 0” logistic logarithm

2761 138629 95

The proportion ?°* is Double *** this, and obtain

135868 271736

95

This number, as its logistic logarithm shows, is 3’ 587.75 Therefore, if the earth’s disk is 60’, the moon’s is 3^ 58". Since 4’ o" — 1/15 X 60’, the ratio 1s accordingly a little bigger. 234. As contrasted with an absolute number, a logistic number

represented

a

measurement. Thus in his Supplement to the Thousand Logarithms, Kepler explained that “in the third [column] there are logistic, not absolute, numbers; the biggest contains 24°, that is, as many as there are hours in one day, although either

hours or degrees may

be meant indifferently. In the fifth [column]

once more

there are logistic numbers, embracing the sexagesimal series; hence the biggest is 60'." Logistic numbers and absolute numbers were treated as separate branches of arithmetic: "The radius of a circle, it sometimes happens, is presented as divided otherwise than into tenths, hundredths, thousandths, etc. Such non-decimal division is required by the branch of arithmetic which is called 'logistic' " (Gesam. Werke, IX, 361:19-23, 363:18-20). In Kepler's terminology, then, the measurement 58' 22" is a logistic number, which has a logistic logarithm. Kepler wel-

comed the invention of logarithms as an ingenious device to facilitate laborious computations. Since he was concerned principally with astronomical computations involving sexagesimal fractions of the degree and the hour, logistic logarithms

were of prime importance to him. 235. The logarithm “138681” (Somnium, 1634 ed, p. 54) was emended to “138629” by Frisch (VIII, 53:22 up). The correctness of Frisch's emendation may be demonstrated in two different ways. First, 138629 is required as the number from which 2761 is subtracted to yield 135868 as the remainder. Secondly, in Kepler's Thousand Logarithms the logistic logarithm of 15’ o" is 138629.44 (Gesam. Werke, IX, 327:23). In the same work the logistic logarithm of 58’ 19” is 2839.95, and that of 58’ 23” is 2737.12, the difference between the two logarithms being 102.83 (Gesam. Werke, IX, 351:27-29). Since 1/4X 102.83 =25.71, the logistic

logarithm

of 58’ 22" would

venient approximation 2761.

be 2762.83, for which Kepler here writes the con-

236. Kepler's logarithms were based on proportion, as he made clear in the fol-

lowing definition of a logarithm in his Thousand Logarithms: “Express the measurement of every proportion between 1ooo and a number smaller than 1000...

by a number which is placed alongside this smaller number in the Thousand and

which is called its logarithm, that is, the number (arithmos) indicating the proportion (/ogos) which that number, to which the logarithm is attached, bears to 1000" (Gesam. Werke, IX, 297:23-27). Ihe process of finding the proportion 15':58' 22”, that is, of dividing 15’ by 58’ 22", is shortened by subtracting the logarithm of 58’ 22" from the logarithm of 15’.

237. Doubling the logarithm

(15’ 25”, Gesam.

135868 is equivalent to squaring the antilogarithm

Werke, IX, 327:37).

238. The logistic logarithm of 3’ 58” in Kepler’s Thousand Logarithms is 271810.06 (Gesam. Werke, IX, 321:15). The difference between 271810 and 271736 is only 74, where a difference of 1” in the antilogarithm corresponds to a difference of well over 300 in the logarithm.

96

Kepler's Notes on the Dream 127. Ihe moon always turns the same spots toward the earth.

Therefore, the line connecting the centers of the earth and the moon always pierces the moon's surface in the same spot. The inhabitants of this spot always have our earth, that is, their Volva, overhead.**® But in any place which is distant from this spot by a

given number of degrees of a great circle, Volva seems to deviate

from the zenith by an equal number of degrees in the heavens. 128. A revolution of the moon's body occurs in the period of a month. For throughout its entire course it turns the same face toward the earth, as we know from the unchanging permanence of its spots. But the earth, that 1s, Volva, seems to traverse the entire zodiac in the period of a month. The face of the moon also travels along with the earth, turning at one time toward the Crab, and at another time toward the Goat, which is the opposite sign. In other words, the moon revolves.?*?^ However, to those who are on the moon it does not seem to revolve, but they regard it as stationary, just as our earth seems stationary to us. Instead of the moon, therefore, the heavens seem to revolve, in the opposite direction. Conse-

quently, it follows that in the heavens there are also two points,

around which the heavens seem to the moon-dwellers to rotate once a month, as though these points were stationary. They are called the poles.

129. If the moon's

axis remained.

parallel to the

earth's axis

throughout the entire revolution of the moon, we would sometimes see new spots around the moon's northern and southern edge, namely, when we observe the moon in opposition to the sun in the Crab or the Goat. For the line drawn from the center of the earth through the boundary of the tropical zone and meeting the zodiac in one of the two solstitial points intersects the earth's axis at unequal angles. Therefore, it would intersect at the same angles also the moon's axis, 1f this were parallel to the earth's axis. Hence, one of the moon's poles would be visible to us at that time, and at the

opposite time of year the opposite pole would be visible. This phe239. As Kepler pointed out in the Dream

(p. 21, above), Volva stands directly

over the heads of the equatorial mid-Subvolvans. 240. Here in Note 128 Kepler is at pains to explain that by the word converti he means “revolve.” Yet sometimes the idea of rotation is expressed by converti (for example, Epitome; Gesam. Werke, VII, 80:12). However, a comparison of the two

contexts

shows

how

carefully

Kepler

distinguished

in one place and motion from place to place.

between

rotatory

motion

Kepler's Notes on the Dream

97

nomenon 1s not observed. Therefore the axis of the lunar globe is not parallel to the earth’s axis, but is always intersected at right angles by the line from the center of the earth. Consequently the moon’s axis 1s not directed toward those points toward which the earth's axis is directed. The earth’s axis, however, is directed toward what we call the "celestial poles." Consequently it 1s not toward them that the moon's axis is directed.

130. The poles of the lunar globe's monthly revolution and gyration are not the same as the poles of the ecliptic. On the con-

trary, the former revolve around the latter in small circles having a

radius of 5?, and complete one revolution in the reverse order of the signs in a period of nineteen years, as follows. Therefore, since

the lunar poles do not move more than 5? away from the poles of the ecliptic, the lunar poles may be correctly described as around the poles of the ecliptic, and so, also, around the fixed stars which mark the poles of the ecliptic.

131. As the moon revolves, it describes the orbit whose poles we

are discussing. Now the poles of every great circle on a sphere are

always exactly a quadrant's distance away from all parts of the cir-

cumference. Yet the moon’s orbit is not a perfect circle. For at the quadratures this orbit increases its latitudes, that is, it moves farther out toward the poles to which it conforms at the syzygies. Thus its distance from those poles of the syzygies is not at that time exactly a whole quadrant, but nearly a quadrant. However, this lunar path bending around the earth as though the latter were stationary in the center of the universe is transferred by the moon-dwellers, who imagine their own home to be stationary, to this earth, that is, their Volva.

132. It was remarked in Note 127 that every great circle drawn through Volva enjoys the benefit of Volva's immobility, and that the different degrees of the circles are distinguished by Volva’s varying altitude. Among the great circles, however, there is one

which goes halfway between the poles of the moon from west to east. Therefore, also in it places can be distinguished according to

the degrees of Volva's altitude toward the west or the east. But this

is a difference of meridians, or of longitude. 133. For the moon-dwellers the altitude of the pole provides the

same help to observation as on the earth, or not much different. This altitude of the pole can serve equally well to determine the

98

Kepler’s Notes on tbe Dream

latitude of places on all the meridians, since they all converge in the

poles of the moon-dwellers. But although the altitude of Volva 1s observable with the utmost ease, nevertheless, it does not serve equally well on all meridians to determine the latitude of a place. For only on that central meridian of all which is always drawn through Volva, and only on that one of its semicircles which divides the Subvolvans in half, does the altitude of Volva immedi-

ately yield the latitude of the place. But outside this prime meridian

the altitude of Volva must be accompanied by an additional argument adducing its distance from the prime meridian. This is the sort of argument we use in deriving the altitude of our earthdwellers' pole from the altitude of the sun when it is at the equinox but outside the meridian.

134. We do, of course, have lunar eclipses and occultations of

the fixed stars, but this is a very laborious and uncertain method.?*

Moreover, when I wrote the Lunar Astronomy, the declination of the magnet from the meridian was in some repute as though

it were suitable for determining the longitudes ?*? of places everywhere.?* For about that time a certain Frenchman’s Mécorétrie 241. Determining the difference in longitude between two places by comparing

the local sun times at which the same lunar eclipse occurs is a method “suitable for places which are at a considerable distance from each other” (Kepler, Epitome; Gesam. Werke, VII, 246:25-26). 242. Instead of “longitudes,” the 1634 Somnium has “latitudes.” The credit for catching this error belongs to Siegmund Günther (Geographische Abhandlungen, 3, No. 2:287). 243. In 1596 Kepler was told that the former professor of astronomy at Tübingen University, Philip Apian, "had established a new doctrine of finding longitudes from the declination of the magnet. If this is true," Kepler reasoned, "Apian

must surely have discovered or determined the spot to which the magnet points, instead of to the pole .... Had the magnetic pole been definitely located, it would be an easy matter trigonometrically to deduce the declination of the magnet, given the longitude and latitude of a place, or given the latitude and the declination of the magnet, to find the longitude of the place" (Gesam. Werke, XIII, 189:26-29, 40-43). From two observations of magnetic declination reported by De Veer (see above, fn. 22), Kepler concluded in 1599 that "the distance of the

magnetic pole from the celestial pole is 6%°” (Gesam. Werke, XIII, 351:455-56). This separation had not always existed, Kepler believed, for he imagined that the

two poles had originally been one: “The spot toward which the magnet points was the pole of the earth at the beginning of the universe. Since that time the pole

of the earth has moved 65? from its primordial position"

(Gesam. Werke, XIV,

26:188-89; 55:509-13). But his reading of William Gilbert’s Magnet (London, 1600), Kepler acknowledged, brought about “the complete destruction of my speculations about that slow migration of the pole of the daily motion from the

Kepler’s Notes on the Dream

99

had been published.*** But William Gilbert's magnetic theory and places on the earth which

were

assigned

to it at the creation”

(Gesam.

Werke,

XIV, 347:213-15). Having been persuaded by Gilbert, Kepler rejected magnetic

declination as a guide to longitude so completely that when he asked, in Bk. 3 of the Epitome, “How is the difference in longitude of places on the earth determined?" he did not even mention magnetic declination (Gesam. Werke, VII, 244:15-236:43).

Let us now recall that Bks. 1-3 of the Epitome were published in 1618. But magnetic declination as a means of finding the longitude was in some repute when

he wrote the Lunar Astronomy, Kepler says here in Note 134. Hence he is referring to the text and not to the Notes, which he composed between 1620 and 163o, long after he had ceased to believe in an invariable relation between magnetic declination and longitude. This important shift in Kepler' thinking, in conjunction with his use in Note 134 of the title Lunar Astronomy, rather than the more frequent Dream, may help to solve the problem of the stages in which the work was written. It began as a “disputation concerning the moon" (see

Appendix C), and it retained that nature while Kepler still had faith in magnetic

declination as an indicator of longitude. It was only after he had abandoned this faith that he inserted his youthful “disputation concerning the moon" in the larger framework of the Dream. If this attempted reconstruction has not gone astray, the boundary line between the original Lunar Astronomy and the later Dream runs between Kepler's Notes 86 and 87 in his text.

Philip Apian (1531-89) was dismissed from the faculty of Tübingen University because he felt that in good conscience he could not sign the required oath of religious allegiance, on grounds similar to those which later troubled Kepler. The

vacancy created by Apian’s dismissal was filled by his former pupil, Mastlin. For a study of Philip Apian and his father, Peter, see Siegmund Günther, "Peter und Philipp Apian," Böhmische Gesellschaft der Wissenschaften, Abhandlungen, 6th seiles (1881-82) , 27, math.-naturw. Classe, No. 4. 244. Guillaume de Nautonier’s Mecometrie (Toulouse and Vénes, 1602-1604), according to its lengthy title, explained “how to measure longitude by means of the magnet; it teaches a very reliable way, heretofore unknown, of finding the geographical longitudes of all places as easily as the latitudes.” To Nautonier, Kepler addressed a letter in Latin on February 2, 1606, which began as follows: “Your book, written in the French tongue, has reached Prague, too . . . . What has impeded me up to now in studying it from cover to cover has been my very scanty knowledge of the language, which I once obtained in part from French youths in Germany and in part acquired later from books. When I read the epistle which

you address to your readers, I was highly pleased . . . . You urge that the declina-

tion of the magnetic needle from the meridian should be and reported to you. I shall do so with the utmost care after book and grasped the theory of the instruments. For the previous observations." These were then set forth in some

observed everywhere I have mastered your present, listen to my detail by Kepler. He

also transmitted a copy of his Letter about the Solar Eclipse (see above, fn. 115), and suggested that if Nautonier wished to reply, he could do so through the

French

ambassador

at Prague

(Gesam.

Werke,

XV,

No.

372:2-3,

6-9, 46, 61-64,

100-103). Less than a year after he wrote to Nautonier, Kepler gave Herwart von

Hohenburg his candid opinion of the Frenchman's book: "Guillaume de Nautonier, lord of Castelfranc in Languedoc, propounds very brilliant speculations

about the usefulness of the magnet in finding the longitudes of places on the high

100

Kepler's Notes

on the Dream

numerous experiments, when carefully considered, refuted those ineffective and useless efforts.?** For on the globe of the earth there is no fixed point, except the one at the pole, to which seas. But I greatly fear that his plans are useless to those who hold the helm in

their hands. Pilots amid the ocean waves do not hear the voice coming from far away in the heart of the continent clearly enough to guide themselves by it" (Gesam. Werke, XV, 387:23-29). The title page of the original French edition of Nautonier's book, as well as of a partial translation into Scottish, was reproduced in the Papers of tbe Edinburgb Bibliograpbical Society (1895-98), 3:128-31. Flemish and Spanish versions of Nautonier also appeared, as part of the effort of the seafaring nations to solve the baffling problem of finding the longitude in the open water.

For the solution of this problem the Dutch government offered a large sum of gold as a prize. So Galileo was informed from The Hague in 1627 by one of his admirers, Alfonso Antonini, who remarked: “There was a Frenchman who wrote a big book on Mécométrie by means of the variations and declinations of the

magnetized

pointer; but the final upshot is that everything

worth nothing"

(Galileo, Opere, XIII, 379:19-21).

he demonstrates

It will be recalled that, like Antonini, Kepler did not mention Nautonier

name in his Note 134, where do so because he was aware

is

by

he called him merely a "certain Frenchman." Did he that Nautonier had been accused of having imitated

the writings of previous authors, particularly another Frenchman?

This accusation

was published at Paris in 1611 by Didier Dounot (1574-1640), professor of mathematics in the royal academies and author of the first complete translation of Euclid’s geometry into French. In Dounot’s Confutation, which was dedicated to the king of France, the notice to the reader charged that Nautonier’s method had previously been published by Toussaint de Bessard, Dialogue de la longitude estouest (Rouen, 1574). Bessard is one of the 241 authors mentioned by Nautonier (Mecometrie,

fol. «x

4r-v).

245. Gilbert’s Magnet was discussed by Kepler at great length even before he

had finished reading the book. In a letter dated January 12, 1603, Kepler revealed how strong an impression Gilbert had made on him: “This subject [magnetism] was treated by Gilbert extensively, clearly, adequately; he fortified his position on all sides with the most magnificent experiments; he shut the mouths of all those

who would contradict him .... I wish I had wings to carry me to England so

that I might converse with him” (Gesam. Werke, XIV, No. 242: 211-13, 219-20, 390-91). The next year in his Optics Kepler said publicly about Gilbert: "He is the kind of man whose godlike discoveries properly provide all students of nature with the greatest pleasure. Did not a time-consuming sea voyage stop me, my eagerness to learn could entitle me to associate with him without any great difficulty, I hope, since science knows no pride" (Gesam. Werke, II, 135:39-136:2).

The high esteem in which Kepler continued to hold Gilbert was eloquently expressed in the Epitome, where Kepler candidly listed the three men to whom he

felt most deeply indebted: "I erect the whole of astronomy on Copernicus’ hypotheses about the universe, on Tycho Brahe’s observations, and finally on the Englishman William Gilbert’s science of magnetism” (Gesam. W erke, VII, 254:40-42; Great Books, Vol. 16, p. 850). 246. In Bk. 4, Ch. 9, of his Magnet Gilbert asked “whether the terrestrial longitude can be found from the declination?” Acknowledging that “this would be an

accomplishment pleasing to mariners and would bring about a very great advance in geography,” he rejected the current theories as unsound.

Kepler's Notes on the Dream the magnetic

101

needle is directed, **’ but in every region there are

mountainous heights to which the needle is somewhat attracted.?*? 135. Here you have the principal thesis emphasized in a full

statement. Of course, we earth-dwellers think ?*? that the plane on which we stand, and together with it the balls on our towers, remain stationary, but around those balls the heavenly bodies revolve in their travels from east to west. Yet this thought subtracts nothing from the truth, nor does it impose any rule on it. For in

like manner the moon-dwellers, too, believe that their lunar plane

and the ball of Volva hanging up high over it remain in one place, although we know for a certainty that the moon is one of the movable heavenly bodies.

136. This is true not only of the very small and inconspicuous stars but also of the prominent stars of the greater magnitudes. For among the moon-dwellers one night lasts as long as fifteen of our nights, and during it 1/25

of the zodiac,"

that is, 14°,°°? seems

247. The contention that the earth has magnetic poles at a distance from the geographic poles was denounced by Gilbert as a dream and an erroneous opinion (Magnet,

Bk.

1, Ch.

1; Bk. 4, Ch.

13; ed.

1600,

p. 5:6-7,

p.

177:15-16).

Gilbert

reasoned that if such a distinct magnetic pole existed, "in different places on land and sea the variation point would shift eastward or westward in uniform geometrical ratio, and the pointer would alwavs indicate the magnetic pole. But experience shows that there is no definite pole or fixed terminus for the declination on the earth. For the arcs of declination change erratically in different ways" (Bk. 4, Ch.

1; ed. 1600, p. 152:14-9 up). Kepler was so powerfully

influenced by Gilbert

that he accepted the latter's misconception in place of his previous correct idea that there are magnetic poles distinct from the geographic poles. 248. In the New Astronomy Kepler said: "In the magnet, quite clearly, two forces are mingled: one seeks the pole, the other attracts iron. Hence if the compass or nautical needle points toward the pole, but iron approaches it from the side, the needle turns a little awav from the pole and shifts toward the iron. Thus it vields somewhat to its affinitv for the iron while still submitting mostlv to the

pole. This is the reason whv, in Gilbert's opinion, the needle inclines from the pole to the continents of massive size. Therefore the cause of this declination

inheres in the earth's regions, of which the higher, bigger, and more effective mav

be in the vicinity either on the right or on the left" (Gesam. Werke, III, 351:2937). This opinion of Gilbert's was set forth in Bk. 4, Ch. r, of the Magnet (ed. 160o,

p. 153:13-26). P. Fleury Mottelav’s translation of the Magnet into English (New York and London, 1893) was reprinted in Great Books, Vol. 28, as well as by

Dover Publications (New York, 1958), and the Gilbert Club’s translation (London, 1900) was reissued bv Basic Books (New York, 1958). 249. The misprint existamus in the Somnium (1634 ed., p. 56) was corrected to

existimamus by Frisch (VIII, 54:9 up). 5 | 250.

366",

i

Me

251. 360° X Yn = 14°.

102

Kepler’s Notes on the Dream

to cross behind Volva, because,

of course, in one year there are

about twenty-five halves of a natural °°? month. But in 14° surely

some suitable fixed stars occur, as they are dispersed everywhere in the heavens.

137. Whatever the moon intercepts for us earth-dwellers at any

time is intercepted at the opposite time for the moon-dwellers by their Volva, that is, our earth. Now look at my Ephemerides, which I published for years to come,?? and at the end you will see this alternation of the fixed stars. Any one fixed star throughout most of the months of a whole year is occulted once by the moon, but in the following year that star remains free and another star in turn undergoes this experience.

138. The center of the moon deviates from the path of the ecliptic at the most by 5° 18’. To this arc about 15’ are added on

account of parallax, because the moon's radius is a little bigger than one-fourth of the earth's radius. Now the apparent radius of Volva takes up almost four times the apparent radius of the moon; hence it is as much greater as the parallax is smaller, the true radi being related in the same proportion. Thus on both sides the total

reached 1s about 6 1/3°.°°° 139. As a matter of fact the same stars return in less time, but

not in the same order, until after the cycle 1s completed. The reason for this alternation is the rotation of the lunar nodes in the reverse order of the signs in exactly the same number of years.

140. See the diagram suitable for the study of this phenomenon in my Epitome of Copernican Astronomy, page 560.”°°

252. Dy a "natural" month Kepler means the ordinary or synodic month of ap-

proximately 2915 days; 36514 + (16 X 2944)= 15. 253. Kepler's Ephernerides went as far ahead as the vear

179).

1636

(see

above,

fn.

254. In explaining the novel features of his Ephemerides Kepler said (p. 39:2-6): “So far as the fixed stars are concerned, in the interest of astronomers and for the sake of publicly testing the precision of this calculation, in this ephemeris I have carefully noted the days when and places where . . . the moon occults or nearly occults one of the more

prominent stars. This procedure will be

useful to sailors, I believe, for the purpose of obtaining the longitudes of places"

(Frisch, VII, 502:17-13 up). In his notes for 1635 and 1636, the last two years of his Ephemerides, Kepler predicted, for example, that no lunar occultation of the Lion's Heart (or Regulus) would occur throughout the entire year 1635, but that such an occultation would be visible in the southern hemisphere in the first seven

months of 1636. On the other hand he foretold that Asellus Borealis would occulted by the moon in 1635, after January 4, on February 1, and on March but not at anv time during the year 1636 (Frisch, VII, 662-66).

255. 5° 18 + (4 XC 15"). ex 614? 256. Gesam. Werke, VII, 322.

be

27,

Kepler’s Notes on the Dream

103

141. Among us on the day when the moon is new, barely a few hours after it has passed beyond the rays of the sun, it can never-

theless often be seen. Not only is its crescent illumined, but absolutely its entire body. This happens, it is evident, because the earth illumines the lunar hemisphere that is turned away from the sun. For at that time the earth presents to the moon a full circle

illumined by the sun, and reflects the sun’s light to the moon. If this

is true, then analogy teaches us that not very different phenomena are seen by the moon-dwellers on their Volva, which ıs our earth.

Assume that it is new Volva; for its part the moon will be full for

us earth-dwellers. But when the moon is full, everybody knows how brilliantly it adorns the earth (which is the Volva of the moondwellers), especially on winter nights when the moon in its motion through the Crab lights up our earth from on high. Hence there is nothing absurd in the statement that that very moonlight which brings the mountains and nearby plains into our sight at night makes that same plain of the earth (of Volva, for the moondwellers) visible as far as the moon. True, the moon receives and

reflects barely 1/15 of the light received by the earth from that

same sun. But on the other hand the face of the earth is fifteen times ?* more spacious for those who inhabit the moon than the latter is for us earth-dwellers. Therefore there is a balance. Now add the bright crescent shown by Volva, on account of its deviation to one side of the sun’s path, once again fifteen times more brightly to the moon-dwellers than the moon shows its crescent to us earth-dwellers. To this crescent of Volva the words “practically never’ ’ especially apply. For when there is no latitude, there is also no crescent remaining at the moment of conjunction.

142. To the other places on the moon, the sun and Volva appear

simultaneously at the moment of new Volva.?* On the earth,” if the moon’s thin crescent, which it retains on account of its lati-

tude, is not visible because the sun is present in its brilliance, this happens for reasons connected with vision. But for those who live 257. Here Kepler expressed the multiple by quindecim partibus; a few lines fur-

ther on, toward the end of his Note 141, he used quindecuplo for the same relationship, as he did also in the Epitome (Gesam. Werke, VII, 475:2-4). His care-

lessness in this regard should be noted in connection with fn. 225.

258. Hence Subvolvans.

Volva would

be completely

invisible at that time

to the non-polar

259. Kepler's ubi refers to Volva. What precedes ubi in Note 142 describes phe-

nomena as seen from the moon, whereas, in a sudden shift in Kepler's point view, what follows «bi describes lunar phenomena as seen from the earth.

of

104

Kepler's Notes on the Dream

between the poles of the moon’s path and of the sun's path, ^"? the sun is below the horizon at their noon, while the moon is a little above the horizon. Hence it is that much more clearly visible.

143. Day is deemed to begin when the sun first stands on the

horizon. Let the moon be in L, °° its first quadrature.

Ihe

angle

SLC, formed by the lines connecting S, the center of the sun, and

C, the center of the earth, with L, the center of the moon, is a right

angle. SG, the tangent to the body of the moon, will form SGL,

nearly a right angle. Now if a ray such as ST from the center of the sun touches the surface of the earth, the sun will be considered to be on the horizon of T, the terrestrial place marked by the contact. For the same reason, then, the sun will be regarded as also on the horizon of the lunar place G, where SG has its point of

tangency. A straight line drawn from L, the center? of the

moon, through G, the point of tangency, to the earth will indicate the zenith of that place on the moon. Therefore those who then have Volva at their zenith have the sun on their horizon. In other words, at that time they have the beginning of their day.

144. On the other hand, moon-dwellers like those in O, who see

Volva on the horizon at the time of the quadrature, inhabit a re-

gion where CO, the rays of Volva,?* are tangent to the globe of the moon. LO, the straight line drawn from L, the center of the moon, to O, the point of tangency, makes a right angle at O. The

area of tangency spreads out over an entire circle of the body of the moon, a circle which is nearly a great circle. Therefore on it

there will be a point through which the straight line drawn from L pierces the ecliptic. Let this point be O. But beneath the ecliptic, the poles of the ecliptic Hence, if it 1s the time of a quadrature, at the also 1s a right angle, at such a place O, which the ecliptic and Volva on the horizon, the line

for the places lying are on the horizon. moment when LOC has both the poles of LO must come very

260. The poles of the moon's path, Kepler pointed out in Note 130, are 5° from the poles of the ecliptic. These in turn are the poles of the sun's (apparent) path,

and are located about 23° from the earth’s north and south pole. “Those

who

live

between the poles of the moon's path and of the sun's path," therefore, live within 5° of the arctic and antarctic circles. 261. See figure on p. 88, above.

262. The misprint Cezro in the Somnium centro by Frisch (VIII, 55:8 up).

263. See figure on p. 88, above.

(1634

ed., p. 58)

was

corrected

to

Kepler's Notes on tbe Dream

105

close to the sun, and thus the sun then adjoins the zenith and the hour is noon.

145. Actually the globe of the earth does move in space as it

traverses the zodiac in the course of a year. But to the moondwellers it seems to have absolutely no motion in space, because they have no means of observing this motion with their senses. They rather think, therefore, that the sun completes that motion in

the opposite

direction in twelve and a half of their days-plus-

nights. ‘he same thing happens to us earth-dwellers, too, with regard to that same sun. 146. Ihe globe of the earth also rotates around its own axis once in the course of a day. This motion of the earth manifests itself to the eyes of the moon-dwellers. They have no obvious reason to

suppose that the globe of Volva does not itself rotate around its

own axis, but rather that the whole universe

(as 1s believed by the

opinion common among us) and together with it also their own home, the moon, travels around Volva, examining all the parts of

its sphere in succession, even though this is in fact the truth. Take for example the appearance of the spots on the sun. We see them go around the body of the sun in a period of about twenty-six

days.” Who

could ever arrive at the idea that the spots on the

sun are stationary, while that ship of ours, which is called the earth, carries us in so short an interval of time around the sun, revealing to our very selves the various parts of its surface and its spots in succession? Ihe Copernicans themselves, who are convinced that they are carried in a year’s time around the sun, for this very reason are certain that they do not complete this journey in twentysix days, since these are contradictory statements. Therefore vision furnishes us with the most certain proof of the rotation of the sun. And therefore vision attests to the moon-dwellers that their Volva rotates around its own axis. Here, whether their vision be deceived 264. In his Sunspots Galileo said: "All the spots without any variation remain on

the solar disk equal lengths of time, which in my judgment are a little more than 14 days” (Galileo, Opere, V, 203:17-19; Galileo, p. 136). Marcus Welser, to whom

copy of the printed work 656:2-5). On the very dav Maelcote: “The spots remain and therefore, also, the same

Drake, Discoveries and Opinions of Galileo addressed his Sunspots, sent a

promptly to Kepler (Gesam. Werke, XVII, No. Kepler received the copy, he wrote to Odo van at the most 14 days on the visible face of the sun, number of days on the hidden face. Consequently

one rotation takes between 25 and 28 davs"

(ibid., 64:25, 31-33).

106

Kepler's Notes on the Dream

or assert an absolutely correct proposition, the outcome is the same, whichever alternative you choose: reliable evidence is provided that the lunarians, if there are any, must be convinced that Volva rotates, the statement that was to be proved. But so far as that more secret purpose of this tale is concerned, a delightful retort is created for us. Everybody screams that the motion of the heavenly bodies around the earth and the motionlessness of the earth are manifest to the eyes. To the eyes of the lunarians, I reply, it is manifest that our earth, their Volva, rotates, but their moon 1s motionless. If it be argued that the lunatic senses of my lunarian

people are deceived, with equal right I answer that the terrestrial

senses of the earth-dwellers are devoid of reason.

147. From the spots on the moon we draw an inference about the nature of the moon's surface as being made up of water and dry land. Nor is the inference unsound. For by absolutely certain principles of optics we prove that that variety of spots and light is

connected with the roughness and smoothness of the surface: what is bright, is both high and hilly; what is dark, is both flat and low. But this contrast is associated with the difference between land and water. Ihe foregoing is what we earth-dwellers say about the surface of the lunar globe.

On the other hand, by reversing this same reasoning, I grant my

moon-dwellers that because the earth’s surface has both mountains and seas, it presents to the moon-dwellers the appearance of dark

spots on a bright background. See Note 154. 148. The surface of the earth in fact rotates around its axis from

west to east with regard to its center. But with regard to the spectators who live on the moon, the part of the earth’s globe that is turned toward the moon seems to be traveling from east to west. ‘This is in accordance with the axiom in Aristotle's Mechanics ?95

that the opposite parts of a circle (or sphere) seem to go in oppo-

site directions °°* when they are viewed from outside the circumference of the circle.

265. Modern scholars regard the Mechanics, which was included in the collec-

tion of Aristotle’s writings, as a product of Aristotle’s school, rather than of the master himself; see Aage G. Drachmann, The Mechanical Technology of Greek and Roman Antiquity (Copenhagen: Munksgaard; Madison: University of Wisconsin Press, 1963), p. 13. 266. “A circle has opposite movements at the same time, one end of the diameter... moving forward, but the other... . backward” (Pseudo-Aristotle’s Mechanics, 848° 20-22).

Kepler’s Notes on the Dream 149. If the sun’s

“night,”

107

presence is to be called “day,” and its absence

surely its very

prolonged

stay over the horizon

of the

places on the moon requires subdivision into smaller parts. Our day together with its night is only 1/29 of the lunar day-plus-night,

and even a little shorter. If this quite brief interval is divided into twenty-four parts for the sake of convenience, how much more necessary will be the subdivision of so long a day as that. Moreover, nature has indeed robbed us earth-dwellers of the ability to

distinguish with our eyes what is judged by man’s mind and opinion. For nowhere is there anything which returns to its original place after rotating during the course of one of our hours. But on

the moon the Subvolvans have this motion of their Volva around its own axis occurring in front of their eyes. This motion brings back the spots on Volva in the same order, and it does so fourteen times in one lunar night. That this observation is overlooked by the moon-dwellers is, therefore, not at all probable. But this very circumstance makes it possible to estimate to some extent the in-

digence and loneliness of the Privolvans: deprived of the sight of Volva, they lack even this means of telling time.

150. Here we must distinguish three rotational periods of the

surface of the earth or Volva. The first 1s the period in which the same place on the surface returns to a position below the same fixed

star; this period 1s a little shorter than one of our natural days-plus-

nights. Ihe second period marks the return to the line drawn through the centers of the sun and of the earth from the same region of the earth; this period is exactly equal to, and indeed is the cause of, the natural day and night. The third period marks the return to the line drawn from the center of the earth through the center of the moon; this last period is the one that brings the spots

on Volva back into the moon's field of vision. Its length may be computed as follows. In 76 years there are 940 lunations, **’ dur-

267. If we start with the sun and moon aligned, "the moon completes twelve revolutions with respect to the sun somewhat sooner than the sun returns to the beginning of the journey. Therefore a longer time is needed to make the joint return

more

nearly

simultaneous.

Hence,

from

the

observations

of

the

pagans

arose the three-year cycle, containing 37 months; this not being very precise, the eight-year cycle of 99 months, so that the hundredth

month

begins the following

eight-year cycle; the eleven-year cycle of 136 months; and more accurate than all these, being made up of the last two, the nineteen-year cycle of 235 months. Since

a difference of one-fourth of a day still remains before the new moon returns to its original

position,

Callippus

years and 940 months"

quadrupled

the

number,

(Kepler, Epitome; Gesam.

forming

a period

Werke, VII, 484:23-32).

of 76

108

Kepler's Notes on the Dream

ing which the fixed stars complete 19 X 1465 7 = 27,835 revolutions, or 10,020,600°. But in this period of time 27,759 of our days elapse.?° Hence

subtract 940 lunations, and 26,819 days are

left.2”° So many times do the same spots on Volva return as seen by the moon-dwellers. Divide the total number of degrees by 26,819; the result is 373 2/3?.?! So many degrees of the equa-

tor ??? pass while the moon-dwellers see the spots on Volva return in order. In other words, one moon-dwellers’ hour is as long as a

little more than 1 1/30 of our days-plus-nights,"? that is, almost

twenty-five of our hours.”

151. For, this same rotation of the earth generates in us earth-

dwellers the image of the first movable sphere, the motion of which is conceived by the astronomers to be perpetually uniform.

152. See in Note

uniformity dwellers.

109 both the fact and the cause of this non-

in the sun's motion

as it 1s observed

by

the moon-

153. The two halves are the two parts of the world. One is the

Old World, in which Europe, Asia, and Africa are united. The other is the New World, whose parts are the Americas, North and South. However, I restricted this separation into halves rather to the north. I did so because Magellan’s region, which is very extensive in the south, is unknown and is believed to be an unbroken

continent stretching into both hemispheres,

well as the Old World.

the New

World

as

154. I referred to this mistake in my Conversation with the Sidereal Messenger of Galileo, which I published at Prague in the year 1610, and at the same time I also added the necessary correction.? Galileo taught me that the high and rugged places on the 268. 76 years — 19 X 4 years; in four years the fixed stars 4 X (365 1/4 + 1) times = 1465 times.

(apparently)

revolve

269. 76 X 365 1/4 — 27,759.

270. 271. 272. above. 273. 274.

27,759 — 940 = 26,810. 10,020,600 — 26,819 = 373.64. For tempora aequatoris, meaning

“degrees

of

the

equator,”

see

fn.

210,

31/30 X 360° = 372°. 1 hour = 15°; 25 X 15° = 375°

275. "On page 251 of my book [on Optics] I cited the opinion of Plutarch, who regarded those ancient spots on the moon as lakes or seas, and the bright areas as

continents. I did not hesitate to oppose

him

and to reverse

his interpretation, by

attributing the spots to continents, and the puritv of the bright region

to the

Kepler's Notes on the Dream

109

moon are not the spots but the bright area, whereas the water flow-

ing into the lower depths darkens and takes on the appearance of spots.*’° In the same way, therefore, we must say about the earth’s globe, too, that the ocean and the seas lying between the lands look dark, whereas

the continents

and islands shine brilliantly by the

light of the sun. I had previously held the opposite opinion, because

the surface of the earth assumes various colors, while the waters were thought to have no color. But every color (except white) is a

step toward black. Reflected sunlight does, in fact, resemble the darkness of the surfaces from which it is reflected. A second argument was furnished by water. For whenever anybody looks at surfaces of land and water lying next to each other, the land always looks dark whereas the water gleams. In my Optics, page 251, see the experiment which I performed while observing the Mur River from a certain Mt. Schockel ?” in Styria.7? I thought that the

effects of a liquid .... I even founded a new astronomy for the inhabitants of the moon, as it were; in plain language, a sort of lunar geography. Among its

basic propositions was this thesis, that the spots are continents, while the bright

areas are seas. My

motive in contradicting Plutarch in this regard may

be seen on

page 251 of my book [on Optics]. I there report an observation which I performed on Mt. Schóckel in Styria. From my vantage point the river below looked bright,

and the land darker. But the flaw in my reasoning is indicated in the margin of the very next page” (Rosen, Kepler’s Conversation, pp. 25-26). Giorgio Tabarroni re-

cently made the first translation of Kepler’s Conversation into Italian 1964-65, 32-33; revised version, Pubblicazioni versitario di Bologna, 1965, 9, No. 3).

276. Addressing

dell’ Osservatorio

Galileo directly in the Conversation,

Kepler

(Coelum,

astronomico

went

on:

uni-

“My

book [on Optics], consequently, does not prevent me from agreeing with you, as you adduce mathematical arguments against me in favor of Plutarch with brilliant and irrefutable logic .... You have proved your point completely. I admit that the spots are seas, I admit that the bright areas are land" (Rosen, Kepler's Conversation, pp. 26-27). In his Sidereal Message Galileo said that the moon's "brighter part most fitly represents its land surface, but its darker part the watery surface," and that “the moon has its own atmosphere surrounding it" (Galileo, Opere, III, 65:18-19, 95:37; Drake, Discoveries and Opinions of Galileo, pp. 34, 58). This opinion of Galileo was known to Kepler, as an avid reader of the Sidereal Message, in 1610.

Six vears later, in a private letter, Galileo denied that there is water on the moon (Galileo, Opere, XII, 240:20-21). But this private letter was not made

public dur-

ing Kepler's lifetime. In fact, it was first published in an edition of Galileo's collected works (Florence, 1718, III, 474-75) which appeared nearly a century after

Kepler's water on 277. In latinized

death. Hence Kepler did not know that Galileo denied the existence of the moon. the Sommium (1634 ed., p. 62) the name of this mountain was given in a form as “Seculo,” which was changed to “Schekel” by Frisch (VIII, 57:7

110

Kepler's Notes on tbe Dream

cause of the sheen was the mirror-like smoothness of the surface of the water ?'? as contrasted with the unevenness of the land. In

Chapter 1 of my Optics I devote a good deal of space to a consid-

eration of these causes.?° At the present time, therefore, I have to refute those arguments

(as I did briefly also in my Conversation, page 15),??' and I have to give reasons in support of the opposite opinion, which I cited in

my Conversation as having been put forward by Galileo. So far as the colors of land are concerned, then, you would certainly be more correct, or at least equally right, in saying that all colors ex-

cept black are steps toward pure light. With regard to the absence

of color in water, that statement is denied by Aristotle in his little

up). In shifting to the German name, Frisch made the Dream conform to Kepler's practice in the Optics and Conversation as well as in his Latin correspondence (Gesam. Werke, II, 220:33; IV, 298:5; XIV, No. 239:515, 609-10; XV, 265:1014).

278. "In the year 1601, when I had returned to Styria for the sake of a small business matter, I climbed quite a high mountain, called Schöckel . . . . Looking

down on the other hills in the region below for more than ten German miles gave me the same impression as if I were beholding a meadow where the hay was stacked in rows. As I watched from this mountain, the earth presented itself with

unbelievable clarity. Suddenly a cloud arose and When I stretched out a sheet of paper, in many of thrown on it from below than from above. On the the sun showed more light when the cloud covered was exhibited by the whole

land, some

cut off my view of the sky. its parts it showed more light other hand, the side lit up by the mountain. And this clarity

of it darkened

by forests, some

gleaming

with grain and grass, while elsewhere it was ruddy with widespread fallow. The

Mur River, cutting a groove through the middle of the area, was overflowing and boisterous at that time. Yet its extraordinary splendor easily surpassed the misty

clarity of the land. These impressions occurred because the lofty mountain had raised me somewhat straight up, so that more nearly vertical ravs could reach me from the ground below. What would not have happened had I been able to inspect the entire earth along almost perpendicular lines? These observations furnished evidence to my eyes that a greater brilliance usually arises from water than

from land” (Kepler, Optics; Gesam. Werke, II, 220:31-221:11). Kepler described his ascent of Mt. Schóckel also in a letter to David Fabricius, dated December 2,

1602 (Gesam. Werke, XIV, No. 239:514-36). 279. See fn. 288, below.

280. The smoothness and roughness of surfaces as factors influencing the quality

of reflected light were discussed by Kepler in Ch. 6 of his Optics (mainly Gesam. Werke, II, 203, 218-20), and not in Ch. 1. Was a "V" omitted from "VI," leaving

only "I" in the 1634 Somnium, p. 63? 281. "Obviously the river did not, like the land, shine by light received from the

sun, but by light reflected from the illuminated air. Hence my analysis of the causes of the phenomenon was also unfortunate. For, in opposition to the doctrine

of Aristotle's book On Colors, I asserted that water partakes of black less than

earth does. Yet how could this be true, since earth turns darker when with water?" (Rosen, Kepler's Conversation, p. 26).

it is soaked

Kepler's Notes on the Dream book

On

Colors?”

where

he explicitly

III

defends

the proposition

that the color of water inclines toward black.?® He uses an argument from the sense of sight: all land is darker when it is wet with rain, whereas it gleams more brightly when the moisture has been

dried up by the heat of the sun.?** I added another experiment

from things at hand when a ?** Jearned man, standing near me on

the bridge at Prague, impressed upon me the brightness of the

water in order to overthrow Galileo’s assertion.28 For I told him

to look at the images of the houses in the water and to compare them with the direct view of the houses themselves: for there is an obvious

difference

in brightness,

the images

in the water

being

darker. In this way, therefore, my first argument concerning the colors of land and water was weakened and reversed. The second argument, pertaining to reflection, is of the sort whose force I destroyed in another passage of the Optics, where I discussed the light of the moon.?® For if we apply the example of water seen close by to round bodies at immense

distances, we stray very far

282. Like the Mechanics in the Aristotelian corpus, this work On Colors is now believed to have emanated from a successor of Aristotle rather than from the master himself. 283. "All water in the course of time . . . gradually turns black" (794^ 26-28). 284. “All the parts which

are always

under

water

turn

black

. . . but what

is

drained and exposed to the sun becomes green, because yellow is mixed with the

black" (794°32-795°2). The ancient Aristotelian author was actually talking about a cistern and not about "all land when it is wet with rain," as Kepler under-

stood the passage.

285. The misprint quisqiam in the Somnium (1634 ed., p. 63) was corrected to quisquam by Frisch (VIII, 58:6). 286. The misprint assertionem in the Somnium (1634 ed., p. 63) was corrected to assertationem by Frisch (VIII, 58:7).

287. In his Optics Kepler rebutted the contention of those who "say that if the sun sends its light to the moon, that light will be transmitted to us by reflection. Consequently

turn our eyes it will follow see an image around either

we

do not see the light of the moon.

On

the contrary,

when

toward the moon, we receive the rays of the sun. If this is that the moon is a convex mirror. Therefore in the moon of the sun. Moreover it will not be possible to see the sun's when the moon is full or when its body is divided in half.

cording to the law of reflection, reflection occurs

only at that one

point

we

granted, we will rays all For acon the

body where the angles made by the incident and reflected rays with the sphere can be equal. But we do not see the sun's image in the moon. Nor is the moon lit up in one fixed place where the angles can be equal. On the contrary, sometimes

its whole

body

is visible, sometimes

half, and

sometimes

a crescent

at the outer-

most edges. Consequently it follows, they think, that the moon does not shine by

rays coming from the sun" (Gesarn. Werke, II, 202:22-35). To destroy the force of this argument Kepler relied on what he called "communicated light" (see fn. 289, below).

112

Kepler's Notes on tbe Dream

from the path by adducing as a cause that which is not a cause. For when water which lies near land shines, it does so as a result, not of its own brightness, but of the brightness of the air illumined by the sun, whose brilliant rays descending from all directions are reflected to our eyes. For just spread a sail in back of the water so that the brightness of the outer air is intercepted. Immediately you will see this shining of the water stop. This refutation of my argu-

ment I added in the margin of page 252 of my Optical Part of Astronomy while I was rereading it." However, the heavenly

bodies illumined by sunlight and beheld at a distance are seen, not by the sun’s rays reflected according to a law of optics and mirrors, but by the sun’s communicated light (as I called it in my Optics), which is converted into the bodies’ own light by the unevenness of their surfaces.2 Moreover, by virtue of its definition this communicated light is stronger on land than on water. This is

enough to refute the opposing argument. In favor of the correct

opinion, which holds that the spotted parts are like seas and lakes, whereas the bright parts are like a dry continent or islands, you have completely convincing arguments in Galileo’s Sidereal Messenger,*! in my Conversation with him, page 16,°° in my 288. “A contributing cause [of the river’s brightness], however, was the daytime

clarity of the air. Since this surrounded the river on all sides, its rays could like-

wise be reflected from the water’s smooth surface in all directions, and thus also to me on the mountain” (Gresam. Werke, II, 221:margin). 289. In addition to incident, reflected, and refracted light, Kepler said, “I introduced a fourth kind of light, to which I assigned the name ‘communicated light.’ It originates in reflected and refracted light” (Gresanı. Werke, II, 202:41-203:2). 290. “Students of optics say little about this fourth kind of light, which we may call ‘communicated light.’ For light, both reflected and refracted, is nevertheless the

light of that object on which it is incident and where it undergoes reflection or refraction. But this light now becomes somehow the light of that surface which it

has illumined”

(Kepler, Optics;

Gesam.

Werke,

II, 31:33-36).

In the supplemen-

tary notes appended to his Optics, Kepler added the following explanation:

“As

this fourth kind of light, namely, communicated light, arises where sunlight is transmitted from only one side, so colored surfaces make it their own, whether they are smooth or rough" (Gesanı. Werke, II, 367:30-32). 291. Galileo, Opere, III, 62:18-71:14; Drake, Discoveries and Opinions of Galileo, pp. 31-40.

292. The moon's "bright areas are broken up bv many cavities; the bright areas are bounded by an irregular line; the bright areas contain great peaks, on account of which thev light up sooner than the neighboring region. Where thev face the sun, they are bright; where they face away from the sun, thev are dark. All these

characteristics suit a dry, solid, and hand, the dark spots, known since

high material, antiquity, are

but not a fluid. On the other flat. The dark spots light up

Kepler’s Notes on the Dream

113

Copernican Astronomy, Book VI, page 831,°° and in Note

above. The foregoing remarks having shall now explain the reasons for scription. First, I made the aspect I thought, as I have said, that land

147,

provided the necessary warning, I the individual details of this deof the Old World darker because is dark. I called the spots “almost

continuous,” because Europe is connected with Asia in Scythia,

and Asia with Africa in that part of Arabia which Egypt and Palestine.

lies between

155. Ihe half in which the New World lies I called “a little lighter” in aspect because of the same error. The New World has

later—a fact which proves their low elevation—when the surrounding peaks are already aglow far and wide. When the dark spots are illumined, a certain shadowlike black effect differentiates them from the peaks. The boundary of the illumination in the dark area is a straight line at half-moon. These

characteristics, in turn,

belong to a liquid, which seeks the lowest levels and on account of its weight settles

in a horizontal

position”

(Rosen,

Kepler’s

Conversation,

pp.

26-27).

293. "What are the spots on the moon? It is impossible to make any absolutely certain pronouncement about bodies so far away. Nevertheless, the spotted parts of the moon agree in three respects with the seas and lakes on the globe of the earth, whereas the bright and shining parts of the moon

agree with the mountains,

cliffs, promontories, and beaches of our firm land. For the moonspots are deep, like our lakes and seas, and have a

dark, as all wet places among bright parts on the moon

level surface, like a liquid; and finally, they are

us are blacker than when

they are dry. But the

are high and lofty and rugged, like our mountains

inter-

sected by valleys, and more brilliant because they are dry. "How do you demonstrate these properties of the various parts of the moon? From the moon’s phases. For if you look with a Dutch telescope at the line which

bounds the phase on the inside, it is not a perfect ellipse in the crescent or gibbous

moon, nor a perfectly straight line in the half-moon. For in the spotted parts the width of the phase is shorter, whereas

it is longer in the bright parts. The

whole

line looks as though it were toothed or notched. These are arguments for a difference in the height of the spotted and bright parts. Thus, in the part turned away

from the sun, near the line which divides the dark portion of the disk from the bright portion, there are brilliant points, as though they were mountain peaks lit

up first by the sun. These points belong not to the spotted, but to the bright parts of the moon. This fact becomes clear to anybody who waits until the spotted parts are completely lit up and added to the width of the phase. On the other hand in the brighter part, when it is lit up, again in the vicinity of the dividing line, there are black points, as though they were valleys in shadow or caves. But these are proofs of ruggedness. Yet those bright or intensely dark points are lacking in

the spotted parts. This is a proof of a level surface. Finally, in the bright parts there is an extraordinary knob, which is immensely bright, as though it were a

huge mountain covered with snow. This is a proof of brightness in the elevated regions.

By

contrast,

blackness

and

darkness,

the

accompaniments

of

wetness

among us, remain in the parts of the moon which are low down and spread out flat” (Kepler, Epitome; Gesam. Werke, VII, 474:6-31)

114

Kepler's Notes on the Dream

more seas and great expanses of ocean, of both the inner and outer ocean, ?* which compress the middle of America into a narrow

isthmus ?** and, so to speak, strangle it.*”°

156. Ihe Brazilian, Atlantic, Duecaledonian,?" Arctic Ocean,"?? extending to the Anian strait?? and spreading out into the ocean of Japan, the Philippines, Moluccas, and Solomons.

157. With reference to the so-called “belt” or Atlantic Ocean. 158. Africa. 159. Europe.

160. tary. 161. 162. 163.

Sarmatia,

Thrace,

the Black

Sea regions,

Muscovy,

Tar-

Britain. Scandinavia, or Denmark, Norway, and Sweden. Asia, Tartary, Cathay, China, India, etc.

164. Asia of course extends eastward from Europe. But because

the moon moves around the earth in the same direction as the earth’s surface around its axis, the result is that the lower hemisphere of the earth or Volva seems to the moon-dwellers to be traveling westward.

165. The two oceans, according to the mistaken hypothesis, of

course. 166. The American continent.

167. South America.

294. Atlantic and Pacific, respectively.

295. Panama. 296. This picture of the Atlantic and Pacific Oceans teaming up to choke America by its thin neck in Panama vividly illustrates Kepler’s lively imagination and

his deep-rooted tendency to conjure up living creatures.

297. “Beyond the northern side of Albion, the island of Britain, lies the ocean called Duecaledonian” (Ptolemy, Geography, II.3). This is the only occurrence of "Duecaledonian" in all of ancient literature. Hence the name must have looked

strange to sixteenth-century geographers, who uniformly adopted what seemed to them a more likely form “Deucaledonian.” This is what Kepler wrote, and he was followed by Frisch.

298. These conventionally distinguished parts of one long, continuous body of water are what Kepler meant by his "belt."

299. For an account of how the mythical "Strait of Anian,” connecting the Pacific Ocean with the Arctic Ocean, was concocted out of a misinterpreted passage in Marco Polo, see Henry R. Wagner, Spanish Voyages to the Northwest Coast of America in the Sixteenth Century, California Historical Societv, No. 4 (San Francisco, 1929), p. 126, and The Cartography of the Northwest Coast of America to the Year 1800 (Berkeley: University of California Press, 1937), Pp. 53, 426.

Kepler's Notes on tbe Dream

IIS

168. Nicaragua, Yucatan, Popayan.???

169. Africa. 170. 171. 172. 173. of the

See Note 164. For of course Brazil faces eastward toward

Brazil. North America. Magellan's region. When the sun is in the Crab, B,?°! the pole of the earth or first movable sphere, that is, of Volva's rotation, is turned

only 6615? away from the sun, that is, by / SCR, and so also from the center of its own disk, which is seen at N by the moon-dwellers along a line through the centers of the sun and Volva. Therefore Volva's disk TR extends beyond its pole B by 2314 °, which are, of course, seen at an angle. Hence, if the radius CR of the disk is taken to be 60’, a line C] from the center of the disk to a place at the pole

B is 55’. 174. Thule or Iceland; but this identification was based on the mistaken hypothesis that the dry parts of the earth’s surface darker than the wet parts.

are

175. Inthe northern ocean. 176. Ihe top of Volva’s disk is grazed by the Arctic Circle. But

Iceland lies on the Arctic Circle. Therefore in any one rotation of Volva it comes once to the top of the disk, when the sun is in the Crab.

177. Asin Notes 169 and 164. 178. For the following reciprocal statements hold true: if the

sun in the Crab 1s always visible to all the inhabitants of the Arctic Circle throughout an entire rotation of the first movable sphere, then the Arctic Circle, likewise, will be always visible either to the sun or to an observer stationed, as the moon-dwellers are, on the line drawn through the centers of the sun and of the earth.

179. For a plane which is drawn through the centers of the

moon and of the earth, and which intersects the circumference of the ecliptic at right angles, at those times passes also through the

poles of Volva’s rotation. But when the sun is at the equinoctial

points, Volva’s pole stands to one side of this plane. The latter, 300. Today “Popayan” denotes a university town in Colombia, but in Kepler’s time it was the designation of an extensive province of Spain’s colonial empire in the Americas. 301. See the figure on p. 88, above.

116

Kepler’s Notes on the Dream

therefore, cuts the equator of Volva

at oblique angles at those

times. Moreover, it is amusing that this same situation is observed also in the sunspots, as I wrote in my letter to Bartsch in 1629 °*” concerning the observations of the Most Illustrious Prince and Lord, Philip, Landgrave of Hesse.??? 180. The moon-dwellers must ascribe an annual motion to the

poles of their Volva because they are unaware that they are carried

around together fixed stars. True, stars throughout are at a distance

with the the from

their Volva in an annual motion below the axis of the earth points toward the same fixed entire year. Nevertheless, the poles of Volva the pole of the ecliptic. As the earth together

with the moon travels through the ecliptic, the earth always main-

tains the same distance from the poles of the ecliptic. But sometimes it approaches the fixed stars where the pole of Volva 1s, and

at other times it draws away from them. As a result, the position of Volva’s pole seems to be in turn on the near side and on the far side of the pole of the ecliptic, and thus to revolve around those poles of the ecliptic. 181.

The

variation

in the

diameter

of Volva

as seen

from

the

moon is exactly the same as we impute to the lunar parallax. Hence, 302. For Kepler’s Reply to Jacob Bartsch’s Letter (Zagan, 1629), see Appendix A, p. 181, below. From Zagan, on March 2, 1629, Kepler wrote to Bernegger: “Take a look at a gav sort of writing, a letter, not on wax like the ancient letters, but made entirely out of lead, which I assembled with my own hands, and sent to

Görlitz to be printed” (Gesam. Werke, XVIII, 386:61-63). From Görlitz some five wecks later Kepler informed Bernegger: “I came to Görlitz, seven miles from Zagan,

for the sake

of my

Reply”

(ibid., No.

1105:2-3).

When

Kepler’s

Reply

was published, its title page announced that it had been composed with “tvpe of

Zagan” (typis Saganensibus). 303. “I journeyed to Butzbach

with

Philip,

the

Most

Illustrious

Landgrave

of

Hesse, and I spent time inspecting that most esteemed Prince’s instruments and astronomical activities . . . . In an open and spacious place a pole about thirty feet high 1s made fast. Through a pulley at the top a rope is passed. The rotation of the wheel raises a huge tube fifty feet long, which six strong men with a struggle lift to the top of the pole. An aperture in the tube has the size of a pea or a lentil or even a seed of millet. Through the aperture the sun’s rays descend to a white screen confronting them. On

this screen, which

closes the hollow

tube at its bot-

tom, the sunspots are clearly seen. They are formed by the bare aperture, without the interposition of any convex lens. The images recorded at noon on many successive davs reveal that the spots move in a line. This line is perpendicular to the meridian at the solstices. At the equinoxes it is inclined at an angle complementary to the obliquity of the ecliptic, but at opposite equinoxes in opposite directions. Thus this line of motion always intersects the plane of the ecliptic” (Kepler, Replv to Bartsch; Frisch, VI, 581:18-3 up).

Kepler’s Notes on the Dream

117

when Volva is at its greatest distance from the moon, its radius is

58’ 22", but 63’ 41” at its least distance from the moon, when the

sun is moving rapidly. When

we are at our greatest distance from

the moon, its apparent radius is 15^; 4 X 15’ = 60°.

182. Ihe moon hides the sun from us, while the shadow on the moon is cast by ourselves, that is, by our globe, the earth. In like manner, the shadow 1s cast on our earth (that is, on their own Volva) by the moon-dwellers themselves up there, that is, by their own moon, while they are deprived of the sun by their own Volva or our earth down here. 183. Nevertheless, for us, too, at that time the moon loses some of its color, especially in the region closer to the shadow.

184. At the time when the penumbra's *?* center, which is generally occupied by the true umbra of the moon, does not encroach

on the earth's disk; or also when it does encroach, but there 1s no umbra of the moon, whereas a residual circle of the sun remains.

Yet in the first case, although

the moon-dwellers

see no deep

shadow on the disk of their Volva, nevertheless at its edge, which the penumbra enters, they observe some faint light and darkness. In the second case, if the center of the umbra does pass over the earth's disk under the indicated circumstances, around the center they see a half-shadow, as though it were cast by a thin cloud or by a transparent veil, and as though it had indefinite boundaries. Similarly among us on the earth, balls?" on high towers project on 304. “Penumbra,” as a concept and term, was contributed to science by Kepler in his Optics (Gesam. Werke, II, 211:8, 28-29). To Herwart von Hohenburg,

who inquired about “penumbra,”

Kepler cited this passage “where

I myself in-

vented the new terms" (bid. XVI, 177:5-9, 188:7-8). "What is meant by the terms ‘umbra’ [or ‘shadow’] and ‘penumbra’ of the moon? By the term 'umbra' of the moon is meant the entire circular portion of the earth’s disk . . . for which

the sun is totally darkened by the moon. But the ‘penumbra’ is the entire portion of the earth's disk or surface for which some part of the sun's body is darkened at

that

instant"

(Kepler,

Epitome;

Gesam.

Werke,

VII,

497:31-498:2).

Kepler

re-

stated these definitions with the utmost clarity and illustrated them with a diagram in his unfinished Hipparchus, which was first published by Frisch, III, 523-24; cf.

also Gesam. Werke, XVII, 410-11:199-200. 305. In his Note 135 Kepler mentioned pilas im towers"), and then used the same word pilam for the where Kepler referred to a penumbra coming down towers" (Gesam. Werke, XVI, 188:17). The shadow priately compared with the moon's shadow. Towers

cal superstructures were

world.

(and still are)

a common

turribus (“the balls on our ball which is the earth. Elsefrom "the balls (globis) on cast by a round ball is approsurmounted by nearly spheri-

sight in Kepler's part of the

118

Keplers Notes on tbe Dream

the ground below them shadows which are not deep but are mixed with the rays of the sun.

185. Yet do not forget that our new moon occurs at the same

instant of time as their full Volva, and our full moon as their new Volva. 186. For the disk of the earth (or of their Volva) has a radius

varying between

63’ 41" and 58’ 22". But the moon's shadow,

which causes the eclipse of their Volva for the moon-dwellers, on account of the sun's size narrows down from the moon to the disk of Volva, so that its radius never exceeds 1’ 22", and frequently is zero.’

187. Never bigger, that is, than 1/46 of the diameter of Volva.

188. On account of the weakening of the sun’s rays. I had in mind what happens in a closed room into which the sun shines through a very tiny hole. But there the fringe usually is red, be-

cause it is surrounded by complete darkness and the sunlight is ın-

side the fringe, so that the contrast is very clear. But on the disk of Volva the shadow of the moon is on the inside and is of negligible

proportions, whereas on the outside the whole disk of Volva is lit

up. Therefore the redness must vanish in relation to the surrounding brightness. See how anxiously I worry about correcting my statements lest some recent observer of these phenomena come down from the moon and prove me wrong. 189. How shadow appears on earthly terrain lit up by the rays of the sun is an experience available to everybody who looks down from high places at noon in the summertime. For it is the same earth which we earth-dwellers inspect at close range and which, under the name of Volva, the moon-dwellers observe from a distance. Nevertheless, the place under shadow will be darker when an eclipse of the sun involves a complete blackout, as sometimes happens on account of the condition of the air or of the celestial

ether around the sun; see my Epitome of Copernican Astronomy, page 895.°"'

306. When the shadow cast by the moon is not long enough to reach the earth, the radius of the moon’s shadow on the earth is zero.

307. "Why don't all total eclipses of the sun produce such complete darkness that night exists instead of day? . . . Around the sun, not here in our atmosphere,

but in the lit up by emanating darkness.

region of the sun, a thick substance sometimes surrounds the the sun's rays. It appears even when the sun is eclipsed, in a circle and projecting so much light that there cannot This matter does not alwavs surround the sun. Therefore,

sun and is as a flame be absolute when the

Kepler’s Notes on the Dream the and we the

119

190. As in Notes 164, 169, and 177, above. For, the surface of earth, the moon stationed above it on the way toward the sun, the moon’s shadow projected onto the earth’s surface, which imagine the moon-dwellers to be observing, all move in one and same direction.

191. See the diagrams of solar eclipses considered from every point of view, at the beginning of my Ephemerides.?° For those

diagrams are fully adapted to illustrate these eclipses of their Volva as seen by the moon-dwellers, since in these diagrams, too, the ob-

server is imagined to be on the moon as required by the demonstrations. Assume an interval of an hour, with 15° of the terrestrial

equator rotating in the middle of the earth’s disk 44??? But 1/2? of the lunar globe will pass by, and the moon's shadow will cover a little more on the earth's disk, for example, PC. But one-half on the lunar globe equals approximately 60 X 1/2 on the earth, according to the ratio of the diameters of the earth's globe and the moon's sphere. In one of our hours, therefore, the moon's shadow PC

crosses more than 30? of the terrestrial equator on the earth's disk, on which only 15? of the surface of the earth's globe rotate. Thus

the shadow CP 1s twice as fast as those parts of the earth which are

nearest to the disk’s center A, and which ?!? are turned directly

ether around the sun is clear and pure, and this brilliance is also missing at that time, together with the eclipsed sun daylight, too, must be completely obliterated" (Kepler, Epitome; Gesam. Werke, VII, 508:42-509:5). 308. These diagrams were reproduced by Frisch

577, 587, 598, 603, 614).

(VII, 506, 530, 538, 550, 559, 573,

309. See the figure on this page, which is reproduced from the Sommum,

ed., p. 67. 310. The misprint Aquae in the Sommium

quae by Frisch (VIII, 60:18 up).

1634

(1634 ed., p. 68) was corrected to A,

120

Kepler's Notes on the Dream

toward the moon-dwellers. However, the shadow is incomparably faster in R or S, the parts where the earth’s equator slopes

down at F and G, the edges of the visible disk. 192. At that time the Rudolphine Tables had not yet been prepared.?'! Nevertheless, see under the year 1633, April 8 and October 3, examples of nearly central conjunctions.?? The in-

tervals correspond exactly.*'? But remember that the farther from the center the moon's shadow crosses, the briefer its stay on the disk becomes.

193. An eclipse of our moon is an eclipse of the sun for the

moon-dwellers. But from beginning to end a lunar eclipse can last four of our hours plus twenty minutes. On the other hand, the entire moon remains immersed in the earth's umbra two hours and

eight minutes; see my Epitome of Copernican Astronomy,

page

868.3!* Therefore for the moon-dwellers, too, the whole sun can be obscured the same length of time. 194. In the chapter on lunar eclipses in my Optics ?? you have a diagram ?? in which I showed the refraction of the sun's rays in the air surrounding the earth, where the refracted rays enter the boundaries of the shadow on the eastern side, for example, continue through the width of the cone of shadow, and leave on the western side." Therefore, when the moon reaches the western 311. Therefore the section on eclipses in the text of the Dream was already present in the lunar dissertation of 1593. The Rudolphine Tables were originallv

conceived by Tycho Brahe, who preceded Kepler as Imperial Mathematician

to

the emperor Rudolph, and formed part of Kepler's plans for decades before they were finally published in 1627. 312. Kepler, Ephemerides; Frisch, VII, 601 (Oppolzer, Canon of Eclipses, p. 270, Nos. 6740, 6741). 313. Kepler predicted that in 1633 the April eclipse would last 5"52™48°, and the

October eclipse exactly six hours

(Frisch, VII, 601:12

up). But these durations

greatly exceed four hours, and therefore the intervals do not correspond exactly. That is why in the next sentence Kepler reminds his readers that non-central

eclipses don’t last as long as central eclipses. 314. In answer to the question “What is the maximum duration of lunar eclipses, and what is the maximum immersion in total lunar eclipses?” Kepler computed various cases. Among them the longest duration of a lunar eclipse, with both the sun and the moon at apogee, is 4"20"4', and the longest total immersion 2"8™36° (Kepler, Epitome; Gesam. Werke, VII, 494:7-8, 21-22, 32). 315. Kepler refers to Ch. 7, which is entitled “On the Earth’s Shadow.” 316. Kepler's diagram is reproduced in Gesam. Werke, II, 235. 317. The diagram cited in fn. 316, above, illustrates a discussion in which Kepler

declared that “the sphere of the earth is surrounded by a sphere of air, which as a

Kepler's Notes on the Dream

121

boundary of the shadow, it encounters the refracted solar rays coming from the eastern edge of the earth. But these become visual rays. Hence the moon-dwellers think that they see a small eastern part of the sun behind their Volva, when nevertheless practically the entire sun is visible in addition, ahead of Volva on its western °'° side. And this happens to those lunar regions which we see quite red in an eclipse of the moon. For this redness is caused by the refracted rays of the sun.

195. And,

moreover,

unless the moon

is passing through

its

apogee. For observational tests have shown that the refracted rays of the sun cross the shadow lower down and do not reach the moon when it is at its greatest distance from the earth.?!?

196. Undoubtedly there is sometimes present in the very sub-

stance of the rarefied regions a wonderful light which does not come from the sun, either through its primary rays or its secondary

rays.??? Since this happens in the earth’s atmosphere, it can occur in the same way also in the moon's atmosphere. 197. For the earth, or Volva, is illumined also by the full moon, and from that illumination it acquires a certain white light. There-

medium is denser than the ether." Those rays of the sun which would be tangent to the earth if they were not refracted by the atmosphere “strike the earth and are there prevented from going any farther. But the sun lights up the entire sphere of air, as much of it as is presented to the sun. Therefore the sun emits other rays on the outside of [those rays already mentioned]. At least some of these outside rays will be tangent to the sphere of the earth, and [others] will cross over beyond

the earth to the 234:32-235:2). 318.

By

a slip

opposite

of

the

side

pen

of the

Kepler

air"

wrote

(1634 ed., p. 68; Frisch, VIII, 61:1). The

(“western”).

(Kepler,

orientali

Optics;

Gesam.

(“eastern”)

context, however,

in

Werke,

the

II,

Somnium

requires occidentali

319. “The earth’s shadow, as defined by the outermost refracted rays of the sun

which are tangent to the earth, is 43 earth-radii long. When the moon is at its perigee, I have already said, it crosses 11 radii farther on, so that this shadow of the earth would never touch the moon” (Kepler, Optics; Gesam. Werke, II,

242:23-27). Instead of the moon at perigee, as in the Optics, here in Note 195 Kepler puts the moon at apogee, to keep it beyond the range of the apex of the

earth’s shadow. The observations referred to were made by Tycho Werke, IT, 235:3-4).

320. In the Epitome, when

Brahe

(Gesam.

Kepler discusses “that bright substance around the

sun in the ether,” he defines the “secondary ravs of the sun” (radios solis secundarios) as those rays which are “refracted twice in our air circulating around

the earth, once on the wav in, and again on the way out.” Presumably “the rays which are refracted once, on the way in” are Kepler’s primary ravs (Epitome; Gesam. Werke, VII, 496:12-16).

122

Kepler's Notes on tbe Dream

fore, so long as what is prevented from seeing the sun is not the entire moon, but only one of its two edges, that is, the eastern or western part of the divisor circle, Volva does not undergo a complete blackout together with the sun. Volva does indeed blot out the whole sun for that edge of the moon, but by virtue of the white light received from the moon, Volva is in turn visible to those moon-dwellers. These statements have been written in a confused manner, however, and they should be applied, not to any eclipse of Volva, but to its regular disappearance at new Volva, just as the moon vanishes for us at every new moon.

198. Interpret “middle”

here as referring, not to a particular

place on the moon, but to the shadow of the earth.?! For light and imparts none to the the whole sun from the whole

entire time spent by the moon in the at that time the moon itself has no earth or Volva, which then cuts off moon.

199. Also interpret these words as follows. Let total and partial

solar eclipses among the lunarians correspond to total and partial lunar eclipses among the earth-dwellers. In all these cases apply the term "eclipse" to the sun, but to Volva only to this extent: because the sun is eclipsed, the sunlight reflected by the lunar globe to the earth or Volva is likewise interrupted. Thus Volva lacks not only the direct light of the sun on account of the usual new Volva, but also the secondary light of the moon because the sun is eclipsed for the lunarians.

200. The warmth of moonlight

(even though it is barely 1/15

of Volva's light) we may investigate with our sense of touch, aided of course by art. For if you receive the rays of the full moon on a concave parabolic, or even spherical, mirror, at the focal point,

where

the rays come

together,

you

breath,??? as it were. This happened

will feel a certain

to me

at Linz, when

warm

I was

321. In answer to the question "What is the middle of an eclipse?" Kepler re-

plied:

"When

the center

of the

moon

coincides

either

with

the

center

shadow or with the perpendicular drawn from the center of the shadow path of the moon" (Epitome; Gesam. Werke, VII, 492:28-30). 322. The misprint habitum in the Somnium (1634 ed., p. 69)

was

of

the

to the

corrected

to

which

the

halitum by Frisch (VIII, 61:27 up). In saying “This happened to me at Linz,” did Kepler imply that he wrote Note 200 after he left Linz in 1626? Plutarch's

"dark

grape

(Somnium,

Moon

(929A)

referred

is not ripened,"

to that body's

or "dried

out"

"feeble

as Kepler

heat"

by

translated

1634 ed., p. 119; Frisch, VIII, 86:21-20 up). Nevertheless,

well have been the first scientist to report (accidentally)

the

passage

Kepler may

feeling on his own skin

Kepler's Notes on the Dream

123

busy with other mirror experiments and not thinking about the warmth of light. For I began looking around to see whether anybody was blowing on my hand.

No proof is in fact required that this bright light of Volva (that is, of our earth illumined by the sun) belongs to the category of producers of heat. For sometimes in the summer the strength of the sun’s rays is so great that trees and wooden roofs burst into flames,

when the common people subject suspects to charges of arson. What does it matter, then, if the moon is fifty thousand miles away from this heat, when that distance brings into view at one and the same time, as the nearest part of the terrestrial globe, a portion which 1s even greater than a full hemisphere? 201. This is small in itself, yet in the heap of causes perhaps it should not be neglected. For the sun is farther away from the Subvolvans at new Volva by the entire diameter of the lunar orbit than it is from the Privolvans in the middle of their day. 202. [his is a probable conjecture, but there is no complete

proof. Experienced sailors say that the ocean tides are higher when

the luminaries are in syzygy ?? than when they are in quadrature. But the causes of the ocean tides seem to be the bodies of the sun and moon attracting the ocean waters *** by a certain force similar to magnetism. Of course the body of the earth likewise attracts its own waters, an attraction which we call "gravity." What, therefore, prevents us from saying that the earth attracts the lunar waters too, just as the moon attracts the terrestrial waters??? This the warmth of moonlight concentrated at a concave mirror's focus. The term "focus" was introduced into science by Kepler when he was discussing conic sections in his Optics: "On these lines there are some especially noteworthy points which may be defined precisely but have no name, unless you use the definition or some property for a name . . . . In connection with light, with my eyes turned toward

mechanics,

I shall

call

such

a

point

the

focus"

(Gesam.

Werke,

II,

91:11-17). Kepler chose “focus” because it means "fireplace." 323. Kepler's copulis is not restricted to conjunction, for, a few lines below, Kepler speaks of the two bodies being "either in conjunction or in opposition." In answer to the question “What do you designate . . . as the copulas?" Kepler replied that the copulas occur when the two bodies in question are "on the same side or on opposite sides" of a third body, and he then proceeded to distinguish the "more remote copula" (opposition) from the "nearer copula" (conjunction) (Epitome;

Gesam.

Werke,

Vl, 450:1-14).

324. For the importance of this passage in the development of Kepler's concept of gravity, see Appendix H. 325. This question mark, which was inadvertently omitted in the Sommnium (1634 ed., p. 70), was correctly inserted by Frisch (VIII, 61:10 up).

124

Kepler's Notes on the Dream

being granted, if the sun and Volva are either in conjunction or in opposition, their attractive force will be combined. But when the bodies are in conjunction, they remain at the zenith of the Subvolvans for a long time, and do not move away as quickly as do the sun and moon from the zenith of the earth’s ocean. Hence there seemed to be enough time for all the water to be pulled out of one hemisphere into the other. But something is missing from this reasoning. For in order that this transfer may occur, the entire surface of the moon must be accessible to water, and there must be no coasts to act as a hindrance anywhere. Now, however, the telescope has revealed to us mountains, hills, and enormous coasts. Consequently these ramparts, so to speak, must be pierced by valleys and ditches, like very deep clefts, to make it possible for so much water to flow back and forth from one hemisphere to the other. Let us believe this for the time being until some explorer goes into the matter in person.

203. Ihe tops of the mountains are so close together at so great

a height that there is no danger of their being submerged. 204. At that time, moreover, the Privolvans have their midnight, and for them Volva (although it is not visible) 1s together with the sun. If we compare this situation with the nautical observations of the earth-dwellers, they indeed assert the contrary, namely, that the ocean tide 1s just as high at midnight in the absence of the luminaries as at noon in their presence. Therefore in this place, too, my prophesying breaks down, unless you ascribe the nocturnal high tide of our ocean to its rebound from the American coasts. Against them the moon hurls the water which it draws behind it. In turn, the ocean rebounds from the coasts of Europe and Africa in the reverse fluctuation, which the moon restrains with a new control when it returns on the following day. Such dashing against the coasts, occasioning the fluctuation of the water, you must take away from the moon if you wish to deprive the Privolvans of all their water at their midnight.

205. Of course, the ebb and flow of the ocean are said to be al-

most imperceptible in the quadratures, as though a balance were created between the attractions exerted by the sun rising and the moon leaving the meridian, or the other way round. 206. The earth’ s diameter and so also one of its great circles are to the moon’s as 389:100 (Epitome of Copernican Astronomy,

Kepler’s Notes on the Dream

125

page 483).°°° Therefore the moon’s diameter is a little more than

one-fourth of the earth’s.

207. [his detail of the Dream is older than the Dutch ??* tele-

scope. I ascribe it entirely to Mästlin, my teacher in astronomy. It

is a portion of the theses, which I mentioned in Note 2, above, and I repeated it also in my Optics, page 250.??* But it is confirmed in a wonderful way by the use of the telescope and by certain of Galileo’s observations, cited in my Conversation (page 20),?? and by my own observations: peaks rising perpendicularly five miles from the surface begin to be seen from the forty-fifth German mile

on (see my Epitome of Copernican Astronomy, page 23).??? But

now if you leaf through all the reports of ocean voyages, you will hardly find a greater distance from which land is seen. Consequently, no mountain attains a height of more than one long German mile above the surface of the water. See Snel’s Dutch Eratosthenes.*** How many mountains does the moon have? How 326. “If the moon's radius L be taken as 100,000 units . . . 389,085 will show the

size of the earth's radius T in the same units . . . . Thus the radius T of the earth's body will contain the radius L of the moon's body less than four times" (Kepler,

877-78).

Epitome;

Gesam.

Werke,

VII,

281:8-17;

Great

Books,

Vol.

16,

pp.

327. The word actually used by Kepler was "Belgian." But for him, as for his

contemporaries, “Belgian” was interchangeable with “Dutch.” Thus, in his Optics Kepler referred to the Arctic voyage of the Dutch (Hollandorum, Batavorum; Gesam. Werke, II, 128:1-2), whereas in the Conversation he ascribed the same voyage to the Belgians (Belgarum; Gesam. Werke, IV, 304:20).

328. “The moon is correctly said by Plutarch to be such a body as the earth is, uneven and mountainous. Indeed, the mountains are higher in proportion to their globe than are the terrestrial mountains in proportion to the earth" (Gesam. Werke, II, 220:3-6). In Plutarch's Moon,

934F, 935C) and mountainous 329. Addressing

that body

(930D, 935A).

himself to Galileo, Kepler

book is the ingenious and sound

said:

proof on page

was said to be earthy

“The

next

13 of what

item

in your

(922D,

little

I, too, mentioned

casually on page 250 [of my Optics], but failed to demonstrate. The mountains on

the moon are much bigger than those on the earth, not merelv in relation to their globes, as I put it, but absolutely.

In order

to prove

this proposition,

of course,

vour telescope was needed, and your observational skill? (Rosen, Kepler's Conversation, p. 31). 330. In Kepler's table of vertical heights seen from a distance on a tranquil sea,

an object 4,721 paces high (nearly five of our miles) was said to be visible at a distance of fortv-five German miles (Epitome; Gesam. Werke, VII, 35:last line).

111. Willebrordus Snellius (1580-1626), who succeeded his father as professor of mathematics at the University of Leiden, was saluted by Kepler as "the most skillful of today’s geometers" and “the glory of the geometers of our time" (Gesam.

Werke, VY,

18:22-23: IX, 71:15). Snel’s attempts, published

in 1607-8, to

126

Kepler’s Notes on the Dream

high are they? In the dark part of the half-moon, how great a distance separates the terminator from those bright spots which ascend out of the deep shadow into the light of the sun’s rays? See

Galileo's Assayer,??? written against Sarsi?? and his other works generally.9?* I was observing an eclipse of the sun in May, 1612.7?

Through a telescope equipped with a double lens a bundle of rays was directed onto a white screen. On the circumference of the moon's shadow, that is, of the obscuration which the moon's interposition was causing in the sun's brilliance, on this concave circumreconstitute a part of the lost writings of Apollonius, the great ancient Greek geometer, led Kepler to call him also a “Dutch 104:31). More than a century and a half later one from Latin into English by John Lawson as Pergaeus, concerning Determinate Section, as Willebrordus Snellius (London, 1772).

Apollonius" (Gesam. Werke, IX, of Snel’s attempts was translated The Two Books of Apollonius They Have Been Restored by

In his Eratosthenes batavus (Leiden, 1617; Kepler called it “Belgian Eratosthenes”), Snel invoked the ancient Greek geographer’s name because he was making the first effort to measure the size of the earth by means of a chain of triangles, starting from a precisely measured base. In Bk. II, Ch. 17, Snel turned to the question of determining the heights of mountains. Taking sailors’ reports, and applving to them a correction for refraction, Snel concluded (p. 263), at variance with Kepler, that the Peak (El Pico) on Teneriffe in the Canary Islands was much more than 5 3/8 miles high

in height). Shortly before sketch

his death

(actually this volcano is somewhat less than 2 1/3 miles

in

to Johannes van

Meurs!

332. Galileo's Assayer

(Rome,

1626, Snel Athenae

contributed

batavae

a brief autobiographical

(Leiden,

1625)

in which

he re-

ported that in 1600 “when he was in Prague, he became friendly with the famous man, Johannes Kepler" (p. 298, with an engraved portrait of Snel on p. 296). 1623)

did not discuss the number, height, or loca-

tion of the mountains on the moon. The Assayer’s only reference to these subjects

was Galileo's statement:

“I myself maintain that the moon

. . . has a mountainous,

rough, and uneven surface" (Galileo, Opere, VI, 319:34-36; Drake, Discoveries and Opinions of Galileo, p. 263). What makes this particular lapse surprising is that Kepler himself was tangentially drawn into the running controversy of which

the Assayer was one stage. Kepler's participation took the form of an Appendix to his Shieldbearer for Tycho (Frankfurt, 1625; Gesam. Werke, VIII, 413-25). This

Appendix was recently translated into English by Charles D. O’Malley in The Controversy on the Comets of 1618 (Philadelphia: University of Pennsylvania

Press, 1960, pp. 337-55; appears On p. 279).

in this volume,

the passage

just cited

from

the

Assayer

333. Sarsi was the pseudonym used by Galileo’s adversary, Grassi. 334. After his Sidereal Message of 1610, Galileo did not return to the subject of the lunar mountains in his published writings. 335. Ihis solar eclipse of May 3o, 1612 (Oppolzer, Canon of Eclipses, p. 268, No. 6688) was discussed at great length by Kepler in a private letter (Gesam. Werke, XVII, No. 850:97-255; cf. also XVIII, 389:97-101).

Kepler’s Notes on the Dream

127

ference, I say, I saw two very bright protuberances ??9 extending beyond the roundness of the shadow, that is, of the moon, into the

concave region of brilliance. Lest you argue that they were pro-

duced by the lens or by an optical illusion, they remained on the sun’s disk and traveled across it with the motion of the moon, one

preceding the other in leaving. If you want to know the ratio of

their height to the diameter of the moon, it would have been impossible to perceive them unless they equalled at least 1/60 of the diameter. For the bundle of rays was quite small and not much

bigger than a silver coin of the Empire.??* Therefore the moun-

tains on the moon exceeded at least eight miles in height, because the moon’s diameter is about five hundred miles.338

208. Below, in the Appendix,**? you will find a pit which is

perfectly round, just as if it had been made by hand, and which is ten German miles in diameter. In the middle there is a huge curved

cleft. This is how the valley of the Enns, winding through Mt.

Caecius,**° or of the Inn through the Alps, would appear, I think, 336. In a private letter of November

10, 1612, Kepler reported

that he had

ob-

served these two bumps in the solar eclipse of May 30 of that year, and concluded

that they were lunar mountains (Gesam. Werke, XVII, 36:140-44). 337. If Kepler was thinking of a kreuzer, its diameter was about 5/8 of an inch, as measured for me by the staff of the American Numismatic Society, whom it is a

pleasure to thank for their courtesy.

338. In his Note 206 Kepler made the moon’s diameter a little more than onefourth of the earth’s. In the Epitome his answer to the question “Then how large is

the earth’s radius

nowadays

thought

to be?”

was

“about

860”

German

miles

(Gesam. Werke, VII, 40:14-16). Hence the earth’s diameter would be about 1,720 German miles, of which one-fourth would be 430. Thus Kepler’s statement here in Note 207 that the moon’s diameter is about 500 (German) miles is a convenient approximation. His estimate that the lunar mountains exceeded 8 German miles in height (1/60 X 500 = 8 1/3) goes far beyond the calculations accepted today.

339. See Kepler’s Notes on the Geographical Appendix, Note 14, below. 340. What is Mt. Caecius? Is this perhaps intended to be a Latin equivalent of "Kalkgebirge"? In Arnold Mylius’ list of ancient and modern geographical names inserted by Abraham Ortelius in his Theatrum orbis terrarum (Antwerp, 1570,

fol.

dir,

niv),

“Caecius”

is equated

with

"Schóckel"

But

in Wolfgang

Lazius

(1514-65), whose map of Austria was used by Kepler, “Cecii iuga” is equated with

a forest

near

the

Semmering

Pass, which

of Mt. Schóckel (Chorographia Austriae, this was examined for me by my friend, express my warmest thanks). No wonder errors with regard to names" in Lazius XVII, 175:115-16). The Enns River is Ortelius called "Caecius?

is about

thirty

miles

to the northeast

2d ed., Frankfurt and Leipzig, 1730, p. 39; Professor William H. Stahl, to whom I that Kepler complained about the “many and other geographers (Gesam. Werke, at some distance from what Lazius and

128

Kepler's Notes on the Dream

if anybody

looked down on them from the upper ether while the

sun was setting. But that lunar pit is proportionately much deeper

and more frightening. That there may be no dearth of marvels, 1t seems to be linked somewhere by a crossing in lighter shadow, as though it were a bridge. These observations, however, are more recent than the book.?*! So much the more delightful is this antici-

pation of the truth, made years in advance, and vigorous both in

thought and expression. 209. This was not entirely a mere prediction, based on a consideration of the intense heat generated by so long a day, with the

evident

purpose

of making

year?*?

Galileo published

possible

even

habitation

by

living

moonites. I had also appropriate guesses about the lack of density in the body of the moon; these guesses, derived from its motion, were taken up in my Commentaries on Mars??? The following

his Sidereal

Messenger.

He

strength-

ened this idea by very clear observations, which liken the moon with its numerous caverns to a peacock’s tail.?** See my Conversa-

tion with this messenger, page

14.?? The

entire letter which

I

have appended to this Dream, together with its proofs, pertains to this subject. 210. Which no eye has ever seen.*#® Yet in my discussion of

341. These observations in Kepler's Note 208, reporting a valley curving between mountains within a lunar pit, resemble the conclusion drawn by Kepler from his

observation of July 17, 1623 (see Kepler's Notes on the Geographical Appendix, the second observation added to Note 1, xxxiv, below). The date of that observation, however, like the date of publication of Galileo's Assayer (see above, fn. 332), casts only a

little additional light on the chronology

of the Dreazz.

342. In his New Astronomy or Commentaries on Mars (1609) Kepler concluded

that "the body of the moon sistance” to motion imparted

is undoubtedly of low density and offers weak reto it from without (Gesam. Werke, III, 245:23-34).

This conclusion was not reached by Kepler for the first time when he was writing

this part of the New Astronomy, probably in 1605; in that year he “took it up again" (recemsui) from his 1593 theses, which also described the high mountains of the moon, as Kepler tells us in his Note 207. 343. In 1610. 344. Galileo, Opere, III, 65:9-10; Drake, Discoveries and Opinions of Galileo, p.

24.

345. “For my part I concede the possibility of such lunar valleys, carved by rivers from the curving slopes of the mountains. But these spots are so numerous,

vou add, that they make the bright part of the body of the moon resemble a peacock’s tail, divided into various eve-shaped reflecting surfaces" (Rosen, Kepler's Conversation, p. 24).

346. What was true in Kepler’s time is no longer true today. On October 7, 1959, the Privolvan region or far side of the moon, which is invisible from the earth, was photographed for forty minutes by a camera mounted in a Soviet auto-

Kepler’s Notes on the Dream

129

the Privolvans you observe sound reasoning. It is without doubt particularly valid there, in a region marked by the greatest extremes and the most violent alternation of the most terrific heat and

the most freezing cold. 211.

Here is pure reasoning, divorced from any visual evidence.

However, had I then known that the moon has as many sunken

cavities as Galileo’s telescope has revealed, or had I read Plutarch’s

myth

about

Hecate’s

cave,**7 I do believe

that I would

have

asserted my theories with a freer pen. 212. On the moonite land, I mean. I thought that the living crea-

tures resembled the mountains; see my Optical Part of Astronomy, page 250.?** This proportion is applicable not only to their bodies in comparison with our terrestrial bodies but also to their func-

tions, breathing, is demonstrated discussed in the ence of extremes

hunger, thirst, waking, sleep, work, and rest. This by the highly conspicuous size of their works, as Appendix; ??? it is further proved by the persistof heat and cold and by the scarcity of rebirths;

on this subject see Plutarch’s book, page 1730.°°°

213. This is from the Tübingen theses.??! It, too, is intended to

express a proportion, a subject to which I have been most attentive

from an early age. Between the very slow motion of the fixed stars for us and the brief periods of the individual planets down to the

daily rotation of the earth there is a proportion which seemed to

me to be also that of human life to the modest size of our bodies.

matic interplanetary station, which had been rocketed into orbit around the moon.

On the basis of these photographs an Atlas of the Moon’s Far Side was edited by

N. P. Barabashov, A.A. New York: Interscience, 347. Plutarch, Moon, 178-70, or Frisch, VIII, 1595 (see Kepler’s Note

Mikhailov, and Yu. N. Lipsky (tr. Richard B. Rodman, 1961). 944C; Kepler’s translation in the 1634 Sonmmium, pp. 102:17-19. Kepler first encountered Plutarch’s Moon in 2, above), and therefore this portion of the text was writ-

ten by Kepler before 1595. 348. “Among us it happens that men and beasts conform to the tvpe of their region or province. Therefore the creatures living on the moon will have much more massive 220:7-9).

bodies

of a much

tougher

calibre

than

ours”

(Gesam.

Werke,

349. See Kepler’s Notes on the Geographical Appendix, Note 17, below.

350. According

to Plutarch’s

Moon

(939B),

between

its extremes

of heat

If,

and

cold the moon has a temperate season. This suggested to Kepler the possibility of

rebirths, which he discussed in his Note 86 on Plutarch’s Moon (1634 Somnium, p. 162: Frisch, VIII, 118). For the Plutarch edition used by Kepler, see Appendix D. 351. “The Tiibingen theses” in question were Kepler’s lunar dissertation of 1593 (see Appendix C).

130

Kepler’s Notes on tbe Dream

For the moon, on the other hand, the fixed stars return more quickly than Saturn, whereas a day is thirty times longer than ours. Hence I thought that I should attribute a short life to the living creatures but enormous growth, so that nothing would attain a

stable state and everything would perish in the midst of its develop-

ment. In the theses I passed over into politics, supposing that the commonwealth was frequently subject to very great changes but private fortunes were often large.???

214. Since I had deprived the Privolvans of water, and I was

compelled to leave them immense alternations of heat and cold coming directly on each other's heels, it occurred to me that those regions could not be inhabited, at least not out in the open. Hence it was convenient that water flowed in at fixed times of the day. When it receded, I had the living creatures accompany it. To en-

able them to do so quickly, I gave some of them long legs and

others the ability to swim and endure the water, with the proviso that they would not degenerate into fishes. None of this will be unbelievable to anybody who has read about Cola, the Sicilian man352. The omission of these political comments from the Dream shows that when

Kepler expanded his student thesis into the Dream, he did not do so by merely adding further material. When he wrote the thesis in 1593, the political situation

was relatively calm. On the other hand, the Dream opens with a reference to the

quarrel between the Holy Roman Emperor and his brother, a quarrel which resulted a few years later in the abdication of Rudolph II, Kepler’s patron. Under

the circumstances it is not surprising that Kepler decided it was prudent to delete his earlier remarks about “frequent and very great changes” in the commonwealth. In the very great change which occurred when Rudolph II was challenged by his brother Matthias, Kepler as Imperial Mathematician was asked to read the heavens. On Easter Sunday, 1611, he wrote to a highly placed adviser of Rudolph: “I was consulted about the decrees of the stars by persons who are to my knowl-

edge opposed to the emperor. I replied with statements which in my judgment are

not significant in themselves, but may dishearten the gullible; namely, that the emperor is going to have a long life; he shows no indications of misfortune; while there are evil convolutions and eclipses, these occurred one, two, and three years ago. On the other hand, for Matthias there are threatening disturbances . . . . I make these statements to the emperor’s enemies because, even if they are not struck by fear, they are certainly not made confident. I would not make these

same statements to the emperor himself, because in my opinion they are not important enough to rely on. Moreover, I am really afraid that they would make the emperor unreasonably obstinate to the extent of neglecting the ordinary measures which are perhaps available to him through the intercession of loyal nobles”

(Gesam. Werke, XVI, 374:27-38). This psychological warfare was Kepler’s con-

tribution to the party supporting Rudolph against Matthias. But when the latter triumphed not long afterwards, Kepler celebrated the coronation of his new im-

perial patron in a Latin astrological poem (Frisch, VIII, 804-5).

Kepler’s Notes on the Dream

131

fish.333 Moreover I thought that nothing on earth 1s so fierce that God

did not instil resistance to it in a particular species of animals:

in lions, to hunger and the African heat; in camels, to thirst and the vast deserts of Palmyrene north, etc.

Syria; in bears, to the cold of the far

215. On this principle, that all matter, insofar as it is matter lacking a soul, is in itself cold; if it is warmed up by an external cause, by its own nature it returns to its state of cold when the induced

heat passes away, because the cause has ceased to operate. Now

of

course the waters of the Privolvans feel the heat of the sun's rays at

353. Where did Kepler himself read about Cola? In his Note 221 he quotes from Scaliger’s Exoteric Exercises, which in all likelihood was his principal source of

information

(or

rather,

misinformation)

about

Cola.

Julius

Caesar

Scaliger

(1484-1558) in 1557 published an extensive attack on Jerome Cardan's Subtlety (1550). Undoubtedly with the intention of deliberately misleading his readers,

Scaliger entitled his attack The Fifteenth Book of Exoteric Exercises on Jerome Cardan's Subtlety, although

Scaliger never wrote

Books

1-14. In his Exoteric

Ex-

ercises Scaliger began the heading over Exercise 262 with "Cola the Fish," and then started the exercise itself as follows: “The Italian people shorten many names. Many of them say 'Ceco' for Francis, 'Beco' for Dominic, 'Renzo' for Lawrence . . . . In like manner for Nicholas the Sicilians and Calabrians say ‘Cola.’ This name . . . was given to a certain young diver. Why you [Cardan] called him ‘Colanus,’ I do not know.” Then Scaliger proceeded to talk about “those who for

some reason remain under water for a long time." Besides calling him "Colanus," Cardan had further said that he was “a diver and resident of Catania, which is a

city in Sicily. It is well known that he lived a little before our time, or rather in

our time. He used to hide under the water for three or four hours, like a fish" (De subtilitate, ed. Basel, 1560, 8°, pp. 810-11). This particular edition of Cardan’s Subtlety, rather than any other of the very numerous issues, is cited here because an ingenious demonstration has established that Kepler used the Basel, 1560, octavo edition (Gesam. Werke, XIII, 408). In his Optics Kepler discussed a passage of the Subtlety at great length (Gesam. Werke, II, 28-29), and he cited the work also in his New Astronomy (Gesam. Werke, III, 284:23-24) and in his Harmonics (Gesam. Werke, VI, 48:20, 49:1). In Kepler’s judgment, Cardan (1501-76) belonged with the “most outstanding philosophers of this age" (Gesam. Werke, II, 120:9-10). As for Cardan’s critic, Kepler

said: "When I entered upon the study of philosophy at the age of 18 in 1589, the young fellows were busy with Julius Caesar Scaliger’s Exoteric Exercises. Stimu-

lated by this book, I began to develop various ideas in succession on various problems such as the heavens, souls, spirits, elements, the nature of fire, the origin of springs, the ebb and flow of the sea, the shape of the continents and of the oceans lying between them, and similar questions” (Gesam. Werke, VIII, 15:5-10). With misplaced confidence in Cardan and Scaliger, Kepler, too, believed that Cola (or Colanus) was really a man. The credulity of both his sources prevented

him from realizing that he was dealing with a hoary legend. This has been exam-

ined in detail by Giuseppe Pitré, Studi di leggende popolari in Sicilia, in Biblioteca delle tradizioni popolari siciliane, Vol. 22 (Turin and Palermo, 1904), pp. 1-173.

132

Kepler's Notes on the Dream

the surface; but those rays do not penetrate to the lower layers, on account of the depth, I believe. 216. Surely everything was destined for a definite use. But the heat of the water followed from the great length of their day, and from the experience of the Chilean region at the Tropic of Caprıcorn and in the torrid zone even with our short day. For according to the writers, the rain comes down quite warm."

217. This is, so to speak, their occupation. For should anybody

object that those regions are uninhabitable if the water, too, is very hot, I send him down to our cellars and deep wells, in which we keep our drinks cool in the summertime. 218. The precedents were our vegetables’ and fruits’ rinds, vary-

ing with nature’s varying providence; the precedents were oysters’ and turtles’ shells, shaped like shields; the precedents calluses on the feet, the hoofs and soles of animals.

were

the

219. I had read in Arnobius the African ®°® that among the pleasures of his people it was an accepted practice to expose them-

selves naked to the sun, basking like lizards and, unless I am mis354. In

his

Note

222

Kepler

cites

José

de

Acosta

(1540-1600).

Presumably,

therefore, here in Note 216 he has in mind Acosta’s statement in the same passage

that in the “torrid zone . . . the rains . . . come down warm" (The Nature of the New World, Bk. 2, Ch. 10). Acosta published this work (De natura novi orbis, Salamanca, 1588) together with a treatise On tbe Promulgation of the Gospel among the Barbarians or On Procuring the Salvation of the Indians (De promulgatione evangelii apud barbaros sive de procuranda Indorum salute). A long pas-

sage of this second

treatise was

quoted

by

Kepler

in his New

Star

(Gesam.

Werke, I, 350:1-26). When Kepler echoed the words De procuranda Indorum salute, he was citing Acosta's treatise by the short title used by Acosta himself.

The passage quoted by Kepler occurs in Bk. 5, Chs. 9-11, of Acosta's treatise Oz

Procuring tbe Salvation of tbe Indians. 'The two-book version of Acosta's Nature of the New World, together with his Salvation of tbe Indians, was reprinted at

Koln in 1596. If this was the edition used by Kepler, he found the rains coming

down warm on p. 84, and the Indians being idolatrous on pp. 468-83. When Kepler told Fabricius that little could be learned from Acosta's treatment of atmospheric conditions in general (Gesam. Werke, XV, 126:449, 26811142), he may have

been referring to Bk. 2, Chs. 12-16, of the Nature of the New World (ed. 1596, pp. 88-98). The latter treatise, expanded into seven books entitled Natural and Moral History of tbe Indies, was translated into English by Edward Grimstone (London, 1604; reprinted by the Hakluyt Society, No. 60-61, London, 1880). 355. The Arnobius who wrote Against the Pagans about 300 A.D. is surnamed

“the African” in order to distinguish him from a later Christian author of the same name, who is called Arnobius “the Younger." Arnobius “the Elder” or “the A frican” was translated into English by George E. McCracken in Ancient Christian Writers, No.

7 (Westminster, Maryland:

Newman,

1949).

Kepler's Notes on the Dream

133

taken,??* also like crocodiles. The nature of the latter as beasts of the country is taken on by the Africans, I supposed, on the basis of this similar practice." For it would surely be rather a sort of torture for us Europeans. 220. About the people of Lucumoria,??? a province of Scythia in the far north, it is written that some of them die when they are assailed by that long night, and revive when the sun returns;??? hence they seek out safe coffins, lest anything bad happen to them during the absence of their soul. See Martin del Rio's discussion of

these people in his Investigations of Magic.?9?

221. From the resin which exudes from ship timbers as a result of the sun's heat and sticks together in a ball, ducks are born. The

356. Kepler is mistaken. Evidently he is trying to quote from memory, has given free play to his lively imagination. Arnobius actually said: "If accustomed to baking himself in the sun and dehumidifying his body . . plains that very thick clouds take away the pleasure of a clear day, shall we fore say that the clouds hang out an unfriendly cover, because they do not the acquisition of a suntan in comfort and at will?"

and he anyone . comtherepermit

(Against the Pagans, Bk. I, Ch.

9). Arnobius did not say that nude sun-bathing was an accepted practice of his people.

357. In a private letter dated January 17, 1605, Kepler remarked with equally mistaken assurance that "according to Arnobius, Africans are akin to reptiles in nature" (Gesam. Werke, XV, 110:343-44). He was talking about reptiles in con-

nection with his thesis that light is associated with heat. "Do you really deny,” he asked his correspondent, "that the sun's rays heat things up? Do you therefore

think that snakes and crocodiles

(Africans are akin to reptiles in nature, according

to Arnobius) bask in the sun only for show?" The last word has been translated as

though it were spectacula, although specula is printed in Gesam. Werke, in agreement with Hansch, Epistolae, p. 234. But specula is surely out of place in this con-

text. The Austrian National

Library

in Vienna

possesses

a manuscript

(Codex

10703), which, at pp. 269-74, contains this letter, the earlier part of it copied by a

secretary, and specula appears was finished by scrutinize what

the rest of it in Kepler's own handwriting. The false reading on p. 272 in the portion copied by the scribe. What he left undone Kepler himself, who may not have taken the time and trouble to his amanuensis had written.

358. This is the reading in Somnium,

1634 ed., p. 74. It was changed

to “Culo-

moria" by Frisch (VIII, 63:2 up), presumably in order to bring it closer to the form “Cucomoria,” used earlier by Kepler (Gesam. Werke, IV, 201:18). But Kep-

ler's source used the form “Lucomoria” (see Appendix M, below). 359. The resurrection of these northerners after their long winter

night

is as

fabulous as the return of Kepler's flies to life in the daytime after dying at night.

Is it possible that Kepler somehow further muddled the already muddled account in Pliny’s Natural History, xi.36 (43)? After mentioning a "flying creature" which

“lives no more than one day,” Pliny savs that “flies which have died in water are restored to life if thev are buried in ashes." 360. See Appendix M.

134

Kepler's Notes on the Dream

last part of their whole body to develop is the bill. When this 1s released, they slip into the water below. So says Scaliger in his Exercises.2°! The Scottish tree which produces the same offspring is well known because many people have made it famous??? In the year 1615, when the summer was very dry, at Linz I saw a juniper

twig that had been brought in from the abandoned fields of the Traun. The twig had given birth to an insect of unfamiliar shape and of the color of a horned beetle. The insect had emerged up to its middle and moved slowly. The back parts clinging to the tree were juniper resin.?9? 361. “In the British Ocean you would marvel more at a bird unknown to you. It has the face of a duck. By its beak it hangs from the rotten remains of wrecked ships until it is detached and goes away to look for fish, off which it feeds. This too has been seen by me” (Julius Caesar Scaliger, Exoteric Exercises, Exercise 59, Pr. 2). 362. “We found many eggs of the barnacles (which the Dutch call Rotgansen) and the barnacles themselves sitting on eggs in their nests. When they were driven away,

they

cried

‘Rot,

Rot,

Rot’

(the

call

from

which

they

get

their

name).

By throwing a stone, we killed one. We cooked and ate it, together with about sixty eggs, which we had taken back to the ship. “These geese, or barnacles, were

the true geese, called Rotgansen,

which

come

every year in large numbers to the vicinity of Wieringen in Holland and are caught. Heretofore it has not been known where they laid their eggs and raised their young. This is the reason why some authors have not been afraid to write that in Scotland the barnacles are born on trees whose branches grow out over water;

if the fruit drops into the water, goslings

known

where

are born

which

swim

at once,

but if the fruit falls on the ground, it rots and does not develop. The falsity of these statements is now clear. It is not surprising that heretofore it has not been these birds lay their eggs, since nobody

(so far as has been ascer-

tained) ever went up to 80°, nor was this region ever known in that locality, much

less those geese incubating their eggs” (Gerrit de Veer, Nautical Diary, Amsterdam, 1598, fol. ısr). Kepler studied this brief book carefully (see above, fnn. 22

and 243). He could therefore scarcely have overlooked the quoted passage, which was emphasized by the following sidenote: “Barnacles lay their eggs and raise their young in Greenland at a latitude of 80°.” Nevertheless, he chose to repeat the medieval legend of the barnacle goose, and to ignore the historic refutation of it which he had before him in De Veer’s Diary. 363. The biological conception implicitly assumed here was stated explicitly in Giovanni Battista della Porta’s Natural Magic: “In our daily experience we

see that many animals can be generated from the bosom of the earth and from decaying

matter.

... Animals

have

this

characteristic

in

common

since

some

with

plants,

that some of them arise from seed, whereas others are brought forth by Nature spontaneously

without

any

antecedent

kindred

seed,

of them

come

from the ground or from rotting vegetation, like insects, and others from the dew that settles on leaves, like caterpillars” (Bk. 2, Chs. 1-2). Kepler told Herwart von Hohenburg

that “Porta’s Magic

was published

at Frankfurt

in the year ’97”

(Gesam. Werke, XIV, 345:136). Kepler studied this book diligently, and quoted it

Kepler's Notes on the Dream

135

222. The same statement is made by José de Acosta about regions in the New World?** See my Conversation with tbe Sidereal Messenger, page 18.995 223. I derived this conjecture from a disputation presided over by Mastlin and published in the year 1606 °° under the title The Phenomena of tbe Planets.**" I discuss the conjecture also in my frequently. Its numerous editions and translations, as well as Della Porta’s incon-

sistent statements about his own career, were discussed by Edward Rosen in The Naming of the Telescope (New York: Abelard-Schuman, 1947), pp. 6-30. The anonymous English translation of Della Porta’s Natural Magic (London, 1658) was reissued almost exactly three centuries later by Basic Books (New York, 1957). 364. “Hence the heat of the burning sun is intercepted by the clouds, and the rains which drop down from them moisten and cool the air and the earth at the same time" (Acosta, The Nature of the New World, Bk. 2, Ch. 10; ed. Kóln, 1596, pp. 83-84). In Bk. 2, Ch. 11 (ed. Koln, 1596, p. 87), Acosta said: “The great depth of the ocean prevents the water from being affected by the sun’s heat, as river water usually is throughout.” This looks like the statement Kepler had in mind when, in the text of the Dream (p. 28, above), he remarked: “For in those very deep layers of the water, they say, the cold persists while the waves on top are heated up by the sun.” 365. “I certainly do not understand how those inhabitants of the moon can bear the sun’s terrific heat at full moon, which we see when it is high noon for them (and the same holds true for the others on the invisible hemisphere at new moon),

unless the dense air covers the sun for them frequently, as happens among

the

Peruvians, and moderates the heat with its moisture” (Rosen, Kepler’s Conversation, p. 29). 366. Here in Note 223 on the Dreamz Kepler gives the date 1605 for this disputation. In 1627 he made the same error in a letter to Schickard (Gesam. Werke, XVIII, 322:31-34) when relating that he had been asked to procure a copy of the

disputation for an Italian mathematician who had been recommended

Galileo

(Gesam.

Werke,

XVIII,

No.

1054; Galileo, Opere,

XIII, No.

to him by

1836). The

Italian wanted to buy a copy "whatever the price." His offer was passed along by

Kepler to Schickard in Tübingen, where the disputation had been printed more than two decades before, with the request: "Write me . . . whether it survives,

and send [me a copy] if you can get hold of one." Evidently the disputation was already a scarce item. In earlier references to it Kepler had dated it correctly in 1606

(Frisch, III, 533:6 up; Gesam.

Werke,

IV, 300:8, 311:12). But in 1628 Kepler

admitted: "I am losing my memory" (Gesam. Werke, XVIII, 330:8). 367. Here Kepler gives the title of Mästlin’s disputation as De

planetarum.

In this context

passionibus

is a technical

astronomical

passionibus

term.

In the

Epitome Kepler printed a "Synoptic Table of the Various Passiones of the Planets"

(Gesam. Werke, VII, 468). These passiones include velocity, acceleration, direction of motion, brightness, phases, spots, conjunctions, eclipses, occultations, etc. Kepler

explained that "in the case of the planets the word passio is the Latin translation of the Greek 'pathos, which is a little more appropriate. For astrology pretends that the planets are themselves really affected by all those things which observa-

tion imagines

In any

concerning

case, De

them"

(ibid., 469:7-9).

passionibus planetarum

was

merely

Kepler's

short title for

136

Kepler’s Notes on the Dream

Conversation,

page

19.°°8 Nevertheless,

the topic is worthy

of

being treated here, too, in its entirety, because of its relevance. Let

us therefore go into it a bit. As I was saying, in his Theses 136 and 143 the author begins to deal??? with the following phenome-

non.3”° Sometimes the moon is visible on the same day both in the morning as the old moon, and in the evening as the new moon,

when it can be no more than 6? or 7? away from the sun. Yet at other times

12°

are required

for its reappearance.""!

To

explain

the causes of the phenomenon, in Thesis 146 he proposes a new

theory, to the effect that the moon is surrounded by a certain airy

substance. For in Thesis 139 he had proved that when the moon

has moved twelve whole degrees away from the sun, hardly 1/80 *** Masdin's Disputatio irregularitatibus, seu

de multifariis motuum planetarum in regularibus inaequalitatibus, earumque

coelo causis.

apparentibus astromomücis

( Tübingen, 1606). A copy of this rare work was once available to Frisch (Frisch,

II, 418:12 up, 498:14) and to Franz Hammer, when he edited Kepler's Conversation (Gesam. Werke, IV, 509). But at the present time the editors of Gesarn. Werke can no longer lay their hands on a copy of Mästlin’s Disputation about the Manifold Apparent Non-uniformities, or Uniform Inequalities, in the Motions of the Planets in the Heavens, and the Astronomical Causes of the Inequalities. 368. Page 18 would have been a more accurate citation (Rosen, Kepler’s Conversation, p. 29). 369. The misprint aegere in the Somnium (1634 ed., p. 75) was corrected to agere by

Frisch

(VIII,

64:16).

370. Here Kepler uses the Greek term “pathos” (see above, fn. 367). 371. Ihe moon moves about 12° eastward away from the sun every day. In his

New Star Kepler asked: "Doesn't the doctrine of the ancients require two days and more after conjunction for the first visibility of the moon?" (Gesam. Werke, I, 266:32-34). After an extended discussion of the subject in his Optics, Kepler had aligned himself with those who maintained that under exceptional circumstances the full and new moon could be seen on the same day (Gesam. Werke, II, 226:8-12; see below, fn. 389). In his Epitozze he still adhered to this mistaken notion (Gesam. Werke, VII, 478:19-21). In his Discourse on the Great Conjunction Kepler said with regard to the future lunar eclipse of April 14, 1623 (Oppolzer, Canon of Eclipses, p. 368, No. 4370): “If anyone stands on a high place and has an unobstructed horizon, he [Frisch’s per should be der] will be able to see both sun and moon at the same time

as a result of refraction. This is regarded by astronomers as a delightful spectacle” (Frisch, VII, 691:20-22). 14-16), with reference to clear sky, I went out to might happen to see both

Then, in his Epbemerides Kepler recalled (fol. Bbzv: this same eclipse, “When the evening seemed to promise a the mountain overlooking Linz, thinking that perhaps I sun and moon at the same time as a result of refraction,

because the moon while still in eclipse was in the process of setting" (Frisch, VII,

$36:21-18 up).

372. In the Optics Kepler put the visible portion of the moon's

when its distance from the sun was 5? (Gesam. Werke, II, 225:37-39).

disk at 1/70

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Matthias Bernegger, Kepler's friend

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Kepler's Notes on the Dream

137

of its visible diameter is illumined by the sun at that time. How much smaller, then, will that illuminated portion be if the moon is

no more than 7° away from the sun? Hence, he concludes, all the

air which extends beyond the edge of the moon’s body is colored by the sun’s rays since they can pass through it, that is, it is trans-

parent. Consequently the moon never disappears completely, not even at the time of a central conjunction. He supports this theory by five additional arguments.* In the first place, when a ray

from the eclipsed sun is admitted through an aperture,?** it always makes the outer convex circumference in the image of the sun bigger than the inner concave circumference, namely, of the dark

region cut off or covered by the convex body of the moon. Yet the

full moon generally has a bigger diameter than the sun. Accordingly, he thinks, when we measure the full moon, we are measuring that part of the illuminated lunar air which protrudes beyond the body and around it. But when the moon covers the sun, it does so by itself without any help from its aerial tunic, through which the sun’s rays pass without any obstruction or interference. This argument, derived from an observation of a solar eclipse,*”° 373. Ihe term used here by Kepler is experimentis, which occurs ten times in his Note 223. Once it means “experiment,” once “phenomenon,” and the other

eight times “argument.” In this last sense Kepler employs documentum four times as the equivalent of experimentum. 374. In his Optics Kepler described how

he helped

Mastlin perform

this experi-

ment; he also supplied a diagram, and pointed out the defects in the procedure (Gesam.

Werke,

II, 300-301).

375. According to Günther

(Traum, p. 146), this is the eclipse of February 25,

1599 (Oppolzer, Canon of Eclipses, p. 268, No. 6659). But this eclipse was discussed in a letter which Brahe wrote to Mästlin on April 21, 1598 (T'ycbonis Brahe... opera, VIII, 55:37; Mastlin’s erroneous date, April 25, was corrected in Gesam.

Werke, XIII, 280:271; 411). In view of the letter's date, Brahe's reference to “the eclipses which occurred in the February just elapsed" (Tychonis Brahe . . . op-

era, VIII, 54:26) left no room for doubt that February, 1598, was intended. But long before Günther our eclipse was mistakenly postponed to :599. In a

letter to Kepler on December 9 of that year Brahe wrote:

"When

I reread the

copy of my letter to Mastlin, I see that in it I mentioned the solar eclipse which occurred on February 25, ’98.” By a scribal error the year was written as “’99”

(Tychonis Brabe . . . opera, VIII, 210:12)

the editors (bid., 434, 441). The passage in the letter of Brahe

and had to be corrected to “’98” by

to Mastlin

referring

to "the eclipses

which

occurred in the February just elapsed" was extracted by Mastlin and transmitted

by

him

to Kepler

in a communication

dated

January

12,

1599

(Gesam.

Werke,

XIII, 279-80). Kepler, in turn, recopied the extract for Herwart von Hohenburg three months

later. By that time,

however,

there could

be a real question

which

138

Kepler's Notes on the Dream

is indeed entirely correct. It persuaded Tycho Brahe, too, to declare that the diameter of the new moon is less than the diameter

of the full moon.?'? Longberg in his Danish Astronomy

likewise

February was meant in the reference to “the eclipses which occurred in the February just elapsed,” and therefore a clarifying marginal note “year '98" was felt to be necessary (ibid., 322:723). Our unfortunate eclipse was affected by another blunder, which was left uncorrected in Tychonis Brahe . . . opera. In Brahe's Treasury of Observations “the great solar eclipse” of 1598 is assigned to February 24 (Tychonis Brahe . . . opera, XIII, 117:1; cf. V, 183:5). But in 1598 there was no eclipse of the sun on February 24, as is shown by Brahe’s observation of the sun on that day (ibid., 116:last entry). Moreover, Brahe's Treasury of Observations includes reports from Longberg, Fabricius, and a third correspondent, all of whom dated the eclipse on February 25 (ibid., 119, 120, 154). In fact, Brahe himself in his aforementioned letters to Mästlin and Kepler pinpoints the day as February 25 (ibid., 54:26 and 35, 210:12; Gesam. Werke, XIII, No. 110:224, 233; No. 117:722, 732; XIV, 96:269). These observers, working in areas opposed to the introduction of the Gregorian calendar (new style), used mainly the Julian calendar (old style), in which February 25, 1598, was the Gregorian March 7, 1598. Hence in Oppolzer, Canon of Eclipses, p. 268, our eclipse is No. 6656 (not No. 6659). “In the year 1598, March 7 (new style) and February 25 (old style)" our eclipse was observed by Kepler at Graz (Frisch, VIII, 15:7), and at the end of his Calendar for the Year . . . 1599 he announced that he had written “a special report" on it (ibid., I, 408:7 up). But in a letter to Mastlin on December 8, 1598 he admitted: "I indulged in great immodesty . .. . Do I make a bold promise that I can exhibit

a whole treatise on the eclipse? But what sort of treatise? There is none yet, to tell the truth . . . . At once, before the month

of March

was over, I wrote about

three pages . . . in a popular style, without computations . . . . I added a descrip-

tion of my observation XIII, 252:99-109).

. . . . But nobody has seen what I wrote"

(Gesam.

Werke,

376. In his letter of April 21, 1598, to Mastlin, Brahe wrote that “the new moon in eclipses does not appear to be of the same size as at other times when it is full, although it is equally distant from the earth. On the contrary it shrinks by about one-fifth, for certain reasons to be disclosed elsewhere. As a result the moon can

never cover the entire sun completely, even if visually it is interposed centrally. It is still surrounded by some remaining sunlight, which could be observed also in this most recent eclipse [of the sun on February 25, 1598, old style] by those to whom the maximum obscuration was visible. In the form of crescents on both sides of the moon's body, the sun at that time must have included more than was

demanded by a line drawn through the [moon's] diameter. According to my calcu-

lations, too, the diameter of the moon was 34%’ then. Yet in front of the sun it could not have appeared to be more than 28'. I recognized this constriction, which nobody has noticed before me. But in some observations of the sun, when it was

covered by both the upper and the lower part [of the moon], I learned this phenomenon by experience" (Tychonis Werke, XIII, 280:250-63, 323:749-62).

Brahe...

opera,

VIII,

55:9-22;

Gesam.

Brahe discussed this phenomenon again, in connection with the same eclipse of

the sun, Rudolph

in a work which he presented in manuscript to his imperial patron, II, in 1599. In this work, entitled Prolegomena to the Reestablished Mo-

Kepler's Notes on tbe Dream

139

upholds his teacher.?'* This nightshirt of the moon was discussed tions of the Sun and Moon

(In solis et lunae motus restitutos . . . prolegomena),

which was not printed until 1923, Brahe said that "in this eclipse there appeared something strange which, so far as I know, was not previously noticed by my predecessors (vet I detected it in earlier solar eclipses, and inserted this relationship in my tables). When the moon is new and is observed to be in conjunction with the sun, it certainly does not have the apparent size which it usually has at other times, when it is full and equally distant from the earth. It lacks about onefourth, so that it can never cover the entire sun. On the contrary, the sun extends

slightly

all around

the

body

of the

moon”

(Tychonis

183:18-25; see also II, 148:cols. 5-8 in the table). In his Preliminary Exercises of the Renovated stauratae progymnasmata), Pt. 1, Brahe declared:

Brahe ... opera,

V,

Astronomy (Astronomiae in“When a conjunction of the

luminaries results in an eclipse, it has been observed that the moon does not retain the same apparent diameter as it has at other times. On the contrary, its boundaries are so reduced by the strength of the sun's light, with some optical cause producing this result, that about one-fifth of the moon disappears in this way and does not present itself to the eye. Therefore I have concluded that the apparent diameter of the moon must vary somewhat in conjunctions resulting in eclipses" (Tychonis

Brahe

. . . opera, ll, 147:4-9).

The printing of the Preliminary Exercises was not completed at the time Brahe's death, and the task of superintending the volume devolved on Kepler. his own Optics Kepler reported: “Tycho Brahe noticed that . . . eclipses of sun . . . always showed the moon’s diameter much smaller than it appeared in

of In the op-

positions. At first he thought of an idea, which in the end he defended as a correct statement, and proclaimed publicly in his Preliminary Exercises, Part 1: in

conjunctions the moon does not retain the same apparent diameter as it has in oppositions; on the contrary, its boundaries are reduced by the strength of the sun's

light, with some optical cause producing this result” (Gesaz:. Werke, II, 248:7-14; cf. II, 48:20-23). These closing words must have escaped the attention of Franz Hammer, who edited Kepler's Optics in Gesam. Werke. For Hammer wrote that

“Tycho Brahe regarded as real the apparent phenomenon [of the lunar diameter seeming to be smaller in solar eclipses than at full moon]. He associated therewith the seemingly curious theorv that the moon pulsates in the period of its synodic revolution" (II, 399). But both Brahe and Kepler made it perfectly plain that Brahe's explanation did not assume a physical expansion and contraction of the moon's volume. On

the contrary, Brahe emphasized

that the cause was optical, as

modern astronomers still do in attributing this effect to irradiation. Kepler disputed Brahe's priority in making this discovery. For in his annotations on the

extract from the letter of Brahe to Mastlin, Kepler remarked: “Mastlin wrote me that he, too, noticed the same phenomenon long ago, not merely in eclipses but also when the moon occulted a star" (Tychonis Brabe ... opera, VIII, 434; Gesam. Werke, XIII, 324:781-83). Modern astronomers put the greatest possible

excess of the moon's apparent diameter over the sun's at about 2%’, an order of magnitude in fair agreement with the measurements accepted by Mastlin and Kepler. 377. "When the full moon is in the presence of the earth's shadow, it always shows a somewhat larger radius, in our observation . . . . When the new moon produces an eclipse, the moon's radius diminishes, but it expands in the full moon"

140

Kepler’s Notes on the Dream

at length, also, by the Frisian astronomer, David Fabricius,?** whose opinions I publicized in the introduction to my Ephemertdes. It is entirely correct, I repeat, that when the image of the eclipsed sun is introduced through a small hole, the convex circumference is a part of a bigger circle, whereas the concave circumference is a part of a smaller circle. But the reason advanced by the disputant is not satisfactory. It is not my intention to deny that

there is air on the moon. I accepted it in my Optics, pages 252 °™" and

302,??' as well as in my

Conversation,

page

18.7? Neverthe-

(Christianus Severini Longomontanus [Longberg], Astronomia Danica, Pt. 2, Bk. 1, Ch. 9; 2d ed., Amsterdam, 1640, pp. 297, 300). 378. See Appendix K. 379. In the "Principles by which the Motions of the Sun and Moon are Com-

puted in these Epbernerides" Kepler referred “to Fabricius’ speculation, which he

published in his Prognostication for the year 1616, and to his assertion that there is transparent air on the moon" (Ephemerides, p. 9:12-11 up; Frisch VII, 489, Sec. 27:5-7). The effects which Fabricius attributed to his lunar atmosphere were de-

nied by Kepler. Then, dressed

the Frisian

in reply to Fabricius’

astronomer

directly:

“You

public interpellations, Kepler say

that

on

March

4,

ad-

1607,

vou

of the moon there seemed to intervene less than the bright part. But the moon

was

observed the body of the moon come close to the [star known as the] Bull’s Eve. You saw that while the star was not yet occulted, between it and the bright part not yet fully 90° away from the sun. Therefore the bright part [of the moon] ought still to have been actually smaller than the dark part. Hence you conclude

that the moon’s

globe is surrounded

by a broader sphere

of air. This sphere, by

absorbing sunlight, shows itself to us in place of the true body of the moon. That part [of the sphere], however, which is outside the sun’s rays makes no impression on our eyes. On the contrary, it is transparent and does not prevent us from seeing the stars, even when

it is aligned with

them. You

support

this conclusion

by an

examination of the crescent moon. For the circle with the bright crescent appears

appreciably bigger than the circle of [that part of] the body which is not in the light, though it is visible at the same time” (Ephemerides, p. 21:6-13; Frisch, II, 112:24-33). Kepler proposed “to deduce these and other similar phenomena from the condi-

tions of vision, and to remove them from the heavens and visible objects . . . . By the

ineluctable

rigor

of logic

it follows

from

that

process

of vision

that

such

effects occur in the eye, and that the images of bright objects appear expanded, even though there is nothing like this expansion in the visible object itself . . . . If causes accounting for very many phenomena are present inside the eye, why do you go up into the sky and wrap a shirt around the moon?" (Ephemerides, p. 21:27-36; Frisch, II, 112:3 up-113:10). 380. “Ihe entire moon, as will be stated below, is surrounded by a certain aerial substance” (Optics, Ch. 6, Sec. 9; Gesam. Werke, lI, 221:15-16). 381. "In Chapter 6, Section 9, above, I went so far in the direction of audacity, together with Plutarch, that I dared to ascribe to the moon continents, seas, mountains, and valleys such as our earth has. How much farther [must I go] in order to envelop the moon in air such as surrounds our earth?" (Optics, Ch. 8, Sec. 3; Gesam. Werke, II, 261:28-32).

382. In the Conversation Kepler cited the two passages in his Optics which were

Kepler's Notes on the Dream

141

less, it does not accomplish the result sought by the disputant. For

the phenomenon has a different explanation, namely, the radius of the aperture through which the sun’s ray enters. A bright fringe as wide as this radius attaches itself all around the sickle-shaped image of the sun, including the cusps of the horns, with the result that

they become blunted. When

this bright fringe has been cleared

away, what remains is a pure image, whose outer circumference now 1s narrower, whereas the inner, concave circumference is broader.*** Thus, if this remedy is employed, the diameter of the moon when it covers the sun is found to match the diameter of

the full moon. This is my solution of the problem. From my Optics, which was In print at that time,*** my

solution is quoted

by the man

who

acted as the respondent.?*? In a note to Thesis [146] he cites and quoted in fnn. 380 and 381, above. Then

above, and continued:

he added the remarks quoted in fn. 365,

“At full moon this air hides the spots to a greater degree

and, absorbing an intense brilliance from the sun, reflects it to us” (Rosen, Kepler's Conversation, p. 29). 383. The inner, concave circumference is broader and the outer circumference is narrower than they were before the bright fringe was removed. The contraction of the outer circumference and the expansion of the inner circumference, however, still leave the outer circumference outside the inner circumference, so that the outer circumference remains larger than the inner circumference. 384. Kepler’s Optics was published in 1604, and Mastlin’s Phenomena of the

Planets was printed in 1606 (see above, fn. 366). 385. In his Singular Phenomenon

Kepler said: “Two

years after the publication

of my Optics there appeared a disputation on the irregularities of the heavenly

motions, which was presided over by Michael Mastlin, professor of mathematics at

Tubingen,

while the respondent was Samuel

Hafenreffer"

(Gesam.

Werke,

IV,

83:23-25). The title page of the disputation announced that “while Michael Mastlin presides . . . on February 21 and 22... Samuel Hafenreffer of Herrenberg will attempt to defend” the theses propounded in the disputation (Gesam. Werke, IV, 489; XV, 541).

Hafenreffer received a bachelor’s degree at Tübingen University in 1601 and a

master’s degree three years later (Matrikeln

. . . Tübingen, I, 759). Then

he took

a trip to Austria, where he tutored a nobleman for a year. Giving up this job, he

asked Kepler on January

18, 1606, for help in establishing a connection

with some

other aristocrat at Prague (Gesam. Werke, XV, No. 370). Evidently nothing came of this appeal, since only a little over a month later, on February 21 and 22,

Hafenreffer took part with Mastlin in the public disputation, When it was printed, he sent Kepler a copy on October 4, 1606, with the following explanation:

“Some time ago, when I approached

Professor Mastlin for the purpose of con-

ferring with him, I came across these present theses in his possession. He had written them for his son. I respectfully asked him to hand them over to me so that I

could read them. Granting my request, he added a few remarks about the delightfulness of the subject. While diligently reading them and thinking about them, I was stirred so strongly that I persistently asked him to turn them

over to me as

142

Kepler's Notes on the Dream

accepts my denial of a difference between the new moon and the full moon. Nevertheless, he did not eliminate this first argument from the group of arguments for air on the moon because, I suppose, he felt that the reader should be permitted to decide for him-

self. Or fine an enough? between

did he keep it because he thinks that he used so extremely aperture that even the image’s horns were made sharp I, for one, do not believe him. For there is a big difference the ratio of the diameters which the author adduces from

an observation of the solar eclipse on October

2/12,

1605,°°° and

the ratio which I find in similar observations. Observers should therefore be warned that the paper which receives the image of the eclipsed sun must be protected from all disturbances and must always be placed at the same distance from the hole and at right angles to the ray coming through it. For if the paper bends, the circumferences of the bright image are distorted, and degenerate from

circles into ellipses. Accordingly let the disputant verify whether he took adequate precaution against this defect.

the topic of a public disputation. In this matter, too, he did not fail me, and they were sent to the printer. While they were in press, Professor Mastlin became

seriously ill and could not perform the painstaking work of correcting the proofs carefully. Therefore typographical errors crept in, which you will be able to rectify. I humbly submit to you a copy of these theses, which I ask you to receive in a spirit of good will”

(ibid., 354:14-27). In that spirit Kepler replied on

November 16, 1606, saying: "On the strength of your assurance in your preface, I divide the theses equally between you and Mastlin” (ibid., 359:12-13). Although Hafenreffer continued to be interested in astronomy throughout his life, he made medicine his principal occupation. Earning a medical degree at Tübingen University in 1614, he engaged in private practice. But in 1648 he was designated professor of medicine at Tübingen, where he served as dean of the

medical faculty for the first time in the following year (Matrikeln . . . Tübingen, I, 759; II, 234). He died at the age of 73 on September 26, 1660, according to a contemporary, who enumerates his various publications (Henning Witte, Diarium:

biographicum, Danzig, 1688, fol. Ppp 2r). In his letter of October

4, 1606, Hafenreffer

quarrel with the other Tübingen nicanism

with

Scripture

(see above,

professors

informed

Kepler

about

over the reconcilability

fn. 131). It was

Samuel

Mastlin’s

of Coper-

Hafenreffer’s father,

the professor of theology at Tübingen University, who had advised Kepler to suppress the chapter in his Cosmographic Mystery which sought to harmonize Copernicanism with the Bible (see above, fn. 32). Nevertheless, Kepler wrote to Mastlin that Matthias Hafenreffer “urges me to press on vigorously with these [Copernican] hypotheses so far as they benefit astronomy. I now really believe much more what I had previously thought:

the man is not opposed to Copernicus,

but among the other theologians he must stand up for (what they think is) the Bible's authority. Therefore he does not tell me his true opinion" (Gesam. Werke, XIII, 231:497-502).

386. See fn. 113, above.

Kepler’s Notes on the Dream

143

50 far as the fact is concerned which is adduced as the explanation of the diminished diameter, I do not deny the fact in itself. Hence

I must

also explain why

it cannot

be

the

cause

of this

cast

a shadow.

diminution. The reason unquestionably is that when transparent

objects ?*" are

placed

in

sunlight,

they,

too,

I

proved this in my Optics by experiments with a glass sphere full of water.?* The sphere both permits the sun's rays to pass through it, and also concentrates them to such an extent that they set clothing on fire and ignite powder. But it deflects the transmitted rays into a different place, whereas the edges of the sphere meanwhile cast their shadow in straight lines from the sun. If, on the other

hand, no shadow is formed wherever sunlight can pass through,

what about those lunar eclipses, which we often see, when both luminaries are above the horizon? ?9 The sunlight has passed through our air here, and continues right on to the moon. The earth

presents no obstacle, because both luminaries are above it. Conse-

quently, what is it that envelops the moon in shadow at this time if 387. In his Optics Kepler said: “The essence of a transparent

insofar as it is transparent,

is not light, whether

present

[pellucid] body,

or absent, but only the

internal structure of the body. This essence is not taken away from a transparent

body by shadows; hence it is not put there by light” (Gesazz. 388. Kepler employed the glass sphere full of clear water as vice in his Optics, Ch. 5, Sec. 3 (Gesam. Werke, II, 162). Later with regard to the shadow cast by the earth's atmosphere, he

Werke, II, 46:4-7). an experimental deon, in Ch. 7, Sec. 2, said: "Since air, too,

contains something opaque, this shadow is opaque in quality, especially around the edge, just as every globe full of water, when exposed to the sun, casts a shadow" (Gesam.

Werke,

II, 236:23-25). How

Kepler went far beyond

his predecessors in

using the sphere of water was analyzed by Vasco Ronchi, Optics, tbe Science of Vision, translated from Italian by Edward Rosen (New York University Press, 1957), p. 42. 389. Mastlin presided over a Disputatio de eclipsibus solis et lunae or Disputation concerning Eclipses of tbe Sun and Moon (Tübingen, 1596), in which the defense was undertaken by Marcus von Hohenfelder (one of the three brothers

mentioned in Appendix C). In Thesis 55 of this disputation (p. 19), Mastlin said:

“On July 7, 1590 [Gregorian July 17, 1590; Oppolzer, Canon of Eclipses, p. 368, No. 4319], when the center of the sun was emerging above the horizon, we here at

Tiibingen saw the moon already eclipsed on its eastern side to the extent of sev-

eral digits while its altitude was almost 2°; on the other hand, when the center of the moon was disappearing in the west, we noted that the sun had an altitude of 2° above the point where it had risen. The moon set, however, before it attained

maximum obscuration.” This passage was quoted by Kepler in his Optics to support his assertion that “the moon is eclipsed while the sun and moon are visible

above the horizon" (Gesam. Werke, II, 126:33-37, 236:30-31). As a unit for estimating the extent of a partial lunar eclipse or of a lunar phase, a digit was onetwelfth of the apparent diameter of the full moon (see below, fn. 392).

144

Kepler's Notes on the Dream

not our air, obstructing the direct rays of the sun? Hence, by means of the rays passing through the air and refracted in it, the deflected radiation of the sun does not do away with the shadow of the earth’s air, and therefore it will not do away with the shadow of the moon’s air either. So much, then, for this first proof of air on the moon. The second argument for air around the moon is contained in

Thesis 148. When the occultation of a star by the half moon begins

with the moon’s dark side, that side seems nearer to the center of the moon than does the opposite bright edge. When the full moon is about to occult stars, it seems to take them first within the embrace of this bright tunic, through which they shine; then, finally, it hides them behind its body and occults them completely. You

have an observation of this kind in the Rudolphine

Tables, pre-

cept ?? 133, page 94, concerning a conjunction of the moon

and

Venus.??! The fourth argument, in Thesis 150, is also of the same

kind: when the young moon is seen with a feeble and pale light over its entire body alongside its bright crescent or sickle, at that time the circumference of the bright crescent appears much wider, I say, than the opposite circumference of the body. The disputant believes that the crescent’s bright light comes from the expanse of the lunar air jutting out beyond the body. Add also the fifth argu-

ment, in Thesis 151: the moon’s crescent is never estimated to be

narrower in width than one digit," although sometimes the moon is seen both full and new on the same day, with the illuminated portion taking up barely 1/80 of the diameter. At this time, the disputant contends once more, that tunic of air is seen projecting beyond the edges of the body. I did not regard these three arguments as satisfactory evidence 390. As a manual of instruction for those who wished to use his Rudolphine Tables, Kepler provided 209 “precepts.” Since he here cited precept 133 as being on page 94, the Rudolpbine Tables had already been printed, and therefore this last Note 223 on the Dream was written in 1627 or thereafter. 391. "On January 3o/February 9, 1625, in the evening, at Erbach, Ulm, Tübingen, and everywhere in Swabia, Venus seemed to be almost in the embrace of the

crescent moon

or, according to others, almost to cling to the left horn of the

moon, and from that moment gradually to move around the lower bright hump of the moon. Hence, it may be understood that between the setting of the sun and of Venus there was, so far as sight is concerned, a central conjunction of the moon

and Venus (Frisch,

according

to longitude, even though

the moon

was farther north"

VI, 701:1-6).

392. "Ihe entire body of the moon is divided into twelve parts or digits" (Kepler, Optics; Gesam. Werke, II, 207:36-37).

Keplers Notes on the Dream

145

for so considerable an extension beyond the body of the moon. I connected the cause of the phenomenon with the process of vision. For at night the pupil ?? of the eye dilates in a natural movement. More abundant light enters from a point of the visible source and broadly affects the visual spirits in the retina. The same spreading on the retina happens by day also, when the eye is turned toward a strong light. In this way the image of visible objects on the retina is

spoiled, since the bright parts expand and encroach on the border-

ing dark region. But this picture on the concave retina within the eye corresponds exactly and invertedly ??* to the vision of the ex-

ternal visible object. In a note to his Thesis 151 the author ack-

nowledges this solution, too, without mentioning my name, and he somehow rejects it on the ground that the same things happen also by day. But the phenomenon by which I refute his explanation, although more conspicuous at night, nevertheless occurs also in the daytime. Yet some evidence in favor of air on the moon is provided by this material, especially the fourth and fifth arguments. For the sun's rays pass through the lunar air and make it very bright. Hence the limb, even though otherwise capable of casting a shadow, absorbs this brilliance of the air and strongly affects the vision. This strength corresponds to the effect and stimulation diffused in the retina, and therefore, also, to the appearance of so wide a bright part in the visible object. The premature reemergence of the moon is caused by that appearance, not, of course, by its real width, but by its real strength and brilliance. I do not say that the real visible width of the crescent causes the apparent width, as though the two were commensurate. But the real brilliance causes the false and excessive width on account of the powerful stimulation of the retina. See how the similar arguments of David Fabricius were rebutted by me in this way in the introduc-

tion to my Ephemerides.°”

393. The importance of Kepler’s discovery that the pupil functions as a delimiting diaphragm in the process of vision is emphasized by Ronchi, Optics, the Sci-

ence of Vision, p. 43.

394. Kepler’s right to be regarded as the first man who explained how human beings see is derived in part from his correct understanding of this inversion. The difficulties which it created for his greatest predecessor are set forth by Ronchi,

ibid., pp. 29-30.

395. “The picture of objects on the retina corresponds to the vision of those objects. But in the retinal picture the bright spots are in actual truth enlarged, and

they

take

up

a bigger

space

than

is proper.

This

enlargement

may

be

caused

bv

a

146

Keplers Notes on the Dream

I have passed over the third proof, adduced by the disputant in

his Thesis 149. The edge of the shining moon 1s bright and pure

and without spots, whereas in the middle the moon appears all full of spots. The reason undoubtedly is that the lunar air is thin in the middle of the body and shallow on the sides, but toward the edges it looks deep to the eye. For in like manner, on the plains of the earth, the air overhead, even though lit up by the sun, does not

affect the vision strongly, and does not hide the bigger stars from

those who

look up from

a deep

well.”

But the air which

sur-

rounds distant mountains turns white because it offers a passage of great depth to vision. It tinges the more remote mountains with an azure color. Indeed, it makes them absolutely dark. In the absence of the sun, it even obscures the brightest stars as they rise. Thus there generally are no clouds overhead, or they are scattered and transparent; but they are always very thick toward the horizon, even when they are at the very minimum overhead. These are Mastlin’s proofs of air on the moon; this is their force.

Afterwards he propounds Thesis 152, the next to the last in the lit-

tle book, in which he compares the air on the moon to the air surrounding our earth. To our dawn he likens that brilliance of the limb which is the cause of wonderful spectacles. And he raises our eyes upward, as I do toward the moon, whence they will recognize the very similar phenomena on our earth. At the end he appends a note saying: "Whether that air, like ours, condenses into clouds which, on account of their opacity, take on the appearance of very solid bodies and for that reason look incandescent or fiery, as among us, when the sun rises or sets, I leave undecided. Experience has certainly taught us that that

enveloping ??? brightness limpid." And

appears

at various

times

he adds evidence right in line with my

more

or less

hypothesis:

"In the year 1605 on the eve of Palm Sunday in the body of the defect in the eye and by a confusion of adjoining pictures at the boundary common to exceptionally bright areas; or it may be caused also by the nature of light and the [visual] spirits which, being akin to light, are stimulated by the contact, as it were, with parts of the bright pictures, rides, p. 21; Frisch, II, 113:23-28).

and

expand

on

the retina"

(Epheme-

306. What Kenler had in mind here was the famous passage in Aristotle's Gen-

eration of Animals, Bk. 5, Ch. 1: “Stars are sometimes seen by men in pits or wells"

(780^ 21-22).

397. The misprint circumfluuss in the Somnium to circumfluus by Frisch (VIII, 66:10 up).

(1634 ed., p. 79)

was corrected

Kepler's Notes on the Dream

147

eclipsed moon,?? which displayed the color of red-hot iron, a blackish spot darker than the rest of the body was seen toward the north. You would have said that extending over a wide area there were clouds laden with rain and stormy showers of the kind which, it frequently happens, is seen by those who look down from the summits of high mountains toward the lower places in the valleys.” Some time later I entered into conversation with him, when he told me that that spot was of no ordinary size, but took up half the diameter, more or less??? The recollection of this remark finished this last part of my Dream. In repeating it I put an end to these Notes. 398. In a letter to David Fabricius, Kepler described the moon in the eclipse of

April 3, 1605 (Oppolzer, Canon of Eclipses, p. 368, No. 4342) as "having a color like that of dilute blood, as if someone had wrung out a cloth soaked in gore"

(Gesam. Werke, XV, 277:1484-85). All the observations of this lunar eclipse which Kepler could collect were carefully examined by him as part of his analysis

and comparison of 46 lunar eclipses from 1572 to 1625 (Frisch, III, 601-3). 399. This conversation may have taken place in November or early December, 1617, when, as Kepler wrote to Wackher von Wackenfels: "I visited Mastlin frequently and talked with him about all the parts of the [Rudolphine] Tables” (Gesam. Werke, XVII, 254:35-36). In a letter of April 11, 1619, to the theologian Matthias Hafenreffer, Kepler recalled “that memorandum which I sent you last

year from Mästlin’s house”

(ibid., 348:230-31).

GEOGRAPHICAL IF YOU

PREFER,

SELENOGRAPHICAL

APPENDIX

To

the Very

OR, '

Reverend Father Paul Guldin,

priest of the Society

of Jesus, etc.

O venerable and most learned man, and honorable patron. There is hardly anybody with whom at this time I should prefer to talk about astronomical studies face to face than with you, if besides the pleasure of this conversation some other profit from my journey * would be likely in this turbulent period when the entire court ? is worried about war problems.’ For this reason I found all the more delight in the greeting from Your Reverence, which was reported to me by the members of your order who are here. In I. As the Appendix to his Dream Kepler used a letter which he had written to Paul Guldin (see Appendix L). In all likelihood it was printed under Bartsch’s supervision (see Introduction, p. xxi). It is listed in Gesam. Werke, XVIII, 151, but

is not reproduced there, presumably because it will be printed with the Dream in Gesam. Werke, XII, when that volume is ready 2. The contemplated journey would have taken Kepler due east down the

Danube about a hundred miles from Linz to Vienna, where Guldin was teaching mathematics when Kepler wrote this letter. 3. The court of Emperor Ferdinand II in 1623 resided at Vienna. This fact confirms what is said in fn. 2, above, and in Appendix L about the destination of our letter.

4. The opening phases of the Thirty Years’ War

(1618-48)

had ended with the

suppression of the Protestant revolt in Bohemia (1620) and the victory of Emperor Ferdinand II’s Counter-Reformation in the Palatinate (1622). But these very Catholic successes led to fears in Vienna that a new and more powerful coalition against the Habsburg empire was beginning to take form in 1623.

149

150 particular, traordinary in this field from whom

Geographical Appendix to the Dream Father Zucchi? could have entrusted his most exgift, I mean his telescope,? to no one else whose work pleases me more than yours. Since you are the first I hear that this treasure is to pass into my possession,‘

you are also the first to whom I think I should offer some fruit of

literary enjoyment, derived from experience with this gift.

5. Niccoló Zucchi (1586-1670) first came into contact with Kepler by bringing

him a copy of Scipione Chiaramonti’s Anti Tycho (Venice, 1621), a misguided effort to refute Tycho Brahe's thesis that comets follow an orbit beyond the moon. Kepler wrote his Shieldbearer for Tycho in reply to Chiaramonti’s Anti

Tycho, In responding to Kepler's Shieldbearer, Chiaramonti said: “I presented a copy [of Anti Tycho] to the most illustrious Cardinal Alessandro Orsini. He took it... with him into Germany, to be given to Kepler by the Cardinal's confessor, Father Niccolo Zucchi, who accompanied him on that trip to Germany" (Chiaramonti, Apologia, Venice, 1626, p. 63).

On March 28, 1624, Kepler wrote to Guldin: "Receive from the hands of my courier a copy of my Harmonics and [of the second edition of my Cosmographic ]

Mystery .... In exchange I request the following service of you. As soon as you send a letter to Father Zucchi, tell him that you, who were the intermediary for

the gift which he gave me, are now being asked by me to be also the go-between

for my return gift" (Gesam. Werke, XVIII, 172:7-12). In a letter of August, 1625, to Guldin, Kepler said: “I greet Father Zucchi too” (ibid., 245:127) In his Optical Philosophy (Lyons, 1652-56), I, 126, Zucchi dates his unsuccessful

attempt to construct the first reflecting telescope as 1616; see Hans Weyermann, "N. Zucchi und sein Spiegelfernrohr," Die Sterne

(1963), 39:229-30. In 1638 Galileo

was told that Zucchi "puts Venus closer to the sun than Mercury, because Venus

stands for beauty and Mercury

for brains"

(Galileo, Opere, XVII,

316:27-28). An

account of Zucchi will be found in Ireneo Affó and Angelo Pezzana, Mernorie

degli scrittori e letterati parmigiani (Parma, 1789-1833), V, 170-76; VI, Pt. 2, 773-79, 981; VII, 668-69. 6. For Kepler's use of perspicillum as a technical term to denote optical equipment, see Edward Rosen, The Naming of tbe Telescope (New York: AbelardSchuman, 1947), pp. 3-4. 7. Ihe announcement that Zucchi’s telescope was to be a gift to Kepler, not a loan, must have been contained in a letter from Guldin, which was communicated to Kepler in Linz by Guldin’s fellow-Jesuits there.

Ten years before, Kepler advised the cartographer Ottavio Pisani: “If you write

any letters [to me], give them to the postal service to be transmitted to the Imperial Court. But if the emperor is at Vienna or Prague, and I remain, as I hope, at Linz, letters entrusted to the rectors of Jesuit universities will be taken care of

properly. For here at Linz there are members of that Society, to whom letters are

sent by their fellow-Jesuits, and the Jesuits at Linz will forward them to me without any reluctance” (Gesam. Werke, XVII, 97:35-39). It may well be, then, that Zucchi brought the telescope with him from Italy to Vienna, where he handed it to Guldin, who in turn sent it on to the Jesuits at Linz, to be delivered to Kepler. 8. Since Kepler had already obtained results from experience with Zucchi’s tele-

scope before hearing that it was to pass into his possession, presumably he originally had the impression that it was a loan rather than a gift (see above, fn. 7).

Geographical Appendix to the Dream Indeed, why should I not speak? If you direct your mind the towns on the moon, I shall prove to you that I see them Those lunar hollows, first noticed by Galileo,'? chiefly mark moonspots (2), that 1s, as I show;!! depressed places in the flat

151 to? (1). the area

of the surface, as the seas are among us (3). But from the shape of the hollows I conclude (4) that those places are, I would say,

swampy

(5). And in them the moon-dwellers usually measure out

the areas (6) of their towns for the purpose of protecting themselves (7) from the mossy wetness (8) as well as from the heat of the sun (9), and perhaps even from enemies (10). The design of the fortification is as follows. They drive a stake down in the center of the space to be fortified (11). To this stake they tie ropes (12) which are either long or short (13) depending on the size of the future town. The longest I have detected is five German miles (14). With this rope fastened in this way, they move out to the future rampart's circumference (15), as defined by the ends of the ropes (16). Then the entire population assembles to do the digging for the rampart (17). The width of the ditch is not less than one German mile (18). They take all the excavated material (19) in-

side some towns (20). In others, they have built partly outside and

partly inside (21); thus the rampart is constructed in two sections (22), with a very deep ditch in between (23). The individual ramparts return upon themselves, as though a pair of compasses had

made them perfectly round (24). They achieve this circularity by equalizing the ropes stretched from the stake in the center (25). Thus the deep, but though it periphery

result is that not also the center of were the navel of is raised up high

only is the ditch pushed down quite the town looks sunken like a chasm, as a puffed up belly (26), while the entire by the pile of material removed from

the ditch (27). For from the ditch all the way to the center would

be too long a distance from which to clear away the material (28).

Hence the moisture of the damp ground collects in this ditch (29). Whatever space is enclosed by the ditch is drained by it (30). When it overflows with water, it becomes navigable (31). When it has dried out, it can be crossed as a land route (32). Therefore, wherever the sun’s strength assails them, those who are 1n ? the 9. Ad was inserted by 10. See Kepler's Notes 11. See Kepler’s Note 12. The misprint Quin

Frisch (VIII, 67:15) to improve Kepler's Latin style. on the Dream, Note 154. 1 (xir) on the Geographical Appendix. in the Somnium (1634 ed., p. 82) was corrected to qui in

152

Geographical Appendix to tbe Dream

center of the space (34) betake themselves toward that part of the circular ditch in the shadow of the outside rampart (33); and those who are beyond the center take refuge in the part of the ditch turned

away

from

the sun, in the shadow

of the inside rampart

(35). And thus for the fifteen days during which the place is unin-

terruptedly

scorched

by

the

sun,

they

follow

the

shadows

as

peripatetics in the true sense of the word, enduring the heat (36). Let these comments be placed before you as a question to be settled piece by piece on the basis of phenomena (37) discovered by the telescope, if those phenomena are brought into agreement with these conclusions by means

metaphysics (38).

of the axioms of optics, physics, and

But these are playful remarks, etc.

by Frisch (VIII, 68:11). In the present translation, Kepler's Note 34 on the Geographical Appendix precedes Note 33 because strict adherence to Kepler's Latin word order would have produced an awkward result in English.

NOTES

ON

THIS

APPENDIX

1. A

certain

statement

is also the substance

of the

following

theses. At [Note] number 37 I promised that I would try to prove

them on the basis of the phenomena, and at [Note] number 38, on the basis of the phenomena brought into agreement by means of the axioms of optics, physics, and metaphysics. Hence I shall execute that plan in the following notes. I. Phenomenon: on the surface of the moon, when it is thought to be exactly at half-moon, beyond the straight line of separation, where it passes through the spotted areas, the bright part extends or continues, and penetrates into the other or dark part of the moon. n. Io this phenomenon apply the following unchallenged axioms. The sun’s rays are rectilinear. The moon is a spherical

body. That separation on the moon is nothing but the terminator

of the illumination coming from the sun; on this terminator the outermost rays of the sun strike the moon in such a way that the nearer and illuminated part of the moon is turned toward the sun, whereas the more distant part, which is dark and not illuminated on account of its convexity, is turned away from the sun. Therefore, if the sphere were uniform and perfect, the separation should be a

perfectly straight line at quadrature, or a perfect ellipse before and

after quadrature. It rigorously follows that where the separation 1s a line which is not perfectly straight but is jagged, as it were, with bright teeth intruding into the dark part, there the lunar globe 1s not perfectly spherical. Those bright teeth are portions rising above the surface of the spotted areas, or the spotted areas are low as compared with the nearby bright areas. As a result, the same

rays of the sun which cannot reach the spotted areas beyond the

separation

(since the rays are obstructed by the convexity of the 153

154

Kepler's Notes on the Geographical Appendix

spotted areas) still reach those portions or bright teeth, as though they were at a greater elevation from the center of the lunar sphere. Their convexity does not turn them away from the sun

(for in that case the separation would pass through them, too, in a

straight line), but the height of those projections increases as you advance farther into the dark half of the moon. 11. Phenomenon: where the line of separation passes through

the bright parts, it becomes uneven, so that it looks like a saw or a break across a piece of wood. IV. Therefore,

in the part where

the moon

is purely

bright

some portions near the separation rise up high. Near that same separation the portions next to these high portions slope down, with the heights and slopes alternating. But this is the definition of unevenness. Hence, on the moon’s surface,’ the parts which shine with pure light are in fact uneven.

v. Phenomenon: on the other hand, where the line of separa-

tion passes through the spotted parts of the moon's surface, it is perfectly straight. VI. Therefore, the spots on the moon are portions of a smooth and perfectly spherical surface. vit. Phenomenon: when the separation passes through the

spots, certain dark gaps are seen extending from the obscured part

of the moon into the illuminated part of the moon. These gaps cut the spots off, as it were, from the purely bright parts. virt. Therefore, the sun’s rays illumine both the bright parts and the spotted parts on both sides of those dark gaps in the illuminated half. But the region which the gap crosses is not illuminated. IX. However, according to ri, the bright parts are high, and the spotted parts are low. Therefore, those gaps are nothing but the shadow of bright parts, as if these were mountains or coasts, the shadow being cast onto the spot as if this were a plain or a sea. X. Phenomenon: in the obscured part of the waxing moon, near the separation, shining points are seen. After the passage of several hours they become brighter, until they merge with the illuminated part near the line of separation. Then it is apparent that those points belong to the bright part of the moon, and not to the spots. 1. The misprint superficiem in the Somnium superficie by Frisch (VIII, 68:2 up).

(1634 ed., p. 84)

was corrected to

Kepler’s Notes on the Geographical Appendix

155

xl. Therefore, from that part of the surface which is not yet

struck by the sun’s rays some peaks must rise up so high that they can be reached by the sun’s rays and, again, the entire area around

such peaks is higher than the spotted part of the surface. xi. Phenomenon: the features described in 1 and vu are observed to be alike both in the first quadrature and in the last quadrature around exactly the same spot. Both of the separations pass through it, each at its own time, but in opposite parts of the spot. xi. Therefore the spot, which according to rm is low, and according to vi is smooth, is surrounded on all sides by bright areas which (according to 11) are high and (according to 1v) are uneven. xIv. Phenomenon: in the illuminated half near the separation, numerous dark little lunes or sickles are seen, with their horns turned toward the line of separation. Facing these dark sickles, with their horns touching, are, as it were, opposing sickles, which have a

stronger light than the rest of the surrounding area.

xv. Therefore, in the illuminated half there are low circular places or hollows, which cannot be reached by the sun's rays on the side toward the sun. In these places the remaining part of the

hollow, which is high on the side toward the separation, 1s more di-

rectly exposed to the sun's rays, and is more strongly illuminated than the rest of the plain outside. xvi. Phenomenon: one such bright sickle is of remarkable size. Its horns touch the line of separation. Opposite to it in the illumi-

nated part 1s a dark surface which is gibbous, as though it had been

cut away from the sickle in a full circle. These contrasts of light and darkness within a circle are interchanged in the opposite quadratures. xvul. Therefore, also in the obscured half, there is a huge hollow or pit. Its rim extends its curvature toward the sun, and casts a shadow on the bottom of the opening. But the half of the rim which proceeds away from the sun toward the obscured half of the moon receives the rays of the sun which are admitted through a gap or hole in the opposite rim. xvi. Among us earth-dwellers the causes which shape the surface of the earth are of two kinds. For either this shaping 1s conscious, like the cultivation of the land, construction of intrenchments, and diversion of rivers; or it is produced by the movement of the elements, in which case the elementary qualities giving rise

156

Kepler’s

Notes

on

the Geographical

Appendix

to motion and change of shape are wetness and dryness, hardness and friability. For instance, liquids flow down to places closer to the center of the earth, until they come to a common equilibrium. Among dry things located near flowing water, those which are harder are more durable; but those which are softer or friable gradually disintegrate. I shall use a clear example. You ask who built those hills scattered through the fields of Bohemia, where the re-

gion is reduced to a narrow strip facing the mountains

which

border on Meissen. If you look at the row of those hills from a high mountain in the distance, you will say that they are the work

and, so to speak, the tombstones of the Giants. I shall name their creator. It is the river Elbe which, as it found its course down

through the mountains, steadily lowered and dug out its bed. Frequent rains poured down on the open plain’s fertile land, which was gradually washed out over a long period of time, during which the eroded soil was carried down into the Elbe. Finally, there are rocks that once were underground but stand out now that the earth has been taken away. Because of their hardness they have lasted, while the earth around them crumbles away on account of its friability. This is the reason why on most mountain tops a heap of rocks is found, which thoughtless people will say was once a fortress. This is the cause that has scattered many rocks throughout the sandy fields of Silesia. For since the earth is level,” the current

in the rivers is not strong. Hence only the little glens are generally

washed out, like ditches, by the perpetual flowing of the streams. The higher plains are not affected, except to the extent that the rains erode the sides of the field. When the glens are washed completely away, and the higher plains are worn down in a long course of time, the rocks which once lay covered with earth are laid bare.” 2. Ihe word is plena (“full”) in the Sommnium (1634 cd., p. 86). Kepler had in mind, however, a word intended to explain why the rivers in Silesia are sluggish. Hence what Kepler was thinking of was undoubtedly plana (“level”).

3. Kepler's description of these features of the Silesian landscape seems based on personal observation. If so, he has given us a clue to the date when he composed his Note 1 (xvım) on the Geographical Appendix. He moved to Zagan in Silesia

on July 26, 1628

(see Appendix

A, p. 182), and it may

well be that he composed

the Notes on the Geographical Appendix after that date.

The 1020. Latin Since

creation of mountains by erosion was first described by Avicenna about A.n. Around A.D. 1200 Avicenna’s description was translated from Arabic into in a condensed form, which was then appended to Aristotle’s Meteorology. this work was closely studied by Kepler, he may have encountered the fol-

Kepler’s Notes on the Geographical Appendix

157

xix. The mind is the source of orderliness. Nothing arranged by

the mind is out of order and confused unless the mind, using its own judgment, has given free rein to instrumental causes different from itself. It therefore follows that those things which are out of order, insofar as they are out of order, are the result of the movement of the elements and the composition of matter. xx. On the surface of the moon’s body, so far as the more visilowing passage: "Certain soils are soft, whereas others are hard. The soft soils are carried away by flowing water and by winds. The hard soils remain, and that is

how a height is created"

(Avicenna, De congelatione, eds. E.J. Holmyard

and

D. C. Mandeville, Paris, 1927, p. 48:12-14). Or perhaps Kepler was influenced by the following remarkable discussion in George Agricola's Origin and Causes of

Things under the Earth, of which

three Latin editions had appeared

by

1612:

“Most mountains are created by water, as is plainly evident. For the mountain streams wash the soft earth away first, then they remove the harder earth, and afterwards they dislodge the rocks, too. Thus in a few years they dig out a level field or a sloping place to some depth. This process can be observed in a moun-

tainous region even by inexperienced persons. Moreover, by chipping at the same hollows to an astonishing extent through many generations of human beings, the streams make a steep height on both sides. Out of this height, as it rises, earth slips down when it is loosened by steady rains and pushed out by freezing weather. Unless the rocks are very solid, they fall into the hollow below, because their cleavages are similarly weakened by moisture. This action continues until the

steep height is changed into a slope. Yet each is called a mountain, just as the lowest part of that open height is termed a valley. The same result is brought about by brooks and even more by rivers, as they descend

and flow. That 1s why

they are often seen to run either between very lofty mountains created by themselves or near their foothills. These

are low,

and

on

both

sides broad

fields are

frequently visible. Where their width ends, ridges rise or hills or lofty peaks, which now look like a very long mountain or cliff, whereas they were low-lying

banks several centuries ago. This

is indicated by the old and higher plains of the

same banks, which sometimes spread out very far. But such high places are quite distant from

one another. For when

the rivers overflow

their banks, they

gener-

ally destroy the one consisting of more fragile material, but sometimes thev demolish both banks. Thev take hold of the material and add it to their bed. They continue to do this until they meet very firm rocks which check their onslaught

and divert them elsewhere. Hence we see them twisting and turning this wav and that. Sometimes new river beds are formed and the old ones abandoned. Sometimes the lower plains of the fields, lying beneath those heights, become quite broad. The depths which now contain the seas were once not all there. Nor were the mountains, which control and break their flow. On the contrary, in many places there was level field, before the wild sea with its raging tide was driven onto it by the power of the winds. In like manner the force of the water completely destroys and smashes hills and mountains. Yet these numerous and exten-

sive transformations of regions do not seem to most people to be occurring precisely when they are occurring, because the memory of mankind has forgotten

on account of their remoteness when, where, and how these transformations began" (De ortu et causis subterraneorum, Dk. 3; ed. Basel, 1546, p. 37).

158

Kepler’s Notes on the Geographical Appendix

ble parts are concerned, some disorder is observed, some parts being high and others low, some smooth and others uneven. Therefore, in the body of the moon there must be something like our elements and their aforementioned qualities. Let us be permitted to call these qualities by the same names, for instance, hard, friable, dry, and wet. xxt. Therefore the moonspots are a liquid which, by its color

and softness, dulls sunlight; by flowing smoothly around the center of the sphere, it causes both the lowness and the smoothness of the

surface. It is the mountains which receive the brightness from the

sun; because they are dry and hard, they also reflect the sunlight

brilliantly. They rise high above the surface of the water, and because their parts are not equally high, they make the moon's surface uneven. xxii. Phenomenon: among the spots there is a difference with respect to their darkness, some being blacker than others. For instance, at some distance from the center of the disk toward the south there is a spot which looks like an Austrian shield (since it 1s a deep black at the top and on the bottom).* In the middle, however, it 1s divided by a band of uniform width, which 1s a little less dark than the rest of the space, but less bright than the bright parts of the moon. xxii. Therefore the spotted parts on the moon, that is, the wet regions, differ in their degree of wetness, some being drier, others wetter. Hence there is something like our swamps and something like our pure seas. For in like manner in our swamps, too, grasses, reeds, rushes, and canes grow, while everywhere there are also hard, dry, and white soils, which reflect the sun's rays more brightly.

xxiv. Phenomenon: through the best telescope the spots located

near the line of separation look to the eye not unlike a boy's face,

disfigured by pimples bulging far out, if this swollen face is illumi-

nated by light whose rays come from either side. For example, if

the rays come from the left, the face looks like the first quadrature; but if from the right, like the second quadrature. For just as on such a face all the little bumps on the pimples are illuminated from the side which is toward

the light, so also scattered about in the

4. Such a shield will be found depicted Abt. 4, Teil r, plates 249, 251; Abt. 5, Teil

in Siebmacher’s r, plate rr.

Wappenbuch,

Band

4,

Kepler s Notes on the Geographical Appendix

159

spotted parts of the moon little round areas are observed, all of which are bright on one side and dark on the opposite side. xxv. But if sunlight fell also on these little areas from the side on which they are bright, the conclusion would have to be that there are actually as many little bumps on the moon as there are little areas of this kind; these bumps, rising to a height, would receive

sunlight and cast a shadow in the direction turned away from the

sun. But we see the opposite: those parts of the little areas which are toward the sun are dark, whereas those parts which lie on the

side opposite the sun are bright. Consequently a shape which is the opposite of the shape described above must be attributed to those little spaces: they do not rise up in little hills, but are sunken down in round hollows. For thus it happens that the rim facing the sun casts its shadow into the bottom of the hollow, whereas the oppo-

site rim is more brilliant because it receives the sun’s rays at a more direct angle. xxvi. Axiom: when things are in order, if the cause of the orderliness cannot be deduced from the motion of the elements or from the composition of matter, it 1s quite probably a cause possessing a mind. The axiom should be clarified by examples. A straight line 1s an orderly thing. A lead ball, fired from a gun, travels in a straight line.? This motion comes, not from a mind, but from the composition of matter. For the nitrous matter of gunpowder explodes when touched by fire, and expels the ball where this obstructs the expansion. Therefore, since the obstruction occurs along the entire

length of the iron barrel, throughout it a powerful imprint of ex-

pulsion in a straight line takes place. In like manner the motions of heavy bodies are rectilinear, so that this kind of order, I mean a straight line, is somehow a property of heavy bodies and especially of light, whose rays are, so to speak, an immaterial body moving in an instant? In like manner the housing of a snail has the orderly

s. Kepler was initial movement gravity modified years before the

thinking only about the first part of the was widely believed to follow a straight the trajectory. This idea was repeated trajectory was first proved in 1632 to be a

projectile's path. This line until the force of by Kepler only a few parabola in the absence

of air resistance; see A. Rupert Hall, Ballistics in tbe Seventeenth bridge, England: University Press, 1952), pp. 38, 83, 86.

Century

(Cam-

6. Kepler stated his conception of the nature of light and its velocity more fully

in his Optics:

Thus

"Since

the medium

light possesses no matter, it therefore

offers no resistance

to light, because

has no weight

either.

light lacks the matter

160

Kepler’s Notes on the Geographical Appendix

shape of a spiral. Yet this proceeds, not from the mind of an architect, but from the composition of matter. For toward winter the snail twists itself into the shape of a cone. When it is twisted into this shape, a sticky liquid flows over it and hardens into a shell, the circles being added according to the number of contractions. In like manner the honeycombs of bees become hexagonal on account of the material composition of the bodies, when they are squeezed together as tightly as possible. On the other hand, arrangement by fives in flowers is something orderly, and since it cannot be derived from matter, it is therefore ascribed to the creative faculty, which somehow participates in number and thus in reason. In my book on

The New Star, Chapters 26 and 27, I have discussed the question

whether the close agreement of many things in one coordinated series can be attributed to blind chance.‘ xxvil. Phenomenon: those hollows which are sunken down into the moonspots are perfectly round, so far as we can reach them with our eyes. But they are not all of equal circumference. There is even a place where they seem to be arranged in a certain order, like a quincunx. xxvii. If we apply the foregoing axiom to these phenomena, we shall arrive at the following conclusions. In general on the surface of the lunar sphere, so far as the mixture of high and low parts is concerned, chance and the composition of matter are predominant. Soil is eroded away from the underground rocky ribs. Valleys are washed out, so that mountains rise up. Water flows down into the low-lying areas, marked by the spots. There it is distributed in a state of equilibrium by the rectilinear tendency of all its parts toward the same center of the lunar globe. But in the spotted parts of the moon the perfectly round shape of the hollows and their arrangement, or a certain equality of the distances between them, are

artificial and produced by some architectural mind. For that scoop-

ing out into the form of a circle cannot be accomplished by any motion of the clements, unless you say that the moon's surface is which causes resistance. Werke, IT, 21:13-15).

Consequently

the

speed

of

light

is

infinite".

(Gesam.

7. Why did the nova of 1604 appear near a great conjunction of the three outer

planets

in a fiery sign of the zodiac

at that particular

time?

This

question

was

answered by Kepler in his characteristic way: not blind chance produced this re-

sult, but divine 291: 15-18).

providence

with

a view

to human

salvation

(Gesam.

Werke,

I,

Kepler’s Notes on tbe Geographical Appendix

161

covered by very deep sand, at the bottom of which a hole has been made, and that beneath the crust there is an empty place into which the sand flows. This cannot be asserted on account of xxi. For liquid prevails in those areas and, if it were given an exit, it would flow away and drain those areas, so that they would become white and shining instead of spotted. Much less can the spacing of most of the spots with relation to one another be produced by the motion of the elements. XxIX. From the foregoing we must conclude, it seems, that on the moon there are living creatures, capable of reasoning with a view to constructing those orderly things. But they are endowed with a size of body not to be compared with those mountains, in which no orderly arrangement is manifest. For in like manner on the surface of the earth, too, men do not make mountains and seas (a Xerxes is rare,? a Nero is rare,’ nor are their works to be compared with the natural formations of mountains and seas). But on the earth men do build cities and castles, in which orderliness and art are discernible. Indeed, the surface of the spheres seems to have been left to blind chance for this very purpose, that in arranging it and embellishing parts of it there may be room for the exercise of reason. xxx. Phenomenon: if you look at such hollows very carefully, and imagine a straight line drawn from the sun through the center of the hollow, six distinct areas occur in it, three being light and an equal number dark. It is as though there were a hollow within the hollow. For the dark part of the bigger and outer hollow has its back curved toward the sun. On the other hand, the light part turns 1ts horns toward the sun and toward the dark part, the curvature of the bright part being away from the sun. The same sight appears on the inside of the narrow inner hollow. But on the out8. After Xerxes, king of the Persians, was defeated by the Greeks in the naval battle off the island of Salamis (480 B.c.), “he tried to build a mole to Salamis” (Herodotus,

vill.97).

Herodotus’

account

of

Xerxes’

attempt

to

construct

a mole

to Salamis is rejected as a fiction by Charles Hignett, Xerxes’ Invasion of Greece

(Oxford: Clarendon Press, 1963), pp. 415-17. 9. “The neck from which [the Peloponnesus] projects is called the ‘Isthmus.’ There the above-mentioned [Aegean and Ionian] seas, encroaching in different directions from the north and from the east, eat up its entire width... . Sailing around [the Peloponnesus] is long and hazardous for ships whose size prevents them from being carried across [the Isthmus] on wagons. Hence attempts to dig a navigable canal through this neck were made by [three previous rulers and] Nero" (Pliny the Elder, Natzral History, 1v.4.9-10).

162

Keplers Notes on the Geographical Appendix

side it being horns found rim is which

is bathed in light where it faces the sun, its curved back turned toward the sun; on the opposite side it is dark, the being turned toward the sun. Furthermore, a difference 1s with regard to the outermost rim. For in some hollows this neither more visible nor brighter than the region outside, I said belongs to the moonspots. The dark curve starts at

once with that degree of light with which the spots shine. On the side opposite the sun, behind the intense light of the wall, which is exposed directly to the sun's rays, a lesser brightness follows and

continues through the spotted region. In other hollows, by con-

trast, the outermost rim toward the sun is surrounded by a thin line

of very bright light; but on the side opposite the sun, by a thin line

of shadow, which differentiates the rim from the rest of the region. xxxi. This proves that from the bottom of the hollow there rises a hill which is pressed down again in the middle, like a navel,

into a pit. I pointed this out as early as the year 1625 in my Shield-

bearer for Tycho, page 124.'° It proves also that some of the hollows are scooped out directly from the plain itself, whereas others are, so to speak, fortified against the region outside by a rampart raised up high. xxxi. Ihe multitude of individual works of art shows that they have a multitude of uses, whether they are used by many or by the same user at different times. Yet it stands to reason that the difference in the works corresponds to a difference in the times. Thus the order among those many things demonstrates that one mind

embraces everything. xxx.

From this axiom and from xxix we readily deduce that

on the surface of the moon there is a population capable of reason

to the extent of building those hollows. It has multiplied into very many individuals, so that while one group constructs and occupies one hollow, a different group develops another. For these hollows resemble one another closely, as far as our senses can judge, and they are arranged with regard to one another according to a definite law. This establishes mutual agreement among the creators of the different hollows. 10. "As

a German,

I have

had

occasion

to test lenses brought

Venice. They spread a single moonspot, which takes up barely

to me

from

1/40 of the diame-

ter, so wide that they permit a very clear recognition of a navel rising up from that spot, as though it were a round ditch and of a little dip pushed down the middle of the navel” (Gesamı. Werke, VIII, 366:2-7).

again in

Kepler's Notes on the Geographical Appendix

163

xxxiv. Here add an observation copied out of my Report on my observations of Jupiter’s satellites, which is preceded by the

inappropriate title “Preface to the Reader.” !! I copy the words on

folio 17: ??

I cannot forbear from describing, for the sake of diversion, the ad-

ditional spectacle exhibited to us by the moon, which was waning

(since these days came right after the full moon).1? On the face of the moon above its left eye, opposite our right, there is a rather small

spot, as is widely known, like a very black point. I never believed that

11. When Kepler wrote this derogatory remark about his Report, what he had before him was evidently not the printed work but a handwritten draft. For in the Report as printed, on the first inside page just below the author's name and title,

appears the expression: "Greetings to the Friendly Reader" (Amico lectori salutem; Gesam. Werke, IV, 317:3). These words may well have been substituted by the printer for Kepler's "Preface to the Reader" (Praefatio ad lectorem). In any case they were placed on the first inside page (fol. Azr) and did not constitute the title for which, as Kepler here admits, they were inappropriate. Apparently, then, the printer designed the title page, which presumably was not in front

of Kepler when he wrote the Notes on the Geographical Appendix to the Dream.

Here in his Note 1 (xxxiv) on this Appendix, Kepler refers to his Report as the narratio de visis a me planetis Jovialibus. Somewhat different is the printed title, Narratio de observatis a se quatuor Jovis satellitibus erronibus. 'The difference is historically important because the title marks the first time that the term “satellite,” introduced by Kepler as the designation for the bodies revolving around

Jupiter, appeared in a printed work. Kepler's Report closes with nine short poems by Thomas Seget (see Edward Rosen, “Thomas Seget of Seton,” Scottish Historical Review, 1949, 28:91-95). "With Seget's letter," Kepler informed Galileo, "you will receive a copy of my Report. Yet I cannot hold back a complaint about what

he did in... forcibly annexing his poems to my Report . . . . | often advised him

to publish

his own

compositions

separately. But he had worked

such a position that I could not refuse him without offending

himself into

him. I gave my

permission the more readily because I reflected that in the fullness of time all the

effusions of the frenzied will surely pass away, while Jupiter, together with his

household, will pursue his course forever" (Gesam. Werke, XVI, No. 597:6-19; Galileo, Opere, X, 457:6-17). 12. There is no folio 17 in the printed Report, where the extract copied out by

Kepler for inclusion in his Note 1 (xxxiv) on the Geographical Appendix occurs

at folio* 4v — **ır. Does "f. 17" refer to Kepler’s handwritten draft of the Report? Or does it refer to the Conversation, "f. 17," which is cited twice by Kepler in his Notes 8 and 9 on the Geographical Appendix, just below? The observation in question, as reprinted from the Report, will be found in Gesam. Werke, IV, 320:32-321:32. 13. The words in the parenthesis appear in the 1634 Somnium, p. 9o, but not in the Report. They were not needed in the Report, where “the additional spectacle exhibited to us by the moon” had already been dated “after the quadrature of the

moon” (Gesam. Werke, IV, 320:13). Hence it seems likely that this parenthesis was inserted by Kepler when he was copying the extract out of the Report for inclusion in the Geographical Appendix to the Dream.

164

Keplers Notes on the Geographical Appendix

it was anything but a deep

moon

is waxing,

hollow.

It is less conspicuous

as is natural. For, since it is located where

slopes down, it is presented more

when

the

the moon

directly to the sun than when

the

moon is full. As the sun’s light is averted at that time, it comes into deeper shadow. On the evening of September 4 (in the year 1610),!#

as it was enlarged by the instrument to look like a very broad spot, it had a rusty color and was encircled by a rim of very bright light. But

on the morning of September 5 the rim opened up toward the dark

part of the moon. For the illuminated circle or boundary passed around this spot in a perfectly curved line. But both arms of the very bright rim extended 15 beyond the boundary of the light into the region of shadow. The arms were turned back and bent inwards, like the natural breakwaters by which the harbors of Ancona, Messina, Genoa, and other ports are formed, in short, in a sharp curve. It was the plainest picture of a lake with the shape, you might say, of the Caspian Sea. But in size it was more like the Black Sea or the Jonian Sea. For inside that lake, where it turned toward the body of the moon, there was a brighter little area of land, joined by an isthmus to the very bright shores. Thus there were three different shades: the brightness of the shores and mountains; the rusty darkness of the spot or lake, up to the boundarv of the light; and the intermediate shade (although

it was

closer

to the

darkness

of the lake),

which

was

dis-

plaved by that little area. At nine o'clock in the evening, when the moon had risen, the light had left the entire lake, and the shores were seen in a very beautiful circular curve,

as though

a cut had

been

made

or a trench

had

dug in the moon. Only the peninsula inside the hollow of the was still lit up. The isthmus appeared verv clearly. It looked like the Crimea Black Sea or rather like the Peloponnesus, separated (from the nent) 18 on both sides by dark gulfs. Yet its front was long and the lake directly, unlike the peninsula's, which

been

shores in the contifaced

ran into the lake at an

acute angle. The isthmus was three times as long as it was wide. Remarkably

enough,

in

the

peninsula,

where

it is joined

by

the

isthmus to the mountainous shores, there was a verv bright point, like 14. The words in the parenthesis appear in the 1634 Sommium, p. go, but not in the Report. They were not needed in the Report, which is dated September 11, 1610 (Gresanı. Werke, IV, 322:38-39). But the reader of the Dreamz had to be told

in what year this observation was made “on the evening of September 4.” Hence it seems likely that this parenthesis was inserted by Kepler when he was copying the extract out of the Report

Dream.

15. The

words

utroque

for inclusion in the Geographical

brachio

procurrebat

(Gesam.

Werke,

Appendix IV,

321:5)

to the were

placed after obumbratam by Kepler when he was copying the extract out of the

Report for inclusion in the 1634 Sormmium, p. 9o. 16. The words in the parenthesis were inserted by Kepler after sinubus (Gesamt. Werke, IV, 321:21) when he was copying the extract out of the Report for inclusion in the 1634 Sommium, p. 9o. Kepler must have felt that his description would

be clearer if he explained that the dark gulfs on both sides of the land mass sepa-

rated it "from the continent."

Kepler's Notes on the Geographical Appendix

165

a peak. Opposite it, on the very bright continent of the shores, there was a dark point. Perhaps this indicated a valley, from which material was dumped into the lake and formed the peninsula, as Herodotus speculates about the building up of Egypt.!? Or are these the traces of some Nero, digging through the isthmus,!? or of Cleombrotus fortifying the peninsula with a rampart against the army of some Xerxes? 19

The foregoing 1s taken from my Report, published at Frankfurt in IÓ1I.

Among the observations of September 22, 1622, I find a similar description of what was undoubtedly the same spot. For once more the moon was waning, with the line of separation cutting the small horn off the moon's western edge. I quote: To the west of the moon's line of separation (understand that this was a curved or elliptical line) a sort of shore and high, winding bank was observed casting its shadow into a sea, so to say (toward that horn of the moon from which sunlight had already departed). For in the

parts of this sea beyond the shadow, the latter was followed by light in the middle of the inlet, and the light continued from there right up to the line of separation.

A little toward

the south there was, as it

were, a brilliant isthmus, yet on the bright bank a dark point stood

out. On the other hand, beyond it in the sea a bright mountain was

visible. The horns of that bright bank stretched out like promontories. Where the line of separation passed through the sea, it was, so to say,

interrupted by the lower horn; within the horn it returned to its own (elliptical or curved) line, going on through another spot.

This was from an entry for September 22, 1622. But it is a pleasure also to copy out a whole observation, from which some details

were excerpted in the foregoing "Phenomena." It adds information

17. "Egypt . . . is land acquired by the Egyptians as a gift from the river .... Between the mountains which I said lie above the city of Memphis there once was

a gulf of the sea, it seemed to me... . For, rivers have built these lands up" (Herodotus, 11.5, 10). 18. See fn. 9, above. 19. “The same night the land army of the Persians was marching toward the Peloponnesus. Yet everything possible had been done to prevent the Persians from invading by land. For as soon as the Peloponnesians had learned that Leonidas and

his men had died at Thermopylae, they came together out of their cities and took up a position at the Isthmus under the command of Cleombrotus, son of Anaxandridas and brother of Leonidas. Having encamped in the Isthmus and demolished the Scironian Road, they then decided to build a wall across the Isthmus.

Since there were many tens of thousands of them, and every man worked, the job

was finished. Stones, bricks, timbers, and baskets full of sand were utilized, and those who helped toiled without respite at any time, night or day” (Herodotus, VIII.7I).

166

Kepler's Notes on the Geographical Appendix

about many matters, and contains certain rudiments of the letter, the parts of which we are engaged in demonstrating. In the year 1623, on July 17,20 the day being considered as start-

ing 21 at midnight,

I watched the moon from

1 A.M. to 2 A.M., using

Father Niccolo Zucchi’s lenses??? which have a very long range. Most 20. Since this observation

of July

17, 1623, “contains

certain rudiments

of the

letter” from Kepler to Guldin which forms the Geographical Appendix to the Dream, we may safely conclude that Kepler wrote the letter after July 17, 1623. On December 4, 1623, he informed Bernegger that he had decided to append it to

the Dream: “On the basis of observations with my telescope, which I recently acquired, I shall add a wonderful and novel Appendix on the towns and mounds, which are circular in order that the shadow may be followed” (Gesam. Werke, XVIII, 143:25-27). 21. In the Epitome Kepler explained that the day started at various times in various civilizations, for example, at sundown or at sunrise. But “astronomers . . consider either noon or midnight as the beginning,” choosing midnight for some purposes and noon for others (Gesam. Werke, VII, 193:42-194:6). 22. Here Kepler tells us that he used Zucchi's equipment on July 17, 1623. Previ-

ously, on June 1 and February 6 of the same year, he had observed the planets and

the moon with a telescope (Frisch, VII, 632:7; VIII, 884:last line), which presumably was the same instrument. It was utilized also in Kepler's observation of October 14, 1622 (Frisch, VII, 629:3 up). The earliest observations in this series were made on September 22, 1622, when Kepler concentrated on the moonspots (Frisch, VIII, 833:12; Kepler's Note 1 (xxxiv) on the Geographical Appendix).

If Kepler began this series of telescopic observations on September 22, 1622, then

he may have received Zucchi's instrument shortly before that date. Zucchi accom-

panied Cardinal Orsini to Germany

(see Kepler's Geographical Appendix, fn. 5).

But when did Orsini and Zucchi reach Germany? The may be waiting to be dug out of unpublished documents

answer to this question in the Vatican archives.

Cardinal Orsini was designated "special legate of the Holy

See to the emperor

Ferdinand" (J.P. Migne, ed., Encyclopédie tbéologique, 3d series, 31, Dictionnaire des cardinaux, Paris, 1857, col. 447); the accompanying statement, however,

that Orsini was halted by an illness and died “while he was preparing to leave for Germany”

is refuted

by

Alfonso

Chacon,

Vitae

et

res

gestae

pontificum

ro-

manorum et S.R.E. cardinalium, IV, 440 (Rome, 1677). According to this authoritative seventeenth-century compendium of the lives and deeds of the popes and cardinals of the Roman Catholic church, when Pope Gregory XV died on July 8,

1623, Orsini was in Germany and was therefore unable to attend the conclave which elected Pope Urban VIII on August 6, 1623. Moreover, Orsini was in Prague for eight days in the early summer of 1624 (Alois Kroess, Geschichte der böhmischen Provinz der Gesellschaft Jesu, Vienna, 1910-38, II, 127). Did Orsini's

party reach Vienna two years before, so that Zucchi was able to have his gift of a telescope in Kepler's hands at Linz by September 22, 1622? As late as December 4, 1623, Kepler still referred to his telescope as "recently acquired" XVIII, 143:25-26).

Zucchi's gift was not the first telescope owned

instrument, but he made

(Gesam.

(Gesam.

Werke,

by Kepler. In 1612 he had an

few observations with it on account

of its defectiveness

Werke, XVII, 36:109-10). Before acquiring an instrument of his own,

Kepler’s Notes on the Geographical Appendix

167

of the hollows looked round. But in the upper and lower part of the moon they appeared almost elliptical, according as the convex globe vanished from view. Looking like the crescent moon, the shadows of the valleys in certain cases were clearly the result of ellipses turned sideways, so that from this circumstance you would readily recognize the convexity of the moon’s sphere by mere inspection. Interspersed in the lower spotted parts were some bright circles, embracing hollows and shadows within themselves. Yet these circles were few. You would call them swampy or slimy parts of the moon, in which dams had been erected in a circular form,

like wells, to keep

out the water

lying all around. One of these inclined a little toward the upper part of the moon. It clearly looked like a chasm, open a little wider in the middle of its length. There was no clear difference between the rim and the rest of the moon’s body (spotted or swampy) in all the hollows, but there was a continuous and uniform faint light up to the gap

in the shadow. Most of the bigger hollows had in their middle some-

thing resembling circular glass panes in windows; that is, from the depths of each hollow rose a single hill, but not to the height of the

banks outside. These

hills were

pressed down

again in the middle, like

a navel in a swollen belly or (to use a more closely related example) like the craters of Etna, as their shadow indicated. Yet the hollows did

not darken or join one another, but each one was separate. Nevertheless, from the lower part of the line of separation (which was curved

this time) dark little lunes succeeded one another (intersected by one

another, as was explained) in such a way that with their series they looked like a shadowy elliptical arc. And thus, near each other, two dark fissures were formed. From the separation of light and dark they

Kepler made

observations with borrowed

corded in his Report

were

made

(August 3o-September 9, 1610)

(ibid., IV,

318:37-319:2;

with

telescopes. Thus, the observations re-

an instrument

lent to him

for a few

days

by a prelate, who had received it from Galileo

322:31-32).

Other

"instruments

sent

by

the

last

Galileo

himself

were made accessible" to Kepler, but he himself never received a telescope from Galileo

(ibid.,

XVI,

No.

strument

(ib7d., IV, 511-13).

600o:111-12,

257-59).

During

four

weeks

of

October, 1610, Kepler was able to use a telescope owned by Wackher von Wackenfels; but at the end of the month Emperor Rudolph II asked for the inKepler was not very favorably impressed by the early telescopes he had han-

dled. He told a correspondent on December 18, 1610: “I say that there is no great novelty in the invention of the tube with two lenses, because single lenses had

been in use. Even so far as the heavenly bodies are concerned, ever since I have been cultivating astronomy, by employing lenses I have seen more stars more

finely and more distinctly, and the face of the moon more clearly, especially in eclipses” (Gesam. Werke, XVI, No. 600:43-47). But in the Epitome he talked about what a good telescope could do (#b7d., VIT, 511:5). And he had a very high

opinion of Zucchi’s instrument, which

he used in 1623 to measure the apparent

diameter of Mars and the other planets, and to observe the moonspots (ibid., VII, 366:8; Frisch, VII, 592:7-6 up, 593:26-29). He expressed this opinion in his

Shieldbearer of 1625 and in his Admonition of 1629; in a private letter written in the latter year he discussed the shortcomings of various arrangements of tubes and

lenses (Gesam. Werke, XVIII, No. 1103:82-111).

168

Kepler’s Notes on the Geographical Appendix

wound their way into the bright part bending upward. Yet on both sides they were modified, as I said, by bright parts which crossed them

in continuous bands. You might call this a very long valley, which ex-

tends below curving mountains on both sides and covered by them when they are viewed from the side.

is,

as

it were,

This was the observation of July 17, 1623.

These, then, are the observations, these are the axioms, on the basis of which I shall now demonstrate the individual parts of the letter which are marked by a number.”” 2. The hollows chiefly occupy the spots, not the bright parts.

This statement is connected with xxiv, and is itself derived from in-

spection.

3. [he spotted parts are lower than the bright parts, as 1s de-

duced in xir. 4, 5. Completely black spots are seas, I conclude in xxi; less thoroughly black spots are swamps, I conclude in xxi and xxm. 6. If they measure the areas, there must be agreement among them; you have this agreement in xxxii.

7. Striving for a definite goal is the mark of a rational mind,

which also indulges in sport for the sake of passing the time. But works done for fun should not be assigned to the same order of magnitude as those intended for the purpose of self-preservation. These works, however, are so very large that at a distance of 50,000 miles they do not escape our senses. 8. Some of the hollows are surrounded on the outside by a rampart. Ihe hollows are sunken down in the spotted regions, which are turned black by the prevailing wetness. From these facts I infer that the rampart was erected against the water outside. But the technique of getting rid of the water which was inside the rampart was taught to those moon-dwellers, I suppose, by our Dutchmen.

In my Conversation, page 17, I made the opposite surmise, namely,

that ditches are dug, perhaps even for the purpose of drawing water up out of the depths.”* But at that time I had not yet ob-

served that the hollows are in the spotted, not the bright, parts. 9. Ihe sun is undeniably their most determined

23. In the 1634 Sommium

enemy.

those parts of Kepler's letter to Guldin

In my

which

are

annotated are marked by letters, beginning with “a” and ending with “pp.” These letters were changed by Frisch to numbers, from 1 to 38, and the word literis in the 1634 Somnium was replaced by numeris (Frisch, VIII, 73:2). The present translation follows Frisch in these details for the convenience of the reader. 24. Gesam. Werke, IV, 299:16-17, with et replaced by etiam, and in by e.

Kepler’s Notes on the Geographical Appendix

169

Conversation I wrote about this subject as follows: “Their day is as long as fifteen of our days, and they feel unbearable heat. Perhaps °° they lack stone for constructing shelters against the sun. But on the other hand, maybe * their soil is sticky, like our ?

clay. Therefore they have used the following method of building. Digging up huge fields, they carry the earth out in a circle and spread it around.”® In this way they may hide deep down in the

shade behind the mounds which they have heaped up. They walk around on the inside, following the shadow according to the sun’s

motion. This is for them, so to speak, a sort °° of underground

city, their homes being the very numerous caves cut into that circular embankment. Their cultivated fields and pasture lands are in the middle, so that in their flight from the sun they are not forced

to go too far*® away from their farms.” ** This was what I thought at that time. I had not yet discovered that hills rise up out

of the hollows, with the middle pushed down like a navel, and that the surrounding rampart is on the outside of some hollows. For, I reasoned, they acquire extensive shade more easily not only by burrowing a pit but also by piling up the excavated matter on the outside against the sun. What I thought they had to do for this reason of doubtful validity, is done in that very way, as vision and the telescope now testify; whether against the sun, as is indicated by the present Note 9, or against the water, as by Note 8, or against both, must be left undecided. 10. Once a comparison is instituted between the populations of the moon and of the earth, the judgment about similar things is the same. Since we see that the moon’s spotted parts are civilized, we shall assign to the surrounding rough and mountainous regions wild and savage bands of thieves. Let these be the enemies of the more civilized people, who build their fortifications against them. But in this connection recall the observation in xxxiv,®? which can 25. Here Kepler replaced fortasse by forte.

26. Here Kepler replaced forsan by fortassts. 27. Here Kepler inserted nostrae for the sake of clarity.

28. Here Kepler omitted the words which he had just quoted in his Note the Geographical Appendix (see above, fn. 24). 29. Here Kepler omitted quaedam. 30. Here Kepler reversed the word order of longius non. 31. Gesam. Werke, IV, 299:12-22; Rosen, Kepler's Conversation, p. 28.

8 on

32. Kepler refers to the closing words of the excerpt from his Report given in his Note 1 (xxxiv) on the Geographical Appendix to the Dream.

170

Kepler’s Notes on the Geographical Appendix

be explained in no other way than as attack. 11. The hollows have the form of around a center. This, therefore, must something for measuring the distances

a fortification against hostile a circle. A circle is described be visible and equipped with to the circumference.

12. With such long distances, equality can be obtained

with a rope.

only

13. Because the diameters of the hollows are unequal. 14. At a single glance my instrument took in 12’ of the moon’s 30’. Its diameter is 400 German miles long.?? Therefore my instrument covered about 160 miles.** But the diameter of this spot is

about one-sixteenth of the capacity of my instrument. Hence it extends ten German miles, and consequently its radius is five.??

r5. Do not say that a circle having a radius of five miles can be described with a continuous swing of one leg of a compass, unless a draftsman at least twenty miles tall is available. 16. But neither does a single rope suffice, with its outer end to be drawn around the stake to which it is tied. For of its own weight the rope will sag down to the ground, and get caught in the hills

and rocks and other things which make the surface of the ground

uneven. What remains, therefore, is that on the circle under construction, separate points, distant from one another by an interval which is not too great for one point to be seen from another, are marked off by separate ropes, tied to the same stake. However, the surveyor must proceed from the stake to the circumference with a loaded wagon in order to have rope long enough for five miles.

17. From xxix we gather that the individuals of the lunar nation

are not to be matched in size of body with the lunar mountains, but from xxxi that they are a numerous population. Therefore, since the visual evidence testifies to their huge works, they must accomplish by their numbers what the size of their bodies cannot do. Let us take as various examples the tower of Babel, the pyramids

33. At the end of his Note 207 on the Dream Kepler put the moon’s diameter at “about five hundred miles,” which is shown in fn. 338 to Kepler’s Notes on the Dream to be a convenient approximation of 430 (German) miles. Hence his approximation here in his Note 14 on the Geographical Appendix is somewhat closer to the figure he actually accepted, which is well below the modern determination (about 2,160 English miles). 34. 12:30 = 160:400.

35. 1/16 X 160 = 10 X 1/2

= 5 German miles.

Kepler's Notes on the Geographical Appendix

171

of Egypt, the very long road paved with stone in the province of Peru,?? and the wall protecting the Chinese from the Tartars.

18. In that big hollow which has a diameter of ten German

miles, a good part of the diameter is taken up by the gap between

the rim and the hill rising up within. Anybody who says that the

gap 1s not less than one German mile does not deny that it may be

somewhat greater, as vision testifies. But on this basis estimate the size of their bodies. Even though it is not to be compared with their mountains, it is still much greater than the size of our bodies, as 1s indicated by their works, which far surpass ours in number. I

ventured to say this plainly in my Optics, page 250, solely on the

basis of a comparison of the lunar mountains with ours, in the following words: “Plutarch correctly says that the moon is a body like the earth, uneven and mountainous, its mountains being even higher in proportion to its globe than are the mountains of the earth in proportion to its globe. Let us, too, jest ?* with Plutarch. It happens among us that men and beasts agree with the nature of their land or province. So on the moon there will be living creatures of a much greater bodily build and toughness of constitution than ours," ?* and so forth. I9. Since the ditches are visible (according to xxv) and these are artificial (according to xxvii), they cannot be constructed by any method other than by excavating the material. Now the moon-

dwellers find nowhere to dispose of it in the diggings proper. It

cannot be that nothing is made from the material, just as art cannot

make anything material out of nothing.

20. Let this statement hold true of those hollows which are seen

not to have an outer hollow guarded by a bright rim, as was said in xxx and in the observation of the year 1623 after xxxiv. The presence of the excavated

material in the interior, however,

follows

36. Kepler may have read about the royal road of the Incas in Antonio de Her-

rera

(1559-1625).

His

Description

of tbe

West

Indies

(Madrid,

1601),

as trans-

lated from Spanish into Latin by Kaspar van Baerle (Amsterdam, 1622; Frankfurt, 1624, as Pt. 12 of Theodore de Bry's America) said: “Through the mountains two

roads wind. The first is called ‘the Incas,’ and it crosses the Andes from Pasto [in present-day Colombia] to Chile. It is nine hundred leagues long, and is paved with stone to a width of twenty-five feet" (Ch. 16, fol. 22v; Descripcion de las Indias ocidentales, p. 46). 37. The word after jocemur should be quia (Gesam. Werke, II, 220:6), correct-

ing the misprint qui in the 1634 Sommium (p. 94). 38. Gesam.

Werke,

Il, 220:3-9.

172

Kepler s Notes on tbe Geographical Appendix

from the appearance of the hills rising up out of the bottom, and from the metaphysical axiom that nothing happens without a cause. But here a height is created in the middle of the hollow. Therefore it has a cause. Yet there is no more probable a cause than the excavation of the material which had previously filled the nearby ditch visible all around. Nor can another cause be readily devised. 21. It follows that in the hollows surrounded by a bright rim, a part of the material is carried outside. For this is what makes that very rim. I would say “all the material,” if the ditch were empty, and if the hill did not rise up from its bottom. Therefore, where the hill is inside, a part of the material is believed also to be carried inside. 22. In these towns there is a double rampart because, as I said, the outer rim is the first rampart. But what is carried inside becomes the rampart not for the ditch outside (which 1s not threatened by any danger from within) but for the gap in the middle of the hill’s navel.

23. Ihe great depth of the ditch is attested by the abundance of

the excavated material. For from this is constructed not only the outer rampart rising on all sides to a remarkable height, but also the hill within, which is likewise quite conspicuous.

24. This is based on the observation in xxvii and on the method of

construction, which was previously deduced. For on the assumptions that all the places are everywhere equidistant from the stake, and that the ditch continues without interruption from one chosen place to another, the ditch will become a perfect circle, and there-

fore so will the outer and inner ramparts, as I point out in Note 25.

For on the assumption that the creatures are to a certain extent endowed with reason, for them there 1s nothing incongruous in this equality of the ropes stretched in all directions.

[25. Missing.

26. Ihe mind does nothing in vain. But to excavate the top of the hill inside as though it were a navel seems unnecessary. For from the very accumulation of the material removed from the inner ditch, a mound rises up high and leaves a gap on the other

side in the center, as I point out in Note 27. [27. Missing. |

28. This, too, is recommended to us by our terrestrial mechanics

Kepler's Notes on the Geographical Appendix

173

and architecture. For it is one of the principal rules, since it also affects the main part of the operations, especially in laying the

foundations. 29. According to xxi, there are swamps on the moon. Hence

our agriculture supplies everything else for our conclusion, namely, that if you surround a swampy area with a deep ditch, water flows down into it both from the outside and from the enclosed area.

30. If the drainage of the area does not go deep enough, material

taken from the ditch and thrown onto the area will elevate the terrain and keep it from being touched by the surface of the water.

31. In those affairs which are managed rationally, it is the regular practice that nothing is done without a purpose. In this instance

rational creatures, whose existence is taken for granted in the letter, have constructed a ditch fit to receive water, and a circular ditch at that. What would be the purpose of making water travel in a circle if not to sail on it? 32. Ihe great length of the very hot day makes it likely that the water dries up almost every day. Hence, when this happens, the ditch has another use: they walk around on the bottom of it.

33. [heir purpose in walking around is to keep cool. This is surely no mere exercise or sport. These works—the sort of conjecture we accepted among the axioms above—are much too big for that. On the contrary, their walking around is the direst necessity;

they must protect themselves from the strength of the sun by the

shadow of the rampart down at the bottom. To enable them to do this at all times, the ditch must be circular, and they must change their position as the sun also changes its. They do this either by sailing without exerting themselves or with the greater inconvenience of a journey on foot.

34. For those who are in the ditch have the hill on one side and

the outer rampart on the other. Therefore if the sun is on the same side as the outer rampart, the latter provides shade for them.

35. But if for them or those opposite them the sun is on the same

side as the hill, those who are in the ditch hide in the shade behind the hill or inside rampart.

36. For those who are in the navel of the hill receive no shade

from the outside rampart. But from the inside rampart they do receive shade. And they receive it without becoming exhausted, because down at the bottom around the center the place is narrow,

174

Kepler s Notes on the Geographical Appendix

and by making a short trip they cross over from the areas scorched by the sun to the shaded areas. Or if the rampart casts no shadow at noon when the sun is overhead, it stands to reason that they have caves dug into the steep rampart, in which they hide and avoid the noonday sun.

[37, 38. Missing.]

In this way, therefore, I believe that everything in the letter has

been proved, as I promised at [Note] number 37. And this has been done by various and

numerous

axioms,

as I promised

at

[Note]

number 38. I have now said enough about this Letter. By terminat-

ing it, I bring this book of mine to a close, and send the reader on to become acquainted with the following work by an ancient author.?? 39. Plutarch's Moon, as translated from Greek into Latin by Kepler, followed at this point in the 1634 Sommnium.

Appendixes Bibhography Index

Appendix A JACOB BARTSCH

Jacob

Bartsch

was born in 1600 in Luban

what is now southwestern

Poland. Some

(formerly

information

Lauban)

in

about his educa-

tion may be gleaned from his Astronomical Use of the Planispbere, in

the preface of which he expresses his gratitude to his teachers. The first of these whom he mentions taught him the astrolabe: its “construction and use were demonstrated five and more years ago [Bartsch

dedicated the Planisphere on January 1, 1624, new style] by the illus-

trious gentleman Sarcephalus, the mathematician and Wroclaw, my mentor, who is to be cherished as though

my professor.” 1 This last expression

the instruction rangement.

given

to Bartsch

(praeceptoris loco)

by

Sarcephalus

In 1601 the City Council of Wroclaw

was

by

librarian of he had been

implies that private

ar-

(then called Breslau) had ap-

pointed Christopher Sarcephalus librarian of the Magdaleneum, a municipal school.” The mathematician-librarian’s real German surname was Hauptfleisch. This he dropped, in keeping with the contemporary humanist fashion, and adopted instead the equivalent Greek

form Sarcephalus (fleshy head). Kepler sent him a copy of the first part of the Ephemerides, presumably because Sarcephalus was himself the author

of many

works

brarian of the Magdaleneum the age of 66.4

of the

same

character.?

He

until he died on September

remained

li-

20, 1633, at

1. Bartsch, Usus astronomicus planisphaerü stellatt, Strasbourg, 1624, p. 2; 2d ed., Nuremberg, 1661, entitled Planisphaerium stellatum, pp. 10-11. The cost of printing the 1624 edition was paid by Jacob von Heyden, who engraved Bartsch's

drawings for this volume, and also the portrait of Kepler for Bernegger.

2. Johann Heinrich Zedler, Grosses vollstandiges universal Lexicon (Leipzig and Halle, 1732-50; now being reissued, Graz: Akademische Druck- und Verlagsanstalt), 34: col. 72. 3. Gesam. Werke, XVII, 417:29-30; Sarcephalus’ name was omitted from the Index of Persons, ibid., 534. 4. Zeitschrift des Vereins für Geschichte und Alterthum Schlesiens (Breslau, 1876), 13:218.

177

178

Appendix A

In 1619 Bartsch paid a visit to his home in Luban. For he later said that in 1627 he had “not seen his parents for eight years.” ? In 1620 he

composed and published a poem at Wroclaw to celebrate the arrival there of Frederick V of Bohemia, the Protestant “Winter King.” Presumably it was for this bizarre dithyrambic mixture of Latin and German that Bartsch was crowned “Royal Poet Laureate,” a title to which he clung long after the Winter King had lost his throne to the Catholic Counter-Reformation. Frederick was scheduled to pass through the ceremonial gate, which Wroclaw, the capital of Silesia, had erected in his honor, on Sunday afternoon, February 23, 1620, at 3:53 P.M. The horoscope of that moment was cast by Bartsch, who was addicted to astrology.

In the preface to his Planisphere Bartsch saluted Philip Müller, “the

most excellent professor of mathematics at Leipzig University, my teacher and mentor. . . . I attended his public lectures in the second part of his [course on] astronomy at Leipzig, three and more years ago." 9 Bartsch placed these lectures in 1620, when he listed the authorities from whose writings or oral instruction he had benefited.’ He likewise said, in dedicating Kepler's Admonition to Müller on October

5/15, 1629: "Nine years ago you were my first teacher of the science

[of astronomy] in a university." 5 His attendance at Müller's lectures, Bartsch stated, “was interrupted, to my regret, by my departure." ? From Leipzig Bartsch transferred to the University of Strasbourg, where he enrolled as a student of medicine in 1621.1? [n the following year he published a book about the

mock suns and rainbows which had been seen at Strasbourg on January 25, 1622 (Julian calendar or old style; according to the Gregorian

calendar or new style, the unusual phenomena were seen on February 4,

1622 ).!! In that same year his name appears among the candidates for

the master's or doctor's degree in philosophy.!?

The attainment of the former distinction did not take him very long, since in May, 1625, he held a master's degree in philosophy. He so indi-

cated in signing the dedication of a discussion of spotted which he was the respondent. This discussion was proposed 5. 6. 7. 8.

bo

Nova Kepleriana, 4, 94:12 up. Ed. 1624, p. 3; ed. 1661, p. 13. Bartsch, Planisphere, ed. 1624, fol. Agr; ed. 1661, p. 3. Frisch, VII, 590:4-5. . Planisphere, ed. 1624, p. 3; ed. 1661, p. 13. 10. Matrikeln . . . Strassburg, I, 6. 11. Himmlische zeiterinnernde Wunder-Sonn-und-Weck

fever in by Mel-

the dedication is dated February 15, old style). 12. Matrikeln

. . . Strassburg, I, 519.

Uhr

(Strasbourg,

1622;

Jacob Bartsch

179

chior Sebisch, Jr. (1578-1674), the extremely energetic professor of medicine. Sebisch also presided over another disputation in which Bartsch was the respondent. This was printed as the ninth (Strasbourg, 1623) in the series of Medical Exercises published by Sebisch, and was dedicated by Bartsch to two medical practitioners in Wroclaw. Also in 1623, on October 13/23, and again with Sebisch presiding, Bartsch defended a dissertation entitled the Sixth of the Medical Exercises Based on Fernel: Diseases and the General Differences among Them, the Exercise Consisting of Tables, Aphorisms, and Questions Drawn from the First Ten Chapters of Book I of Fernel’s Pathology. A group of ten such medical exercises based on Jean Fernel (1495-1558), the greatest physiologist of the sixteenth century, was published by Bartsch (Strasbourg, 1622-25), with the other medical professor, Johann Rudolph Salzmann, Sr. (1574-1656), presiding over some of them.? A compact summary of Bartsch’s medical publications at Strasbourg has been provided by a historian of medicine and of institutions giving medical instruction at Strasbourg." Jacob

Bartsch's

brother

Frederick

matriculated

faculty of Strasbourg University on June

in

the

theological

7, 1623.15 Working

to-

gether, the two Bartsch brothers in 1624 constructed a celestial globe supported by four legs. The next year they jointly published a description of the device,!® and sent copies of this description

to the leading

astronomers. It was dedicated to three scientists, including Philip Müller and Kepler. Jacob Bartsch's letter of transmittal to the latter, sent at the end of April,

1625, was the first contact between

the two

men. In this letter Bartsch announced that he was planning to leave in June for Padua “to press on further with the continuation of my principal study, medicine, because everybody knows that it flourishes most

there." Asking for globe, he added: “I in person.” !* Late Tiibingen.18 From him:

and

Kepler's judgment of his work on the celestial should like nothing better than to hear it from you in June, and early in July, 1625, Kepler visited there Wilhelm Schickard subsequently wrote to

“Shortly after you left, Bartsch came to stay with me in the hope

desire of still finding

you

at my

house."!?

Although

Bartsch

13. Otto, Lexikon, III, 605. 14. Friedrich Wieger, Geschichte der Medicin und ihrer Lebranstalten in Strassburg (Strasbourg, 1885), p. 76. 15. Matrikeln . . . Strassburg, I, 594. 16. Novus globus caelestis (Strasbourg, 1625; dated March 15, 1625, fol. Bav). 17. Gesam. Werke, XVIII, 232:35-36, 43-44. 18. Frisch, VII, 638:16 up, 9 up. 19. Gesam. Werke, XVIII, 245:5-6; an account of Schickard (1592-1635) and

180

Appendix A

missed Kepler at Tübingen, he managed to catch up with him a month later.?? “That happened to me in Ulm, I am delighted to say, three

years ago,” Bartsch wrote to Kepler in 1628; “at that time I was on my

way to Padua in Italy. While passing through, I had a brief, but welcome, opportunity to talk to you." ?! Another scholar with whom Bartsch had an opportunity to talk at

that time

was

Julius Schiller

friendly, and Bartsch astronomical work.

helped

of Augsburg.

Schiller with

The

two

the closing

men

section

became

of his

On September 15, 1625, Bartsch inscribed a hearty greeting to Padua

and its medical school in the official register of the German students of the arts there.?? When Bartsch returned to Germany from Padua, he went back to Augsburg, where he rendered further assistance to Schiller. In the lat-

ter's Christian Starry Heaven, of which two different editions appeared at Augsburg in 1627, Bartsch was responsible for the tables and related drawings.?? Schiller died about Easter, 1627, before the work

was finished, and Bartsch published an appropriate commemorative

tice at Augsburg on May

no-

14, 1627.?* In his Rudolpbine Tables, Kepler

referred to “Jacob Bartsch of Lusatia, a diligent young man, who some time ago acquired an excellent reputation for his good work in connection with the celestial globe. . . . From Augsburg he recently sent to me in Ulm a beautiful engraving detached from Schiller's Christian

Starry Heaven, the publication of which he is expediting in accordance with the author's last will and testament." 2° While Bartsch was thus occupied in Augsburg,

from Kepler a copy

of the latter's Rudolphine

he received as a gift

Tables

(Ulm,

1627),

"still hot from the press," as Bartsch put it. In an accompanying message Kepler asked Bartsch to read the volume carefully and to answer some questions. But Bartsch could only leaf through the book before his publications will be found in Christian Friedrich Schnurrer, Biographische und litterarische Nachrichten von ehmaligen Lehrern der hebräischen Litteratur in Tübingen (Ulm, 1792), pp. 160-225. 20. Frisch, VII, 638:9 up, 639: 14-15. 21. Nova Kepleriana, 4, 93: 17-18.

22. Vol. 465 of the old university records, as I was kindly informed

by the

keeper of those records, Dr. Lucia Rossetti. 23. Coelum stellatum Christianum, pp. 126-34. Schickard contributed the Arabic names of the stars (p. 27). 24. Ihe Swiss Federal Astronomical Observatory in Zurich courteously sent me

a photocopy of Bartsch’s broadside. 25. Pt. 4, p. 118 (not of the Precepts, but of the Tables proper, with their separate pagination).

Jacob

Bartsch

181

he departed from Augsburg for Leipzig.?9 There he left his copy of

the Rudolpbine Tables for a while with Müller, and went on to Luban, the home of his parents whom, we recall, he had not seen for eight

years

(1619-27).

At the beginning

of 1628 his copy

of the Rz-

dolpbine Tables was returned, and he instituted a series of extensive

calculations, which

took him more than six months.

The first product

of these calculations was his Strasbourg Observatory or New Tycbonico-Keplerian Epbemeris of tbe Motions in tbe Heavens for 1629, Carefully Computed on tbe Basis of tbe Rudolphine Tables in Accordance with Tycho Brabes Observations, as Corrected, and Johannes Kepler's New Physical Hypotheses (Leipzig, 1629).

Bartsch was eager to make some suggestions to Kepler about the computation and arrangement of ephemerides. “From my country I sent letters addressed to you,” Bartsch informed Kepler, “twice to Prague and once to Ulm. In other places I did not neglect the opportunity to ask questions everywhere. But from Prague one letter came back to me with the information that you were away, and the other with the news that you had left. From Ulm I received nothing. Nor did I know where in the world you were until a few days ago.” Having been told by Miiller that Kepler had transferred his base of operations to Silesia, Bartsch resorted to two methods of communicating with him. Not only did he send Kepler a private letter, but he also ad-

dressed to him one of the prefaces of his own ephemeris for 1629. It is

from Bartsch’s preface to Kepler that we have just been quoting.?' Bartsch’s preface, which took the form of an open letter, was an-

swered by Kepler's equally open Reply to Jacob Bartsch’s Letter (Zagan, 1629). Kepler dated his Reply November 6, 1629.7? But “1629” was a slip of Kepler's pen for “1628.” °° Had Kepler written

the year as an Arabic numeral, the error might be imputed to his typesetter. But he used the Roman style “MDCXXIX,” which a compositor would hardly have set in place of “MDCXXVIII.” In letters written in

1629 on April 3o and July 12/22, both Bartsch and Kepler referred to printed copies of the Reply.?? In the Reply itself, where Kepler felt

obliged to recount his recent comings and goings, he said: "I arrived at Frankfurt for the book fair in the month of September last year, bring-

ing the Rudolphine Tables to be shown publicly and to be inserted in the catalogue." ?! In this context "last year" refers to 1627, the work 26. 27. 28. 29. 3o. 31.

Frisch, VII, 586:3, 590:7. Nova Kepleriana, 4, 93:16-13 up. Frisch, VII, 585:last two lines. As was demonstrated in Caspar, Bibliographia Kepleriana, p. 101. Gesam. Werke, XVIII, No. 1107:12-13, NO. 1111:124-26. Frisch, VII, 581:25-27.

182

Appendix A

of printing the Rudolphine Tables having gone on from late in 1626 to September, 1627.22 Moreover in the Reply Kepler said that he hoped to have another book printed in time “for the Frankfurt

book

fair in

the autumn of 1629.” 33 Hence it is clear that in the Reply Kepler was writing on November

6, 1628, about the ephemeris

for

1629. In these

circumstances his misdating of the Reply is readily understandable, but

it must be corrected

lest we fail to realize the promptness

of the Re-

ply: Bartsch's preface addressed to Kepler was answered in less than ten weeks.

Kepler began the Reply by telling Bartsch: "You talked to me in a

public letter about certain subjects. . . . I explained my opinion about them to you face to face when you visited me recently. Nevertheless, because you wrote publicly and many people are interested to know what we decided, I shall answer your statements publicly as well." ®*

Recalling the publication of his earlier Ephemerides, which had covered the years 1617 through 1620, Kepler spoke of the continuation for which

“you, my

dear Bartsch,

offered

me

your

cooperation

pleasure

that at our

long ago in the letter that you sent from Augsburg to Ulm, and now in

your public letter. I publicly acknowledge with recent meeting I accepted your cooperation.” °°

Ihis meeting probably took place at Zagan in Silesia, the city to which Kepler had moved on July 26, 1628.9 About a month later

Bartsch was notified by Müller that Kepler's new headquarters were located in “the region [Silesia] adjoining his native land [Lusatia].” 3? In his preface addressed to Kepler, Bartsch said that they would meet soon in Silesia. Then on November 6 Kepler referred to that meeting as "recent." Hence we may safely assume that the Kepler-Bartsch reunion at Zagan occurred in September or October, 1628.

In his Reply, it will be recalled, Kepler mentioned the letter which

Bartsch had sent from Augsburg to Kepler in Ulm. This letter has disappeared. In fact, only one private letter addressed by Bartsch to Kepler has survived, and that is the above-mentioned message of April,

1625, transmitting

globe.

the description

of the Bartsch

brothers’

celestial

An ephemeris for 1629 had been partially computed by Kepler. But

he was 32. 33. 34. 35.

willing to incorporate

Bartsch's

Caspar, Bibliographia Kepleriana, p. 97. Frisch, VII, 584:23-22 up. Ibid., $81:15-19. Ibid., 584:21-19 up.

36. Ibid., 582:4-3 up; VIII, 910:9.

37. Ibid., VII, 590:8-9.

instead:

"Since

yours

has al-

Jacob Bartsch

183

ready been issued, I prefer to have it reprinted, as we agreed.” 38 Kep-

ler closed his Reply on a note of firm resolve: “While the storms

[of

war] rage and threaten public destruction, we can do no better than to

drop the anchor of our peaceful studies in the depths of eternity.” °° In dedicating the Ephemerides for 1629-36 to Wallenstein, duke of Friedland,

Kepler

said:

“The

first happy

outcome

of my

moving

to

Silesia as a result of your generosity, O famous duke, was that in neighboring Lusatia I found a brilliant and assiduous collaborator in continuing the work on the Ephemerides.” *© Making a strenuous effort to finish a part of the Ephemerides in time for the next autumn book fair, on April 3o, 1629, Bartsch reported to Müller from Luban: “I am compelled, together with my brother [Frederick], to press on with the calculations night and day, and thus I can't have any time for

other things. . . . I did not want to refuse to collaborate with Kepler.

Besides other promises, which are far from negligible, he pays no small sum for the work." *! Jacob Bartsch may therefore be described as an employee

of Kepler's, and a collaborator with

him, but he was

not a

pupil of Kepler. After an absence of nearly four and a half years (June, 1625— November, 1629), Bartsch returned to Strasbourg. There on February 17, 1630, he satisfactorily conducted a disputation on various cases in Hippocrates’ Diseases, Book 4.42 Then, two weeks later, "Melchior Sebisch, presiding over a great throng of learned men, awarded Bartsch the insignia of the M.D. degree on the very morning” of the day he

was married, March 2, 1630.*?

Bartsch married Kepler’s daughter Susanna, who was born at Prague

on July 9, 1602.44 Nothing is known

about her childhood. But when

she was fifteen years old, Kepler reported the receipt of a “letter from

my son-in-law [Philip Ehem] informing me about the death of his wife

[Regina], who was my stepdaughter. This was a most grievous loss to him and to their three children. By all that is sacred he pleaded with me to let him have my daughter [Susanna], now fifteen years old, to

comfort his children, deprived of their mother, and to take some sort 38. Ibid., 584:15-14 up. 39. Ibid., 585:6-3 up.

40. Ephemerides, fol. bbbzr-v; Frisch, VII, 567:13-15. 41. Gesam.

Werke, XVIII, No. 1107:11-12, 22-24.

42. Matrikeln . . . Strassburg,

II, 126. What

was

then

regarded

as Bk. 4 of

Diseases is now thought to be part of another work, which may not even have emanated from the Hippocratic school, let alone from Hippocrates himself. 43. Gesam. Werke, XVIII, 422:15-17. Sebisch had contributed a laudatory poem

to Bartsch’s Planisphere (ed. 1624, fol. A4v). 44. Frisch, VIII, 745:3 up.

184

Appendix A

of care of the house for a short time, because

he had to be away

account of his work. Therefore in the month of October [1617]

on

I set

out with my daughter on a very slow trip up the Danube to Regensburg. . . . [left my daughter near Regensburg in Walderbach," where Philip Ehem lived.*? Other business took Kepler farther on horseback. But in December, 1617, on his way home to Linz, Kepler passed

through Walderbach, where he spent more than a week.*° When

Susanna

was

only

seventeen

years

old,

Kepler

wrote

to

a

friend that by stimulating interest in his Harmonics and increasing its

sales, “you will help me accumulate a dowry for my daughter. Even though her father is against it, as the years slip by with their effects hidden, she has been inviting and seeking marriage for some time, unless my suspicion is mistaken." 47 For almost a decade thereafter we lose sight of Susanna. Then she may have experienced some unpleasantness about which we are poorly informed. While Kepler was supervising the printing of his Rı-

dolphine Tables in Ulm, he had occupied a house provided for him by an old friend, Dr. Gregor Horst (1578-1636). From Ulm, where he

was the town physician, Dr. Horst wrote to Kepler on March 12/22, 1628: “That rumor about your daughter's being dismissed has spread among us, too. I am happy to learn from you yourself what I wanted to find out from Mr. Mögling by letter. Whether she is still hiding in Butzbach or has gone to Durlach, I don't know, because I haven't had any letter from her thus far." 48 Daniel Mógling had been appointed personal physician to Philip of Hesse-Butzbach in 1621, and also was assigned mathematical tasks as well as work connected with the Landgrave's astronomical observa-

tions; he remained in Philip's service until 1635.49 In a letter written from Butzbach on December 27, 1627, Mógling referred to Susanna as "being with us now" (“ietzo bei uns ist”).5° By the expression “with us" Mógling meant, not in his home, but at the court of the Landgrave. That Susanna remained there only a short time is made clear by the

Landgrave's remark early in 1630 that Susanna "once lived at our court for a little while." 91

45. Gesam. Werke, XVII, 254:14-21, 27-28; Stóckl (ed.), Kepler-Festschrift, pp. 127-28. 46. Ibid., 254:40-41; Frisch, VII, 620:27-24 up. 47. Gesam. Werke, XVII, 383:323-26. 48. Ibid., XVIII, 340: 11-14. 49. Walther, Arch. f. bess. Gesch. u. Alt., 11:371-72. 5o. Vienna, National Library, MS. 9737, fol. 8. An excerpt from this manuscript was given to me by Dr. Franz Hammer, whom I wish to thank for his courtesv. $1. Gesam. Werke, XVIII, 425:6-7.

Jacob Bartsch

185

Some three weeks after Dr. Horst wrote from Ulm, Kepler told his friend, Bernegger, “... my unmarried daughter Susanna... is

going to be in the women’s quarters at Durlach.” 5? Then, in a legal document dated June 18, 1628, Kepler referred to “my daughter now

working at Durlach in the women’s quarters of the noble Margrave” of Baden-Durlach, who had his castle at Durlach.53 Bernegger, whom Kepler informed about Susanna’s employment at Durlach, was professor of history at Strasbourg University. Since Strasbourg is less than fifty miles from Durlach, Kepler appealed to

Bernegger on April 10, 1629: “Be a father to my marriageable daughter.” ?* This role delighted Bernegger, who wrote to Kepler on July 5, 1629: “You have a letter here from your daughter, which she recently sent from Durlach for me to take care of. For we have become such good friends,

with

your

kind

permission,

that

we

exchange

letters

con-

stantly, as lovers usually do. And indeed I love her dearly, not only

because she is tain marvelous A widower Kepler wrote

your daughter, but also because her letters evince a cercharm and intelligence beyond her sex." 5? having been mentioned as a possible husband for Susanna, to Bernegger that he had his eye on Bartsch:

He is my neighbor and my collaborator in the computations. He is still a bachelor, having set aside his plans for marriage while watching the outcome of the Reformation in Lusatia. The situation in the little province is very dangerous. . . . I ask you, since you knew him at Strasbourg, how he lived and how much he spent. What hope is there

in his hope of a professorship at Strasbourg in the event of a disaster

in Lusatia? I dislike one thing about him, that he anchors his studies in

astrology, and despises medicine. If you can write me the kind of thing which you yourself think will satisfy me, please write to him.

First, oppose his plan to set medicine aside and on mathematics. Then build up his hope that, he can live comfortably in Strasbourg, if that Then add, as the main item, that he should

to fall back exclusively assisted by my support, is how things turn out. make an open advance,

already suggested in his public letter, to seek my daughter in marriage even from you, as though you were her guardian.5®

52. Ibid., 354:15-16.

53. Stöckl (ed.), Kepler-Festschrift, pp. 103-4. 54. Gesam.

Werke,

XVIII, No.

1105:8-9. In 1620 Kepler

had sent a portrait of

himself to Bernegger (ibid., No. 893:7-8). On January 1, 1627, as an expression of his esteem for Kepler, Bernegger hung the portrait in the library of Strasbourg University, and a little later wrote to Kepler:

day might rather see you in person”

“Would

that those who

(ibid., 281:48-49). The

present volume reproduces this portrait of Kepler. 55. Gesam. Werke, XVIII, No. 1109:9-13. 56. Ibid., No. 1105:14-27.

see it every

frontispiece of the

186

Appendix A m5

In referring to “the event of a disaster in Lusatia," 9 Kepler meant that the Catholic Counter-Reformation might triumph there. If it did, Bartsch would either have to accept compulsory conversion to Catholicism or leave Lusatia. As a sincere Protestant, Bartsch would, of

course,

never

submit

to the former

would be available to him Kepler put it.

alternative.

“in the event

Hence

only

flight

of a disaster in Lusatia,"

as

Before we leave Kepler's private letter of April 10, 1629, to Bernegger, we should recall that it refers to Bartsch's having "already sug-

gested in his public letter" that he wanted to marry Susanna. As the anxious father of a marriageable daughter, Kepler so interpreted Bartsch's remark that since they were going to meet soon in Silesia, he would “for the present omit other private matters, which... I shall hereafter explain better when we are face to face.” °° About a month after Kepler asked Bernegger to help him acquire Bartsch as a son-in-law, the Strasbourg professor complied. Answering

Kepler on May 14, 1629, Bernegger said: “Please read the enclosed letter since, as you see, it is not sealed.” 5° The

unsealed

enclosure was a

letter which Bernegger addressed on that same day, May

14, 1629, to

Bartsch about his chances of being appointed professor of mathematics at Strasbourg University:

By way of improving your chances, there is something else for me

to write about. But first I ask your permission, and I request you not

to misinterpret what I am suggesting out of the kindest and most affectionate feelings for you.

Last of all, let us agree to keep

about my advice, whether you approve it or reject it.

quiet

In your letter to me and also in the ephemeris [for 1629] which, to our great honor, you dedicated to us [the faculty of Strasbourg Uni-

versity], I noticed that you are a close friend of Kepler's. If you listen

to me, you will bind him even more closely to yourself by a family relationship. He has a marriageable daughter, whom I have never seen,

but she is well known to me through the letters which we have exchanged. For she has written to me quite often, so intelligently, so eloquently, that I could easily recognize her father's talents in the daugh-

ter too. . . . I realize what a risky throw of the mend a marriage. If it turns out badly, the entire those who encouraged it like marriage brokers. least afraid to urge you to court this girl. On the

dice it is blame is But I am contrary,

to recomthrown on not in the I am con-

fident that you, too, will surelv thank me most profusely hereafter. In the first place, as you

know

and as the world

is not unaware,

in

the kind of studies treated by her father he is a man whose peer has 57. Ibid., line 20.

58. Nova Kepleriana, 4, 95:16-17. «9.

Gesam.

Werke,

XVIII, No.

1108: 11-12.

Jacob Bartsch

187

not been seen in our time nor at any other time. Surely to have such a father-in-law is no mean distinction and no small satisfaction. Secondly, the girl herself has a character which is so pure, elevated, and sincere that these endowments all by themselves may seem able to inspire love for her. However, she is also supplied with another dowry,

which came to her from her mother’s legacy in no inconsiderable amount,

as I know

for a fact. This, of course, you, with

the self-

sufficiency of a philosopher, pay no attention to. But surely you should bear in mind that some day you will inherit those true treas-

ures of mathematics.

To

be sure, the great man

away from them even now, Still we may believe that he if you bind yourself to him ommend you very strongly

does not keep you

as they are the open doors of the Muses. will reveal them to you much more freely in this relationship. This in itself will recto us and, as I said in the beginning, im-

prove your chances for the appointment which we want. Consequently it will be one of the main arguments on your behalf and against your competitors, I have no doubt. What then stops you from alc father for his daughter? Or have you perhaps already asked

im?

As

we

saw

above,

Bernegger

addressed

the

foregoing

letter

to

Bartsch, and enclosed it unsealed in a letter of the same date to Kepler. Bernegger proceeded to explain to Kepler why he had left his letter to Bartsch unsealed: "If you think that any further advice should be given, I recommend that you have it added in an unfamiliar but professional handwriting. The sheet on which it is written should be enclosed in my letter [to Bartsch], as though my secretary had written it at my dictation. Seal my letter in this way, and send it in this way, so that he [Bartsch] won't be able to infer from our combined effort what we did. This matter is and will continue to be of great interest to me." ?! Bernegger's clever little scheme did not work, as Kepler informed

him on July 12, 1629: 2

This time you wrote in vain. . . . You

wrote

in such a way

that

anybody would readily detect someone else adopting your style. Your handwriting, stationery, and eulogy, elegantly combined, are elevated above your usual manner. Nevertheless, Kepler assured Bernegger, encouragement."

Bartsch

"does not need

your

During the past three months almost all the letters from that man have

been crammed with what he seemed from many indications to want.

But being inhibited by bashfulness or disinclination to do anything out of line, he preferred hints to an open request. He is a man of philo60. Briefe G. M. Lingelsbeims, ed. Reifferscheid, pp. 859-60. 61. Gesam. Werke, XVIII, No. 1108:12-16.

62. Ibid., No. 1111:6-57.

188

Appendix A

sophical disposition, being satisfied to refrain from specific language

and reserving that formal mode of speech for ceremonial occasions only. At other times he expresses the entire range of his plans in cir-

cumlocutions, for which no Oedipus is needed. . . . Since he tells me that he is coming here as my guest, it behooves me to wait him out. It

would be foolish for me to urge him on at the present time. I have exactly the same reason to keep quiet now until I am asked directlv, as I previously had to ascertain the thoughts in his mind. The reason is that my daughter is so far away. I was afraid that, deluded by a misconception, I might neglect my daughter's advantage by disregarding other possibilities there. Here I must now be careful not to make any promises to the good man (or send him your letter, which would take the place of a promise) which perhaps it will not be in my power to fulfill, if in the meantime

arrangements

are made

for my

daughter

by

my relatives, and the situation is no longer undecided. That 1s how things stand now in the affair. He thinks that it is improper to ask me for her hand when he has not seen her and she has not seen him. And yet he can not bear to wait until he can get to see her. He is heading for the Frankfurt fair. But from your letter to him I learn manv things, etc.

These "many things" were evidently not to Bartsch’s credit, since Kepler goes on to say: "Yet none of these things frightens me." Kepler's original letter has been lost, and is known only from a printed

book, entitled Letters Excbanged by J. Kepler and M. Bernegger (Strasbourg, 1672).9? The editor of this book was Matthias Bernegger's son, Johann Kaspar Bernegger (1612-75). He did not regard it as his duty to print his father's correspondence with Kepler exactly as he found it in the handwritten letters. On the contrary, he suppressed some letters altogether. In others, he felt free to introduce alterations. In still others, like ours, he made deletions.9?: In his letter of July 12, 1629, to Matthias Bernegger, Kepler continues: From your letter to him [Bartsch] I learn many things, etc. Yet none of these things frightens me, so long as I believe him to be an energetic and hard-working man, who can perhaps make a living just as

easily as a richer but careless man can lose his fortune in these harsh times. Hence, if you have anything positive to tell him about a professorship at Strasbourg, write him another letter. There is no need of arguments to urge this thing on him for which he himself has been striving for some time. Accordingly, see whether this proposed relationship

between

us will

really

increase

the

hope

of a professorship.

63. Epistolae J. Keppleri et M. Berneggeri mutuae (Strasbourg, 135-47. 64. Briefe G. M. Lingelsheims, ed. Reifferscheid, p. 958.

And

so,

1672),

pp.

Jacob Bartsch

189

finally, I do not forbid you to write. Since you detect his plans regarding this relationship, it seems by no means out of place, etc. Again “etc.” indicates that the suggestions which Kepler went on to make offended the editorial sensibilities of J. K. Bernegger. After this second

deletion,

Kepler

continues:

But there is more to tell you so that you may understand the full ex-

tent of our plans. That unhappy man came to me recently in order to inform me about his ideas for shaping his life in the way I mentioned before. He conceived the hope of living nearby, I suppose, for the purpose of paving the way to proposing soon thereafter. When

Kepler

displayed

an offer which

he had

University of Rostock, Bartsch did

not

expect

that.

For

if he

had

known

about

received it in

from

advance,

the he

would have said, I believe, that he had decided to leave his native land, which is in danger, and to seek a place for his studies on the coast. As it was, when he heard about Rostock, he left me without saying a

word about my daughter. Yet in a subsequent letter he showed that he was persisting in his intention. I am awaiting a new maneuver. I write and I also do everything most generously that is related to helping him. But I stick to generalities. I cover up his peculiar circumlocutions,

or else

I let them

pass

in silence.

For

in Austria

it is the

custom that the father is asked in explicit language by the proper men

to whom, as his sponsors, the suitor is held obligated, so that he cannot withdraw from his suit before he has received a reply.

With regard to his daughter Susanna, Kepler told Bernegger: I see nothing better for me to do than to turn over to you the functions of the father. Write to my daughter, or rather your daughter, asking her to let you know whether she is really free; whether she wants to get married, if her father's consent is not withheld; and whether she thinks she can safely trust you and your eyes, if you pick a husband for her whom you can't produce in person because he is so

far away, my functions as father having been transferred to you. To

you, then, as the one who is aware of what is necessary, I shall refer

the suitor, if he makes any clear request before he has seen her. You will talk to him; you will choose the place for the wedding; you will be present in my place.9?

On July 29, 1629, Bartsch notified Müller that "recently Kepler has been living with me here" at Luban.®* And then, finally, on September

1, 1629, Bartsch proposed and Kepler accepted.9* After a crafty rival 65. Gesam.

Werke,

XVIII, No.

1111:82-91. Kepler knew

customs at first hand, as both of his marriages 66. Ibid., No. 1113:9. 67. Ibid., No. 1114.

the Austrian

had been contracted

marriage

in Austria.

190

Appendix A

suitor was eliminated, “a student from Luban, returning Strasbourg, reported that Bartsch had reached Strasbourg

ber 7/17, and that on November

13/23

home from on Novem-

. . . he left that city on his

way to Durlach," where Susanna Kepler was then working.9? “Having received from her father a letter carried by his private courier, the Margrave [of Baden-Durlach] released her to me as my betrothed, and she is now living in Bernegger's house” in Strasbourg, Bartsch in-

formed Müller on January 9/19, 1630.5? On the previous day Berneg-

ger had already written to Kepler that Susanna was in his home.”

Then Bernegger gave Kepler a glowing description of the wedding on March 2, 163o. Among those present were Bartsch's brother Fred-

erick, and Kepler's son Ludwig.7! “When Bartsch went to Frankfurt with his wife, my on April 22, 1630, “and from there wrote to Bartsch dated the dedication of the second

the wedding was over, daughter,” Kepler stated his family in Luban.” ” edition of Kepler’s Ad-

monition “at Frankfurt during the spring book fair in the year 1630,

when the sun in conjunction with Mercury was in opposition to the moon, according to the new Tychonico-Keplerian computation" (about April 12, 1630).? On May 6, 1630, with a feeling of relief, Kepler remarked: "I finally received my son-in-law and my daughter."74

Bartsch had been advised by Bernegger, it will be recalled, that mar-

riage to Susanna Kepler would improve his chances for an appointment to the faculty of Strasbourg University. And in fact, about a week before the wedding, Bartsch was named professor of mathematics, on

February 22, 1630.75 Although he received the appointment, he never

actually taught mathematics at Strasbourg. The professor whose substitute or successor he was expected to become, refused to step down, and long outlived him.’® On June 21, 1631, Matthias Bernegger told

Schickard that he had received “for distribution among his colleagues" copies of poems celebrating Bartsch's wedding. However,

I didn't

distribute

them,

for

other

reasons

as

well,

but

mainly because I realized that the title "Professor Designate" in print, although correct, would nevertheless be viewed with jaundiced eves 68. Ibid., No. 1120:28-31. 69. Nova Kepleriana, 4, 97:last line-98: t.

70. Gesam.

Werke, XVIII, No. 1121:1-3.

71. Ibid., 422:20-22. 72. Ibid., 429:28-29.

73. Frisch, VII, 590:32-34; 654, April:3-6. 74. Gesam. Werke, XVII, No. 1135:2-3. 75. Berger-Levrault, Annales, p. 9, Gesam, Werke, XVIII, 422: 18-20.

76. Berger-Levrault, Annales, p. 156,

Jacob Bartsch

Ig!

by his predecessor, who is still alive and well, and by a few others who were not much in favor of his appointment. Bartsch had decided to come here with his family this past Easter. I urged him not to do so without the prior knowledge and consent of the university authorities. I also told him that there was scarcely any hope of getting an unusual salary when even the ordinary salaries are paid with difficulty in these hard times.?? As professor designate of mathematics, Bartsch received no salary,

taught no students, and did not reside in Strasbourg. Instead he assisted his father-in-law at Zagan. For example, Kepler had computed a table

of logarithms from o' to 60’ at intervals of 5"; these 720 logarithms he called his “Heptacosias” as a convenient round number (700).78 To spare the computer the labor of finding the proportional part, Bartsch reduced

the interval to one second,

Bartsch

his

tacosias” five times. The

resulting

“Trichil-Hexacosias.”

thereby

enlarging

3600 logarithms

Not

long

after

he

Kepler’s “Hep-

were

began

named to

by

print

these tables, Kepler died. Because of the ensuing confusion, the tables

were marred by numerous typographical errors. These were corrected

in a second edition entitled the Handy Logarithmic Tables of Johannes Kepler, the Imperial Mathematician, and Jacob Bartsch (Strasbourg, 1700). According to the editor, Johann Caspar Eisenschmidt (1656-

1712), Bartsch died of the plague.*? Unfortunately Eisenschmidt failed

to indicate how he learned that Bartsch exactly when that sad event occurred.

had

died of the plague,

and

There are conflicting statements about the date of his death, just as

there is disagreement about the year in which he was born. According to the records of Strasbourg University, Bartsch was born in 1600.9? Tipping the balance in favor of this date is the Strasbourg regulation governing candidates for the M.D. degree. Since the medical faculty wished to admit nobody younger than twenty, every applicant was required to state his age (“seine Testimonia et Documenta vitae ante actae mit sich bringe," to quote the characteristic mixture of German

and Latin).8! On the other hand, the author of a dictionary of intellectuals from Upper Lusatia dated Bartsch’s birth in 1599.7? But since this local historian cited no source for his statement, the Strasbourg date of 1600 for Bartsch's birth seems more reliable.

The same cannot be said about Berger-Levrault's date for Bartsch's

77. Epistolae W. Schickarti, pp. 161-62.

78. Frisch, VII, 412:14-16. 79. Tabulae manuales logarithmicae, ed. 1700, p. 8; Frisch, VII, 302:9-10.

8o. Berger-Levrault, Azmales, p. 9.

81. Ibid., p. xli. 82. Otto, Lexikon, I, 41.

192

death,

Appendix

December

26,

1633.9

A

Presumably

Bartsch

himself

told

the

Strasbourg authorities that he was born in 1600. But who told them when he died? On May 5, 1631, Bartsch informed Müller that the military situation had compelled him not long before to leave Zagan and join his brother in Luban.® It was there that Bartsch died. How well informed were people in Strasbourg about events in Luban, nearly four hundred miles away? Take the case of Bernegger, who had a special reason to be well informed. He wrote to a friend: “Jacob Bartsch, of blessed memory, the doctor and mathematician,

Kepler’s son-in-law,

owes

me

85 Reichsthalers.

More

than

once

his

widow promised to repay. Now that she is dead, I don’t know whom I should ask for the money.” ® The correctness of Reifferscheid's date

for this letter, January 12, 1636, was confirmed for me by the director

of the manuscript division of the State and University Library of Hamburg, where the letter is still preserved. In other words, Bernegger

believed at the beginning of 1636 that Susanna Bartsch was dead. Yet

more than two years later, on February 6, 1638, Ludwig Kepler ferred to his sister Susanna, Bartsch’s widow, as very much alive "married to a second husband.” 8° Since Bernegger in Strasbourg convinced that Susanna Bartsch was dead while she was still living, we not justified in being skeptical about Berger-Levrault’s date of

reand was are De-

cember 26, 1633, for Jacob Bartsch’s death? Is it anything more than a repetition of the same unsupported date given in Weidler’s History of Astronomy? 8" There is, on the other hand, some evidence pointing to an earlier date. For instance, the library of Tubingen University still possesses a copy of one of Kepler’s works in which Schickard wrote a marginal 83. Berger-Levrault, Annales, p. 9. 84. Nova Kepleriana, 4, 101:10-11, 23-24. 85. Briefe G. M. Lingelsheims, ed. Reifferscheid, p. 861. 86. Galileo, Opere, XVII, 279:61-62. 87. Johann Friedrich Weidler, Historia astronomiae (Wittenberg, 1741), p. 455. Weidler's date of December 26 may have been derived, directly or indirectly, from Henning Witte's Diarium biographicum (Danzig, 1688). Witte placed each of his brief biographies under the year in which the subject died. Within each

year Witte's notices were arranged by month and day. But what about the many instances in which Witte knew

(or thought he knew)

the year, but not the month

and day? Such examples of incomplete chronological information were regularly grouped by Witte within the given year, after the last precisely dated entry of

that year. Thus, in our case, under 1653, Witte's latest entry by month and day is December 26 (fol. Ggir). This is followed by fourteen notices concerning persons (including Bartsch) who died in 1633, according to Witte’s sources, which pro-

vided him with the year, but not the month and day, in those fourteen instances.

Jacob Bartsch note to the effect that Bartsch

193

died in 1632.88 In Susanna

prayerbook, now in the Archives of the Academy

Bartsch’s

of Science in Lenin-

grad, “an old family chronicle reports that Bartsch died of the plague

in Luban in the house of Sigismund Vogel in 1632.” 5? Sigismund Vogel, the author of this chronicle, married Susanna’s granddaughter

in 1690; his statement about Bartsch’s death agrees with the notation on the back of Bartsch's portrait.? Bartsch’s death was dated in the year 1632,

Johann

also

without

Daniel

month

Schulze,

or

day,

specified

by

Otto;?!

December

but

25.92

his

Both

continuator,

Otto

and

Schulze, however, failed to supply any source for their dates. In like manner, without indicating his source, Frisch dated Bartsch's death on August 15, 1632, and he was followed by both Adolf Schmetzer ?*

and Caspar. Yet in a correction sheet Frisch altered the date of Bartsch’s death to August 15, 1633.°° Without any warrant the year was pushed further along to 1634 by Otto J. Bryk.?? Thus we find Bartsch's death dated in 1632 (Schickard, Vogel, Otto), on August 15 (Frisch, Schmetzer, Caspar) and December 25 (Schulze), as well as in 1633 (Witte), on August 15 (Frisch) and December 26 (Weidler, Berger-Levrault), and in 1634 (Bryk). Whichever

of

these

conflicting

dates

turns

out

to

be

right,

one

thing

is

indisputably clear: the plague robbed mankind of a highly promising man at a regrettably early age. 88. 89. go. gt. 92. 93. 94. 95. 96. 97. 1918),

Martha List, in Geschichte und Entwicklung der Geodäsie, 1961, 2:32, n. 35. Ibid., p. 7. Stöckl (ed), Kepler-Festschrift, pp. 198-99. Lexikon, I, 41. Supplementband, p. 14. Frisch, VIII, 25: 1. Stöckl (ed.), Kepler-Festschrift, p. 88. Bibliograpbia Kepleriana, p. 106. Frisch, VIII, p. cxvi; cf. p. 945: 1. Johann Kepler, Die Zusammenklange der Welten, ed. and tr. Bryk (Jena, p. xliii.

Appendix B LUDWIG

KEPLER

Ludwig Kepler, son of Johannes Kepler and his first wife, Barbara Müller, was born in Prague on December 21, 1607.’ In signing the Dedication of his father’s Dream, Ludwig put the letters “M.A.” after

his name, since he had received a Master

of Arts degree from Tübin-

gen University on February 11, 1629. He had previously been awarded a Bachelor of Arts degree on March 14, 1627. In signing the Dedication of the Dream, Ludwig called himself also a “Candidate for the Doctorate in Medicine.” A "candidate in medicine" was a student who declared himself ready to be examined, deposited his fees, and was found to be qualified for the final examination. If he passed it, he was required to write a dissertation, submit it for approval, have it printed, and defend it publicly. Until the defense was successfully completed, the student was only a candidate. Medicine, however had not been Ludwig Kepler’s first love. His earlier interests included poetry, philosophy, and sculpture. But in October, 1628, while he was a student at Tübingen University, he entered the medical course. Four months later, on February 11, 1629, as we saw above, he received his master’s degree.

Ludwig began the study of medicine, then, before he received his

master’s

degree.

But

he

withdrew

from

Tübingen

in

the

spring

of

1629. His reason for quitting was made quite clear in the very strong letter of recommendation which he received on April 8, 1629, from the

dean and medical faculty. They said that they would have been happy to have Ludwig remain with them “if an opportunity to continue his studies at lesser expense elsewhere had not been offered to him." ? This opportunity came to him when, “with the support of the university he was appointed the traveling companion of the highborn and most noble Johann Dieterich of Karpfen [now Korpona in Hungary], only son

of the retired chief justice of Wiirttemberg, with whom

he was to be

1. Caspar, Kepler, tr. and ed. Hellman, p. 174; Frisch, VIII, 775:3-2 up.

2. Matrikeln . . . Tubingen, Il, 167.

3. Frisch, VIII, 906:17 up.

194

Ludwig Kepler sent to France in 1630. But Ludwig

195

preferred to remain in Basel.” 4

Without the young man whom he had been engaged to escort, Ludwig matriculated as a student of medicine at the University of Basel on

August

19, 1630.9 “At the time of his entry” into the second medical

school he attended, “he conducted a disputation presided over by the outstanding physician Stupanus. For a whole year Ludwig devoted his

energies to the art of medicine." ® In the course of that year on May 10, 1631, Ludwig inscribed his name in a friend's album, which is still preserved at the Historical Museum in Basel.” But the collapse of his arrangements

with the young

nobleman

had

left Ludwig

in financial

straits. Shortly after young Kepler had arrived in Basel, Bernegger wrote to Johannes Kepler on September 8, 1630: “If your son Ludwig,

who is now in Dasel, seeks to borrow some money, as he seems to be about to do, should I lend it to him? I am prepared to do so, unless you absolutely forbid it."5 Then, on April 25, 1631, Bernegger told Schickard that in a letter sent from Basel Ludwig said he was "involved

in debt difficulties, in which he has already asked me for help several

times." 9 Three months later Bernegger reported to Schickard: “The people at Basel were angered by Ludwig's unexpected departure. I have satis-

factorily placated them by promising in a letter to the Rector Magnifi-

cus that, unless Ludwig pays back all the money he owes to the people at Basel, I won't let him leave town. To prevent this promise from perhaps injuring me, please put pressure on his relatives, if you have any influence along those lines.” !? 4. Hansch,

Epistolae,

p. xxxiii. Had

not Hansch

(pp. i, xxxii-xxxiv)

reprinted

excerpts from an obituary of Ludwig Kepler, which was published by the rector and academic senate of Konigsberg University on the occasion of Ludwig's funeral,

pletely.

that

invaluable

document

would

5. Matrikel . . . Basel, Ill, 326. 6. Hansch, Epistolae, p. xxxiii. Emanuel

in

all likelihood

Stupanus

have

(1587-1664)

vanished

com-

was the professor

of theoretical medicine at the University of Basel; see Athenae Rauricae

(Basel,

1778), pp. 217-18; Albrecht Burckhardt, Geschichte der medizinischen Fakultät zu Basel 1460-1500 (Basel, 1917), pp. 169, 440. Stupanus was later cited by Ludwig in

his treatise on the Königsberg epidemic in 1649

anni 7. 8. 9.

1649, Elbing, 1650), p. 9. Matrikel . . . Basel, III, 326. Gesam. Werke, XVIII, 439:32-35. Epistolae W. Schick-rti, pp. 157-58.

(Febris epidemia Regiomontana

10. Ibid., pp. 167-68. Bernegger's promise to hold Ludwig in Strasbourg until his debts in Basel were paid off was not kept when, less than three months later, Ludwig left Strasbourg bearing a letter from Bernegger to Bartsch. Bernegger could not keep his promise then, since Ludwig had been summoned to the division

196

Appendix B

In this letter of July 26,

1631, Bernegger

said that Ludwig

“is now

living with us” at Strasbourg. Young Kepler had in fact enrolled as a student of medicine at the university on July 18, 1631.’ Here, in the third medical

school

he attended,

he was

disputation in the month of October, 1631. Galen,

the

greatest

physician

of the

the respondent ancient

Roman

in a formal Empire,

had

composed a treatise in Greek on The Causes of Symptoms. The second of the three

books into which

this treatise is divided was summarized

by Ludwig (or by his mentor) as a series of 121 theses. This summary was printed at Strasbourg in 1631 as part of a work published by Ludwig's

mentor,

Melchior

Sebisch,

Jr., who,

it may

be

recalled,

eight

years before had presided also over some of Jacob Bartsch’s medical

disputations.!?

“In the meantime [Ludwig] was informed about the death of his distinguished father, who had died at Regensburg. Ludwig was entreated

to return to his family and attend to the inheritance.” !? When he left Strasbourg for Regensburg, he carried with him a letter from Bernegger to Bartsch dated October 16, 1631.14 At Regensburg Johannes Kepler's estate was divided up among his survivors according to an

agreement which they made on November

3o, 1631. This agreement

itself has not survived, but it was listed among the documents

ing to Johannes Kepler's widow at the time of her death.’ After Ludwig

the division of his deceased father’s went to Linz. There his claim for

belong-

legacy at Regensburg, the money which the

Estates of Upper Austria owed to Johannes Kepler was registered on February 4, 1632.1° Two months later, having received a written ac-

knowledgement of the debt, but no cash, Ludwig left Linz.!* From the capital of Upper Austria he proceeded to Vienna, the capital of the Holy Roman Empire. There he collected the unpaid part of his faof his deceased father's estate, with his share of which creditors. 11. Matrikeln . . . Strassburg, II, 12.

he expected

to satisfy his

12. See Appendix A, p. 179, above. Sebisch is cited twice in Ludwig's Febris epidemia, pp. 42, 78.

13. Hansch, Epistolae, p. xxxiii. 14. Martha List, in Geschichte und Entwicklung der Geodäsie, 1961, 2:7, 32, n. 29; the letter is preserved and unpublished. 15. Stockl (ed.), Kepler-Festschrift, p. 113. 16. Frisch, VIII, 931:6 up-932:5; see also Dream, fn. 2, above. 17. Frisch, VIII, 932:22-16 up. Was it at this time that Ludwig had the difficulties with the provincial physician of Upper Austria which he recalls in the epilogue of his Method of Harmonizing tbe Discordant Sects in Medicine ( Metbodi conciliandarum sectarum in medicina discrepantium sectio prima, Königsberg, 1648)?

Ludwig Kepler

197

ther’s salary on June 8, 1632.18 Nearly a year later, on April 27, 1633, the huge sum still owed by the emperor to Johannes Kepler’s estate was officially acknowledged. These largely unsuccessful encounters with officialdom over money matters are discreetly omitted from Ludwig's obituary. It passes with-

out

an interlude

from

the

settlement

of

Johannes

Kepler's

estate

(which occurred, we may remember, on November 30, 1631) to Ludwig's association with Baron Sinzendorf. The obituary says, referring to the settlement: “When this matter was accomplished as desired,

Ludwig went to Geneva, in 1632, with Johann Joachim von Sinzen-

dorf, son dorf." 20

of the

highborn

and

This date, in all probability,

illustrious

should

lord

August

be “1633.”

Did

von

Sinzen-

the obituary

fudge the chronology in order to make the time gap between Regensburg and Geneva less obvious? When Ludwig set out for Regensburg,

let us recall, he was to deliver Bernegger's letter of October 16, 1631. On October 15, 1632, Bernegger declared: "Since I accepted the obh-

gation of a surety for him [Ludwig] both here [in Strasbourg] and with the people at Basel, I was very much concerned to know where he was. For more than a year I have heard nothing from him." ?! If Ludwig received the imperial treasury's promissory note of April 27, 1633, in person, then he and his companion, Baron Sinzendorf, must

have

left Vienna

shortly thereafter. For on May

13,

1633, Ludwig

Kepler and Baron Sinzendorf, hereditary cupbearer of Upper Austria, were registered at the University of Geneva.? They both entered their names in the official album reserved for foreign students of noble

birth,

Ludwig

Kepler

Geneva, “having house assiduously count of certain furt,” according

dating

his entry

on

December

14,

1633.

In

been accepted by the physicians, he visited the poorand continued this practice for a whole year. On acbusiness matters he was compelled to go to Frankto the obituary,?? which did not specify the nature of

these business matters. On August 9, 1634, Ludwig was in Regensburg, where he presented to the city a copy of his father’s Rudolphine

Tables in which he drew the family’s coat of arms.?* It would appear, then, that Ludwig's year of medical practice among the poor people of 18. Frisch, VIII, 928:11-9 up. r9. Martha List, in Geschichte und Entwicklung der Geodasie, 1961, 2:8, citing unpublished documents. 20. Hansch, Epistolae, p. xxxiii; for Baron Sinzendorf, see Dream, fn. 3. 21. Epistolae W. Schickarti, p. 179. 22. Stelling-Michaud (ed.), L’Académie de Geneve 1559-1878, p. 178.

23. Hansch, Epistolae, p. xxxiii. 24. Stóckl

(ed.), Kepler-Festschrift, pp. 89, 95, opposite 104.

198

Appendix B

Geneva extended from the spring or summer of 1633 to the spring or summer of 1634. Whatever the nature of the business that compelled

him to go from Geneva to Frankfurt, it did not prevent him from traveling farther east to Regensburg, perhaps in connection with his

deceased father’s funeral expenses. On February 15, 1634, Bernegger referred to a sum of money which

was owed to Johannes Kepler’s estate: “The student, Bartsch’s relative, to whom this money belongs, yearns for it with intense longing." ^? A month later, on March 14, 1634, Bernegger wrote: “The Kepler

money has me greatly worried. Even more anxious is that good stu-

dent, who has had to do without it for so long. We have tried various devices. Nothing works.” 2° Was there perhaps a Frankfurt publisher

who was ignoring demands from a distance that he pay what he owed to Johannes Kepler’s estate? Were

these the business matters that com-

pelled Ludwig Kepler to go in person to Frankfurt? If he succeeded in obtaining the money

due him as his father’s heir, is that how

he man-

aged to finance the printing of the Dream’s title page and dedication at

Frankfurt? If so, his success was not known in July, 1634, to Bernegger, who was then engaged in translating Galileo’s Dialogue of 1632 from Italian into Latin.?” The great Tuscan scientist, the fourhundredth anniversary of whose birth in 1564 has recently been celebrated all over the world, had been sentenced to prison by the Roman Catholic church, and his Dialogue prohibited. But this prohibition carried no weight in countries which had been freed from the shackles of the Holy Inquisition. Together with his translation of Galileo, Berneg-

ger planned to publish another pro-Copernican work that had been prohibited and condemned. “T shall add also Johannes Kepler's Lunar Astronomy, from which unanswerable arguments in favor of Copernicus can be drawn. So far as I know, that book has not been published ” Bernegger stated on July

10, 1634

(old style), in a letter subse-

duently published in his Correspondence with Famous Scholars, second fascicle.?8

Some two months later Ludwig Kepler published the Dream or . Lunar Astronomy at Frankfurt. "Here he became friendly with

25. Epistolae W. Schickarti, p. 190. 26. Ibid., p. 195.

27. Enelish translation by Stillman Drake (Berkeley and Los Angeles: University of California Press, 1962). Bernegger's translation. (Dialogus de systemate mundi, Strasbourg, 1635) included as an appendix (pp. 459-64) Kepler’s defense of the compatibility of Copernicanism with the Bible (see Kepler's Notes on the Dream, fn. 32). 28. Bernegger, Epistolaris commercii secundus ( Strasbourg, 1670), p. 76.

cum

viris

eruditione

claris

fasciculus

Ludwig Kepler His Excellency

ambassador

Robert

to Germany.

Anstruther,

199

the king

This gentleman

of England’s

recommended

him

special

in the

highest terms to the Scottish nobleman George Douglas, who had been sent to Prussia for the negotiations between Poland and Sweden. With George Douglas, Ludwig Kepler came to us,” say the Kónigsberg authors of Ludwig's obituary.??

Ludwig journeyed from Frankfurt to Danzig as a member of Doug-

las’ retinue. According to the latter’s secretary, when Douglas received his credentials as “Lord Ambassador Extraordinary from the king of Great Britain to the kings and crowns of Poland and Suethland . . . in this new condition, his first work was to furnish himself with necessaries and attendants suitable to that high employment.” ?? When the mission returned to England, its papers were turned over to the principal secretary of state?! and they are now in the Public Record Office.? A preliminary search by Mrs. Nancy Sabra of Alexandria,

United Arab Republic, has failed to disclose in what capacity Ludwig

served Douglas.

"After a long and tedious winter

which

they left in December,

journey

1634, Douglas

from and

Frankfurt/Main," his party arrived in

Danzig on January 9, 1635.7? A few months later, during the Easter season, Peter Crüger (1580-1639), the city mathematician of Danzig,

who had been a good friend of Ludwig’s father, wrote: “. . . during

the past winter Ludwig Kepler came here with the king of England's ambassador. . . . Ludwig stayed at my house a couple of times, but afterwards he left for the Duchy of Prussia. He told me about the con-

dition of his stepmother with the remaining children. Amid very great danger, they had gone to Frankfurt/Main. He had left them there in the month of December (about the time the English ambassador had passed through there). They didn't have much money. He had to turn

over to his stepmother whatever he had saved up. Now he himself was destitute.” 3* Whatever the nature of Ludwig's connection with Douglas, it does not seem to have been very lucrative. He departed for Prussia long before the Swedish-Polish negotiations were completed. "While I was a traveler at that time, I was hospitably received at Pachollen by that 29. 30. don, 31. 32. 33. 34.

Hansch, Epistolae, p. xxxiii. John Fowler, The History of tbe Troubles 1656), p. 226, somewhat modernized. Ibid., p. 242. Foreign Papers, Poland, Vol. o, 1635-36. Fowler, History, pp. 142, 228-29. Nova Kepleriana, 4:111:3 up-112:4.

of Suethland and Poland

(Lon-

200

Appendix B

very noble and exceptionally learned man, Frederick von Pollentz, Jr.,

of blessed memory, thirteen years ago," Ludwig recalled in 1648.?? Pressing on to Konigsberg, he matriculated at the university, after having previously studied medicine, as we saw above, at Tubingen, Basel, Strasbourg, and Geneva in that order.

At

Königsberg

Ludwig

registered

on

May

11,

1635.°°

“He

was

sponsored by the late public professor, the excellent and distinguished

Dr. Loth." 3” This was the elder Georg Loth (1579-1635), who died on November 15, about half a year after he had sponsored Ludwig. Loth had been named personal physician of the Elector of Brandenburg-Prussia and court physician in 1613; in that same year he was appointed assistant professor of medicine; the following year he was

promoted to the associate professorship, and to the full professorship i In 1622; he was elected rector five times.** "Ludwig was accepted as a practitioner after an examination and a disputation about consumption." ?? This disputation (De pbhthisi,

Königsberg, 1636) was presided over by Daniel Beckher, Sr. (15941655). Beckher had been appointed assistant professor of medicine in 1623, city physician in one of Konigsberg’s subdivisions in 1625, associate professor in 1635 and at the same time court physician of the Polish king at an annual salary, full professor in 1636, and Brandenburg court physician in 1639; he too was elected rector five times.*? In his first rectorship, the winter semester of 1635-36, he described himself as “chief

physician

of

their

Sacred

Royal

Majesties

in

Sweden, etc. and physician in ordinary to the Kneiphof

Poland

and

borough of

Königsberg.” 4! The Konigsberg obituary continues: “After some time Ludwig left for Italy and acquired his doctoral degree at Padua.” ** This quiet narrative makes it appear that Ludwig's motive in leaving Kónigsberg was to obtain the highly regarded Paduan doctorate. Actually, as he later 35. Ludwig Kepler, Method, epilogue. Pachollen is a small village near Saalfeld in East Prussia. 36. Matrikel . . . Königsberg, I, 360. 37. Hansch, Epistolae, p. xxxiii. 38. Arnoldt, Historie der Königsbergischen Universität, pp. 104-5, 285, 301, 310, 324-25. 39. Hansch, Epistolae, p. xxxiii. Ludwig was admitted to practice some two

years before he acquired his medical degree, as he recalls in his Febris epidemia, p.

81.

40. Arnoldt,

314, 464.

Historie

der Königsbergischen

Universität,

pp.

105-7,

301-3,

310,

41. Matrikel .. . Königsberg, I, 363. In 1636 Ludwig lived in Kneiphof, as he

recalls in his Febris epidemia, P- 81. 42. Hansch, Epistolae, p. xxxiii.

Ludwig Kepler

201

explained in a communication to Galileo: “By means of a letter I was summoned by my sister" Susanna, Jacob Bartsch’s widow.*? Susanna, in Luban, urgently needed Ludwig’s help in protecting their father’s unpublished manuscripts from grasping officials. Ludwig’s letter to Galileo continues: “I tried to get through” from Königsberg to Luban, “and was stripped naked by the imperial troops. I arrived at my sister’s home, and found her, also, crushed by the most abject poverty. I procured clothing to safeguard my body from being injured by the winter, and also the traveling expenses for the trip to Vienna which I was undertaking, by practicing medicine for a few months. I started out

for Vienna nine months ago” (May, 1637, since Ludwig’s Galileo was dated February 6, 1638.) * Ludwig

letter to

went to Vienna in the hope of inducing the imperial treas-

ury to pay him some of the money, mentioned above, still owing to him as his father’s heir. His presence in Vienna on October 10, 1637,

was reported to Galileo by Giovanni Pieroni, the Imperial Architect.*? Ludwig’s trip to Vienna, however, accomplished nothing. “For three whole months,” he told Galileo, “I could get no answer.” “My relatives on my mother’s side, who live in Styria, generously gave me some money to take my doctoral degree in medicine. For this reason I am now leaving for Padua” from Venice, where this letter was written on

February 6, 1638. Iwo

days later he was enrolled as a member of the

German students’ organization at Padua University, where the expenses of an academic ceremony were notoriously high. He had told Galileo: “I can’t hope to have my ceremony elsewhere unless I get my

doctor's degree." *9 This he received on March

18, 1638.47

After Ludwig obtained the Paduan degree, "he went back again to Konigsberg." *? But he evidently had no reason to return in a hurry, for

a reply (dated August 12, 1638) to one of his letters was addressed to him in Vienna.4® On August 23, 1638, he put his personal seal on a

legal document

in Regensburg.??

been buried in the late summer

His

stepmother

had

died

there and

of 1636.9! But the inventory of the

43. Galileo, Opere, XVII, 278:31-32.

44. Ibid., lines 32-36. 45. Ibid., 193:31-32. 46. Ibid., 278:39-40, 279:64-70. 47. Volumes 275 and 465 of Padua University's old records, as I was courteously informed by Dr. Lucia Rossetti. 48. Hansch, Epistolae, p. xxxii. 49. Martha List, in Geschichte und Entwicklung der Geodäsie, 1961, 2:21; this

reply is unpublished.

50. Stóckl (ed.), Kepler-Festschrift, p. 101. 51. For the date, see the photocopy of the official burial record in ibid., opposite p. 89.

202

Appendix B

possessions she had left behind was not formally registered

until Feb-

ruary 27, 1637.°2 Ludwig’s legal action in Regenburg on August 23, 1638, was related to the division of his stepmother’s estate. Toward the close of 1638, he published at Passau A Medical Discourse, in which he

referred to his having been “at Königsberg in Prussia three years ago." 93 When Ludwig “went back again to Königsberg,” he entered Prussia for the second time. Although he now held advanced degrees in both

medicine and philosophy, he reregistered at Kónigsberg University. By

so doing, he reclaimed his rights as a member of the academic community, and was thereby relieved of certain municipal and provincial obligations. Anybody who wished to regain this desirable status after being away from Königsberg University for more than one year was required to reregister with the rector. When Ludwig did so on November 11, 1639, his action was deemed an honor and he paid no fee.?? About two months later, on January 2, 1640, he married the daughter of the professor of Greek.?9 “With his wife he went to Hungary and took care of the sick for three years.” ** He “was living in Sopron ten years ago," he sald in

1650.5 His medical activity there was interrupted twice. His first departure is dated in 1640 by an extant poem which was printed in his honor when he was leaving Sopron.

Secondly,

and reclaimed his academic rights" on May

“he returned to Prussia

30, 1642, again paying no

fee.°® Finally, “Ludwig was recalled from Hungary to Königsberg.” °' His recall may have been connected with an outbreak of the plague

at Königsberg in 1644.*! This epidemic may have been responsible also for his appointment as royal and ducal court physician,

and his desig-

2. Ibid., pp. 89, 99, 108.

53. Ein mediciniscber Discurs, fol. C1 verso.

54. Marrikeln . . . Königsberg, I, p. Ixix. 55. Ibid., p. 407. The same source reveals that Ludwig Kepler's servant, Johannes Ziegler, who came from Jihlava (Iglau) in Moravia, matriculated at the university on March 3, 1640 (p. 408). Since Ziegler was still below the minimum age of sevcnteen, he was not permitted to take the oath of obedience (p. Ixii). But he was old enough to be hazed in the usual manner (pp. Ixxii-Ixxiv). He paid no fee; like many other poor students, he earned his way by working as a servant. 56. Hansch, Epistolae, pp. xxxiii-xxxiv. Ludwig's wife gave birth to twins in 1642, and fell ill, as he recalls in his Febris epidemia, p. 6. His father-in-law died before 1650 (ibid., p. 4). 57. Hansch, Epistolae, p. xxxiii.

58. Ludwig Kepler, Febris epidemia, p. 85. The Hungarian name “Sopron” fol-

lows burg. 59. 60. 61.

the medieval Latin designation of the town, which in German Matrikel . . . Königsberg, I, 431. Hansch, Epistolae, p. xxxiii. Ludwig Kepler, Febris epidemia, p. 1.

is called Óden-

Ludwig Kepler

203

nation as physician in ordinary of the ducal suburbs in Königsberg.°? He uses these titles in his German poem mourning the untimely death of a brother of a high court official.® At the time of his recall Ludwig tried to gain admission to the medical faculty of Kónigsberg University by conducting a disputation on

the subject of the evil spirit (De incubo, Königsberg, 1644).9* Perhaps because he failed to become a university professor, vate school.® The disagreements among physicians orders and prescribing remedies were constantly in was particularly fond of repeating the old adage

many

opinions as there were

doctors. Some

he founded a priin diagnosing disLudwig's mind. He that there were as

of his colleagues disap-

proved of his procedures, as Ludwig plainly admits. Some such attitude perhaps explains why his campaign to gain an appointment to the medical faculty of Kónigsberg University fell short of its goal. Moreover, when the plague struck again at Kónigsberg in the spring

of 1649, at first Ludwig was not consulted, “as though he were a spec-

tator watching from across the river." 99$ At length a despairing patient called him, and when that sick man recovered, others sought Ludwig's services. The local physicians as a body were instructed to consider the epidemic in all its aspects and submit a written report to the authorities. Ludwig's diagnosis was rejected by his colleagues. Nevertheless, when the rector and academic senate of Kónigsberg University decided that a cadaver should be opened for the purpose of finding the cause of the epidemic, the autopsy was entrusted to Ludwig. When some of his col-

leagues claimed that his later diagnosis contradicted his earlier analysis,

he undertook to show that there was in fact no contradiction. This self-

defense was published in 1650 as Ludwig's Febris epidemia.9* The results of Ludwig's activities in 1649 and of his published ac-

count of them in the following year may be seen through his eyes in a letter which he subsequently wrote to a famous Danish physician,

Thomas Bartholin (1616-80), who printed it in his Medical Letters.°*

62. Edward Rosen, in American Historical Review (1960-61), 66:151. 63. Ludwig Kepler, Trostschrift über ... Joban Albrechten von Rauschken, who died on March 4, 1646.

64. Hansch, Epistolae, p. xxxiv. The

respondent in Ludwig’s

disputation was

Jacob Moldenhauer of Torun, who had matriculated and paid a tuition fee of 2 marks, 5 groschen on January 7, 1641 ( Matrikel . . . Königsberg, I, 417). 65. In this connection he published his Method, cited in fn. 17, above. 66. Ludwig Kepler, Febris epidemia, p. 11. 67. On the last page of this work, an epigram in honor of Ludwig is dated October 4, 1650 (p. 88). 68. Thomas Bartholin, Epistolarum medicinalium a doctis vel ad doctos scriptarum centuria secunda, No. 92 (Copenhagen, 1663; reissued, The Hague, 1740), pp. 704-7.

204

Appendix B

Ludwig’s letter to Bartholin began by referring to “Frederick Hammerich, candidate in medicine, who was once an auditor in the private school which I had founded for the purpose of harmonizing the discordant sects in medicine.” Hammerich, who was born in Altenburg,

enrolled as a student of medicine in the University of Leiden on July 14, 1666, when

he was thirty-six years old, and established in practice

at Helsingor (Hamlet’s Elsinore) in Denmark.“ His Inaugural Medycal Disputation concerning Contagious Carbuncle was published at Leiden Danish

in 1666.7° He subsequently became a doctor in the royal navy, and sent unusual specimens to Thomas Bartholin, who

discussed them in his Medical and Philosophical Activities in Copenhagen.™ In our letter, which was written on October 2, 1657, Ludwig Kepler told Bartholin that he had sent Hammerich a copy of “my Concept of Plague [Idea pestis, Lübeck, 1657], which was published by me here at Lübeck to gain admission. . . . Hammerich recently wrote to me . informing me that when he brought it to you to be examined, it was approved and taken from him. But he will have another copy in its

place, for I shall send many copies not only of my Concept but also of my Method ™ as well as of my Febris epidemia." The full title of this

latter work read as follows: “Königsberg Epidemic Fever, which at first was fatal only to students frequenting the common mess hall, but soon became dangerous to outsiders and banefully contagious among residents of both sexes." “The publication of this tract," Ludwig told Bartholin, “was under-

taken by order of the Academic Senate itself. Yet it paved the way for

my departure [from Kónigsberg] because I exposed the mistake of the university professors who attended to this disease from the outset. oince they ignored the true cause, within a fortnight about forty young men of the highest talent died miserable deaths." This mortality rate may seem high to us. Actually it was so low in comparison with

other plague years that 1649 was not even mentioned in a detailed his-

tory of the plague in East Prussia.“ 69. Album

LXXV

studiosorum | academiae

(The Hague,

1875), col. 530.

Lugduno

70. Christian W. Bruun, Bibliotheca Danica

I, 842. 71. Thomas

Bartholin,

1673-80), I, 53-54.

Acta

medica

Batavae

MDLXXV-MDCCC-

(Copenhagen, 1877; reissued, 1961),

et philosophica

Hafniensia

(Copenhagen,

72° Ludwig’s Method, which was dedicated to Beckher, was labeled “Part I," and since no further parts appeared, "it seems to have won little approval from the profession” (Christian Wilhelm Kestner, Bibliotheca medica, Jena, 1746, p. 166). 73. Wilhelm Sahm, Geschichte der Pest in Ostpreussen

(Leipzig, 1905).

Ludwig Kepler

205

“When I was called to take care of this disease,” Ludwig's letter to Bartholin continued, "God's grace blessed my labor and advice so that

not only were most of those who

were still sick restored to health

within a few days, but the disease itself was banished from the univer-

sity grounds." The regimen chosen by Ludwig was succinctly summarized by the great Swiss doctor Albrecht von Haller (1708-77) in his Bibliography of Practical Medicine, as follows: “He rejected bloodletting, administered enemas, and then prescribed cordials as well as Mercury of Life [ Algarotti’s powder ].” 74

An intriguing feature of Ludwig’s discussion of the 1649 epidemic is its place and date of publication (Elbing, 1650), although he says that “the publication of this tract was undertaken by order of the Academic Senate itself.” “With the approval of the Medical faculty of Königsberg University” another treatment of the epidemic appeared at Königsberg in 1649. Its author was Daniel Beckher, who had witnessed Ludwig’s autopsy. Was Ludwig's discussion of the 1649 epidemic repudiated by the Kónigsberg professors when they saw its contents? Was Beckher their spokesman or defender? Whether

or not this was the fact, Ludwig's

summed with the bitter reflection:

letter to Bartholin

re-

It seemed intolerable to my colleagues, however, that the prize should

be snatched from them by an outsider who was not a professor. By flattering and misinforming the courtiers, therefore, and by secretly

defaming me before the citizens, they succeeded in diverting the good

will of the court and of many citizens from me. My salary at the court [of the Elector of Brandenburg-Prussia] has now been withheld from me for six years. What is most important and is harmful to the public welfare, which they disregarded on account of their private hatred, they blocked the publication of Hipparchus as a posthumous

work of my father by stopping the payment

Joachims

which

had

been

earmarked

by

the

of the five hundred

Most

Serene

Elector

twelve years before for the printing of the said work. From the be-

ginning

they were

at once

jealous of me

because

I was

appointed

court physician. By reason of my guileless honesty I was not equal to

the task of breaking up their crafty plots. Hence, to get away from their arrogance and rudeness, I went to Lübeck and said goodbye to the Brandenburg court. For in this disturbed state of affairs, no matter how the Most Serene Elector had signified by word of mouth his most gracious affection for me, all my hope of obtaining assistance disappeared.

While Ludwig was still at Königsberg, and before he left for Lübeck, he was visited by Peter Crüger’s former pupil, Johannes Hevelius (1611-87). That renowned astronomer came to examine the 74. Albrecht vor 1776-88), IT, 638.

Haller,

Bibliotheca

wedicinae

practicae

(Bern

and

Basel,

206 unpublished

Appendix manuscripts

in

Ludwig's

B possession."

After

Ludwig’s

death, his heirs sold all of Johannes Kepler’s manuscripts and letters to Hevelius, who announced the purchase in his Machina coelestis (Danzig, 1673, p. 35). Hevelius drew up the first catalogue of the Kepler manuscripts, and it was published in Volume

of London's Philosophical Transactions

IX of the Royal Society

(1674). From Hevelius’ heirs

the Kepler collection came into the possession of Hansch.*® Our knowledge of Ludwig's career is obviously far from complete. Thus a poem honoring his memory speaks of his return from Lübeck to Kónigsberg as having been his seventh arrival in Prussia. From the records of Kónigsberg University we learn that Ludwig reclaimed his

academic rights on October 4, 1662; on account of his relationship to

his father and father-in-law, again he paid no fee.*? What are the six previous occasions on which he entered Prussia? His first entry was

connected with the British ambassadorial mission in 1635. In 1639 he

returned with a medical degree from Padua. Three times he came back

from medical practice in Hungary

(1640,

1642, 1644). Lastly, he re-

turned in 1662 from his unsuccessful effort to establish himself in Lübeck. What was his seventh arrival in Prussia, known to his poetic friend, but not to us? In a letter written on November 2, 1660, in Copenhagen, Thomas Bartholin mentioned that "Ludwig Kepler .. . in person recently showed me a treatise . . . as he was passing through." *? When Ludwig visited Bartholin at Copenhagen in 1660, he was probably on his way back from Lübeck to Kónigsberg, where he died three years later,

on September 13, 1663.9? Bartholin's sympathetic judgment of Ludwig

may serve as a fitting comment on his whole life: “He is a very learned man, and worthy of a better fate."

75. Pierre Gassend, T'ychonis Brabei . . . vita (Paris, 1654), Preface, fol. azv; Bk. 6, p. 243; 2nd ed. (The Hague, 1655), fol. ,2v, p. 209; and Opera omnia (Lyons, 1658), VI, 519. 76. Martha List, in Geschichte und Entwicklung der Geodäsie (1961), 2:24. 77. Hansch, Epistolae, p. xxxiv. 78. Matrikel . . . Königsberg, Il, 29. 79. Bartholin, Epistolarum medicinalium, eds. 1667 and 1740, p. 36 (3d century, No. 8); and De insolitis partus humani viis dissertatio nova (New Dissertation on Unusual Ways of Human Births), Copenhagen, 1664, p. 95; ed. The Hague, 1740, P- 748o. Hansch, Epistolae, p. xxxiv.

Appendix C KEPLER'S

In

1593, while

LUNAR OF

DISSERTATION

1593

Kepler was a student at Tübingen

University,

he

wrote a dissertation about the moon. On the basis of this dissertation, his fellow-student and friend, Christopher Besold, formulated about twenty theses. Besold then showed these theses to Professor Veit Müller, who was in charge of the philosophical disputations. But Müller refused to approve a debate over the theses, as Kepler pretty plainly implies.! The reason why the disputation did not take place was explained by Kepler two years later in a letter to Mastlin, the only pro-Copernican member of the Tübingen faculty: “With regard to the others who are under the authority of the University, I am afraid that they will be

unwilling to contribute

[to my forthcoming Cosmographic Mystery |

anything opposed to the traditional opinion. This was demonstrated in particular by Professor Müller in the disputation concerning the moon which I wrote and which Besold would otherwise have been prepared to defend." ? Kepler wanted the three Hohenfelder brothers, who were not mem-

bers of the Tübingen faculty, "to express their opinions [in his proCopernican Cosmographic Mystery] in verse or in prose, whichever

they prefer, for they are free" ? to accept new ideas. With this intellectual freedom of the three brothers Kepler contrasted the bound condition of the faculty, who were "under the authority of the University." With sincere gratitude Kepler continued to address Mastlin, his professor of mathematics and astronomy, as his "highly revered teacher" even after being appointed Imperial Mathematician.* On the other hand, no such warm personal relationship developed between Kepler 1. 2. 3. 4.

See Kopler's Note 2 on the Dream. Gesam. Werke, XIII, 39:241-44. Ibid., lines 240-41. Ibid., XVIII, 25:717-18. 207

208

Appendix C

and Müller. In 1595 Kepler frankly admitted:

“I do not regard him as

one of my intimate friends.” > But two years later, when Müller was the dean at Tubingen, he was invited by Kepler to attend his wedding. A clue to Kepler’s conduct on that occasion may perhaps be provided by his confession: “I can’t incur the animosity of my teachers, on whose good will my safety depends.” ? Kepler’s prudent attitude while he still needed professors’ recom-

mendations may explain why the lunar dissertation of 1593, which he

wrote for himself, not for Besold, was nevertheless submitted to Müller, not by Kepler, but by Besold; and also why, deterred by Müller's adamant anti-Copernicanism, Kepler made no effort to defend his lunar

dissertation of 1593 in a public disputation at Tübingen.

5. Ibid., XIII, 20:35-36, 6. Ibid., 103:61, 119:236-38. In the latter letter, which is dated April 9, 1597, Kepler spoke of his wedding as an event still in the future. On February 9 he was engaged, on April 27 he was married (Frisch, VIII, 689:2 up). 7. Gesam. Werke, XIII, 20:25-26.

Appendix D KEPLER’S TRANSLATION PLUTARCH’S MOON

In his Optics of 1604 Kepler

presented

fourteen

OF

quotations

from

Plutarch’s Moon, not in the original Greek, but in a Latin translation.! Subsequently he became so intrigued by the fascinating discussions in the Moon that he decided to translate the entire dialogue himself, and to couple his Latin version of Plutarch with his own Dream. In a letter

addressed to the Imperial Librarian in Vienna on April 21, 1622, Kep-

ler referred to his Dream as follows: “I am working on a small book, which needs the help of Plutarch’s little work on The Face in the Moon. Xylander’s Latin translation of it is full of gaps, and what there

is, is full of obscurities. More light will be shed on it for me, I hope, by

the Greek text, however defective that may be. Therefore I earnestly beseech Your Excellency to send me a Greek manuscript copy... . But if a Greek manuscript is not available, send me at least a printed copy, for example of the Basel or some other edition.” ? What the response was to this request, we learn from a letter written by Kepler a year and a half later to Bernegger: “Iwo years ago, as soon as I re-

turned to Linz, I began? to recast my Lunar Astronomy, or rather to

clarify it by means of notes. But I clung to a vain hope for Plutarch's little book on The Face in the Moon in Greek, which is not being sent from Vienna by the man who promised it. By reading Xylander's translation I seem to detect what the philosopher meant to say in the gaps. Yet I am stuck. However, if the passages immediately preceding and following the gaps were accessible to me in Greek, I would make better progress.” * Two months later Bernegger replied: "I have H. Stephanus’ Greek

I. Gesam. Werke, Ul, 198:35-199:3; 199:3-7; 203:12-15; 207:21-24; 220:17-20; 238:16-17, 18-23, 29-31; 241:28-34; 250:36-251:3; 251:9-16; 254:34-37, 39-40; 259:23-26. 2. Ibid., XVIII, 87:6-88: 15. 3. Reading coepi instead of cepi.

4. Gesam. Werke, XVIII, 143:9-15.

209

210

Appendix D

edition of Plutarch, consisting of six volumes in octavo. If you wish, I shall send you the volume containing the essay on The Face in the Moon." * At the same time he suggested that the French king’s librar-

ian might be able to fill in the gaps from a manuscript in the royal

library. Kepler answered: "With regard to Plutarch, at present I should like to have a copy of at least the passages which immediately precede and follow the gaps in Xylander. In the meantime it will appear whether any help is forthcoming from the French library." ° No help was forthcoming from the French library, as far as is

known. According to a marginal note in the Somnium (1634 ed., p. 98), Kepler based his translation of the Moon from Greek into Latin

upon

a Wechel

imprint in 8?, containing

with the Moon at pages 1696-1742.

the Greek

text of Plutarch,

Wechel and his successors have been discussed by Hubert Elie,’ who listed only one Plutarch item. This was published by Wechel's heirs at Frankfurt in 1599. It is in folio, however, not in octavo, and it carries the Moon on pages bearing lower numbers than those cited in

Kepler’s Note 212 on the Dream and in the 1634 Sommniun?’s marginal

note. I have been able to locate neither a surviving copy of a Wechel Greek Plutarch in 8°, nor a bibliographical reference to it. On the other hand, there was an edition of the Greek text of Plutarch in 8?

with the Moon at pages 1696-1742. This edition was published, however, not by Wechel, but by H. Stephanus in 1572. It was the appropriate volume (Vol. 3) in this edition that Bernegger offered on Feb-

ruary 4/14, 1624, to lend to Kepler. It 1s altogether likely, therefore, that the Greek text of Plutarch used by Kepler was indeed lent to him by Bernegger; that it was published by Stephanus, not by Wechel; and

that the marginal note in the 1634 Somnium (p. 98) is wrong, the error being due presumably to Bartsch. For on May 5, 1631, Bartsch plainly implied ? that the whole of the Dream was completely printed, except

for the title page and dedication. On March 2, 1629, Kepler told Bernegger that to the Dream “I am adding Plutarch’s Face in the Moon. I have translated it anew, and have filled in most of the gaps from the context. This procedure was impossible for Xylander, who was not an astronomer by profession." ? In the Notes accompanying his translation of Plutarch, Kepler recalled: “I remember that when I was making the translation, I was dissatisfied 5. 6. 7. 8. 9.

Ibid., 155:11-13. Ibid., 176:54-57. Gutenberg Jahrbuch (1954), 29:181-97. See Introduction, pp. xxi-xxii, above. Gesam. Werke, XVIII, 386:48-51.

Kepler's Translation of Plutarch’s Moon

211

with Xylander, whose version reads as follows,” 10 whereas elsewhere Kepler accepted emendations that had been made by Xylander.!! Xylander was appointed professor of Greek at Heidelberg Univer-

sity in 1558, and five years later he switched to teaching Aristotelian logic. His surname had not always been Xylander. When

he was born

at Augsburg in 1532, he was christened Wilhelm Holtzman. But in his

student days with true humanist enthusiasm he replaced his vernacular family name, which meant “woodman,” by ıts Greek equivalent, Xylander. Among his many valuable contributions to classical philology a high place must be accorded to his Latin translations of Plutarch’s essays, including the Moon. Since Xylander’s rendering of

Plutarch’s Moon into Latin was originally published at Basel in 1570 and reprinted later, Kepler’s was not the first Latin translation. Kepler

made his translation of Plutarch apparently not long before

1629, if

that is the proper inference from his letter of March 2, 1629, as quoted above. In Note 21 on his translation of Plutarch, Kepler said that he

had refuted an error “26 years ago in my Optics” of 1604.12 Hence he wrote the Notes on his translation of Plutarch in 1630, the year in which he died on November 5/15. The fourteen excerpts from Plutarch’s Moon in the Optics of 1604 were quoted, with very slight modifications by Kepler, from Xylander’s translation.!? But these passages are quite different in Kepler’s own version, which was first published four years after his death." 10. 1634 Somnium, p. 127; Frisch, VIII, 108, n. 25:1-2. 11. 1634 Somnium, pp. 137, 139; Frisch, VIII, 111:14-13 up, and 112, n. 48. 12. 1634 Sommium, p. 124; Frisch, VIII, 107:9-10. 13. Ed. Basel, 1570, 768:1-4; 770:23-28; 772:51-55;

773:52-774:23

774:39-42;5

775 :28-30, 30-35, 43-44, 51-53; 776:56-57; 777:20-25, 27-29, 29-35; 778:6-9.

14. 1634 Somnium, pp. 102, 109-10, 117, 120, 129-30, 133, 135, 136, 138, 144, 145, 147. Reprinted in Frisch, VIII, 78:14-19; 81:3 up—82:3; 85:21-15 up; 87:4-11; 88:10-16; 89:22-24, 25-30, 13-12 up, last three lines; 91:16-14 up; 92:11-16, 19-21, 22-29; 93:13- 16.

Appendix E KEPLER

AND

DONNE

In his Note 8 on the Dream Kepler wrote: “I suppose that a copy of this little work fell into the hands of the author of the bold satire en-

titled Ignatius His Conclave, for he stings me by name at the very outset." Was Kepler’s supposition sound or unsound? On January 24, 1611, the Latin edition of John

Donne’s

Conclave

Ignati was entered in the Stationers’ Register.1 “Presumably it was written therefore late in 1610,” we are told.? On the other hand, in his Note 8 on the Dream Kepler tells us that “the first copy" of the manu-

script of his Dream “was taken from Prague," where he was then living, “to Leipzig and from there to Tübingen in the year 1611." Therefore no manuscript copy of Kepler's Dream could have been in the

hands of the author of Ignatius His Conclave

while that satire was

being written. Consequently Kepler's supposition to that effect must be rejected as chronologically unsound. Actually Donne finished the Conclave before any manuscript of Kepler's Drearm left Prague. Donne published the Conclave first in Latin, then in English. In the

Latin edition Donne said that he wanted to do no wrong to Kepplero, cui (ut ipse de se testatur) a Tycbone Brahe mortuo, cura incessit, ne quid novi in coelis se inscio existeret? In a sidenote Donne cited Kepler’s De stella . . . in Cygno, the second of three works in Kepler's New Star (De stella nova, Prague and Frankfurt, 1606). If we compare Kepler's statement of 1606 with Donne's quotation of it in 1611, we see

at once that Donne omitted the verv important word fortasse (“perhaps”). Moreover, when Donne issued Ignatius His Conclave four months later as the English translation of his Conclave Ignati, he made

another serious alteration in Kepler's statement. In his English version of the Conclave Donne said that he wanted to do no wrong “to Keppler, 1. Edward Arber (ed.), A Transcript of the Registers of the Company tioners of London, 1554-1640 Av. (Birmingham, 1894), III, 204 2. Nicolson, JH, 1:274, reptd. in Roots of Scientific Thought, p. 321.

3. Donne, Conclave Ignati (London,

4. Gesam.

Werke, I, 297:13-14.

1611), fol. Azr.

212

of Sta-

Kepler and Donne

213

who (as himselfe testifies of himselfe) ever since Tycho Braches death, hath received it into his care, that no new thing should be done in heaven without his knowledge.” 5 Donne's translation of Kepler, be-

sides omitting fortasse ("perhaps"), also be done." The combined effect of these thing quite different from what Kepler the new star in the constellation of Cygno). While Brahe was alive, Kepler

replaced existeret by “should two changes produced someactually said in his report on the Swan (De stella . . . in was "principally occupied in

calculating, since Brahe had plenty of observers, and of diligence in ob-

serving. Now that Tycho is dead, a worry took hold of me that per-

haps something new existed in the heavens without my being aware of

it. Therefore

I inspected

the stars more

frequently." 9 By

omitting

"perhaps" and inserting "should be done," Donne failed to convey to his readers Kepler's motive in shifting from calculating to observing. In considering the relationship between Kepler and Donne, we should bear in mind that in 1622, when Kepler wrote Note 8 on the

Dream, he still did not know the identity of the author of the Conclave

more than a decade after it had been published. Its anonymity was strengthened by the pretense that it was a posthumous work, although Donne outlived it by twenty years. 5. Ignatius Press, 1941), ers’ Register 6. Gesam.

His Conclave, Facsimile Text Society, No. 53 (New York: Columbia p. 3. The English version of the Conclave was entered in the Stationon May 18, 1611 (Arber, ed., III, 208). Werke, I, 297:10-14.

7. Conclave, Facsimile Text reprint, fol. Asr.

Appendix

F

KEPLER’S LEGENDARY ACCOUNT OF ARISTOTLE’S DEATH

In the town of Chalcis, which is situated in Euboea at the narrowest

part of Euripus, Aristotle’s mother had inherited estate Aristotle retired when in Athens indicted him for impiety. He against this charge “because, alluding

owned some the political did not tarry to Socrates’

property. To this opposition to him to defend himself fate and his own

danger, he did not wish the Athenians to commit a second outrage against philosophy." ? In 322 B.c., Aristotle “ended his life watching

the ebb and flow of Euripus,” about which he intended to write a book; such a closing scene would be completely consistent with the entire previous career of this extremely industrious and prolific research student: “the aged sickly philosopher, chased from his school, but still in the shadow of death pursuing his inquiries into nature’s secrets." ? What, then, was the source of the legendary tale of Aristotle's sui-

cide, referred to by Kepler in his Note 9 on the Dream? This legend began with the Exbortation to tbe Greeks, which was written by an

unknown

propagandist

for Christianity.

Together

with

other

devices

designed to turn his readers away from their pre-Christian religion, he sought to discredit the most revered pagan authors. In the present instance he ingeniously "could not understand

concocted the nature

the fable that because Aristotle of Euripus in Chalcis, he died of

grief at his great disgrace and dishonor.” This Exhortation to the Greeks was formerly attributed to Justin Martvr, a Christian author of the second century. But scholarly scrutiny of the Exhortation has shown that it is a much later work, to which the highly respected name

of Justin Martyr was attached. From pseudo-Justin the fabrication passed to Gregory of Nazianzus, an ancient town

somewhere

in eastern Asia Minor. In his First Invec-

1. Claudius Aelianus, Varia historia, iii.36; ed. Rudolph Hercher (Leipzig, 1864-66), IL, 56:2-5. 2. Ingemar Düring, “Aristotle in the Ancient Biographical Tradition,” Goteborgs Universiters Ärsskrift (1957), 63:2:188, 199, 206.

214

Kepler's Legendary tive

against

Julian,

Roman

Account

of Aristotle’s Death

emperor

(361-63)

and

apostate

215 from

Christianity, Gregory exclaimed: “You praise Homer’s curiosity regarding the Arcadian question, and Aristotle’s persistent investigation of Euripus’ ebb and flow, on account of which they died.” This linking of Homer and Aristotle makes it seem likely that Kepler had

Gregory of Nazianzus in mind when he referred in his Note 9 on the

Dream to “legendary tales.”

Nevertheless neither pseudo-Justin nor Gregory

went so far as to

make Aristotle commit suicide. Even as late as the sixth century, Procopius of Caesarea was still saying of Aristotle that, reflecting on Euripus' tides and “turning them over in his mind for a long time, he

grew deathly sick with worry and came to the end of his life.” 3 However, some silly gossip (preserved in Diogenes Laertius’ biogra-

phy of Aristotle, Lives, v.6) related that Aristotle, like Socrates, took poison after being prosecuted for impiety. This suicide theme was revived and transferred to Aristotle’s failure to understand the tides of

Euripus in the Collection and Explanation of the Stories in Gregory’s Invectives against Julian. This Collection, the earliest commentary on Gregory of Nazianzus, is attributed to a certain Nonnus, described either as a monk or an abbot, who has been assigned on stylistic

grounds to the sixth century. It was apparently this Nonnus who first

wrote, wittily and untruthfully, that Aristotle "hurled himself into this

part of the sea, saying:

'Since Aristotle

Euripus grasp Aristotle. And 3. Procopius, copius, V, 109.

Wars,

viii.6.20;

did not grasp

that is how Aristotle died." *

tr. H. B.

Dewing,

Loeb

Classical

Euripus, Library,

let

Pro-

4. J.-P. Migne, Patrologia, Greek Ser. (Paris, 1857-1945), 36:1004; 35:597, for Gregory; and 6:305 for pseudo-Justin. Anton-Hermann Chroust published "A

Brief Account of the Traditional Vitae Aristotelis," in Revue

(1964), 77:50-69.

des études grecques

Appendix G ODDUR

EINARSSON, IN ICELAND

BISHOP

In a list of Tycho Brahe’s pupils “Otto Wislandus the Icelander, a bishop in Iceland,” was rated “average as a linguist, and otherwise not

uninformed.” ! lander”

Oddur

as he was

Einarsson

usually

called

(1559-1650),

in Denmark,

or

was

“Otto

elected

the

Ice-

bishop

of

Skalholt in southwestern Iceland in 1588. He then proceeded to Denmark to be confirmed in his new office on March 25, 1589. Being inter-

ested in the mathematical sciences, he took the opportunity, before re-

turning to Iceland, to join Tycho on April 12, 1589. For on that day "Otto the Icelander arrived,” according to the entry in Brahe's Muta-

tiones

aeris

or Meteorological

Observations?

However,

the bishop

could remain with Brahe only a limited time. The aforementioned list of thirty-two pupils states that a group of nine, including Otto the Ice-

lander, “came at one and the same time; after an interval of a month or

more, having sought and obtained permission to leave, they departed." ?

Otto the Icelander's stay with Tycho in 1589 may not have been his first such visit, for in Brahe's Meteorological Observations an entry records "the arrival of Otto" on March 2, 1585.* In 1584 Otto the Icelander, the future bishop, obtained his bachelor’s degree from the University of Copenhagen. Only fourteen miles to the north lay the island on which Tycho had built his famous observatory. Does it not seem highly likely that a young university graduate interested in the mathematical sciences would

be only too happy

to pay his respects

renowned Tycho before going home to Iceland in 1586? For

Otto’s record

as a university

student,

see Holger

to the

F. Rórdam,

Kjóbenbavns Universitets Historie fra 1537 til 1621 (Copenhagen, 1868-77), II, 423, 689-90. For a general biography of Oddur Einarsson, see Finnus Johannaeus (Finnur Jonsson), Historia ecclesiastica Is-

RR

ww

m

. . . .

Tychonis Brahe . . . opera, XIV, 44:40-41. [bid., IX, 71:37, col. 2. Ibid., XIV, 44:44-45. Ibid., IX, 32:22, col. 2.

216

Oddur Emarsson, Bishop in Iceland landiae

(Copenhagen,

1772-78),

III,

332-56.

If those

217 interested

in

Otto do not enjoy reading about him in this eighteenth-century Latin written by one of his successors as bishop of Skalholt, they may prefer

to consult the Icelandic biography of Otto Biskupasögur (Reykjavik, 1903-15), I, 157-208.

in

Jon

Halldörsson,

Appendix H KEPLER’S

CONCEPT

OF

GRAVITY

Pre-Copernican thought about gravity had in the main been dominated by Aristotle’s view that “the earth and the universe happen to have the same center; a heavy body moves also toward the center of the earth, but it does so only incidentally, because the earth has its center at the center of the universe." ! When Copernicus moved the earth away from the center of the universe, he had to abandon Aristotle's conception that heavy bodies fell toward the center of the universe, because that center was no longer identical with the center of the earth. To emphasize his departure from Aristotle's theory of gravity, Copernicus declared: “For my part, I think that gravity is nothing but a certain natural striving with which parts have been endowed . . . so that by assembling in the form of a sphere they may join together in their unity and wholeness. This tendency may be believed to be present also in the sun, the moon, and the other bright planets, so that it makes them keep that roundness which they display." ? The constituent parts of each planet gathered together to form one spherical body, according to Copernicus, but none of those spherical bodies affected any other. In this respect Kepler's thinking went far

beyond Copernicus’. In the

New Astronomy Kepler defined gravity as

a "mutual corporeal tendency of kindred bodies to unite or join together.” ? Whereas in Copernicus’ conception parts of a whole united, in Kepler's theory kindred bodies unite. And for Kepler, “the moon is a body akin to the earth." * Hence, if the moon and the earth were not restrained "each in its own orbit, the earth would move up toward the moon ... and the moon would come down toward the earth... and they would be joined together." 5 1. Aristotle, On tbe Heavens, 11.14, 296° 15-18.

2. 3. 4. 5.

Copernicus, Revolutions, I, 9, Great Books, Vol. Gesam. Werke, III, 25:21-22. See Kepler's Note 62 on the Dream. Gesam. Werke, III, 25:38-40.

218

16, p. 521.

Kepler's Concept of Gravity In the New

Astronomy

219

Kepler restricted mutual

gravitational at-

traction to kindred bodies. But in his Note 66 on the Dream he did not repeat that restriction in his definition of gravity. How much did his removal of that restriction contribute to the universalization of gravitational attraction? By pushing aside the kindred bodies of the Intro-

duction to his New Astronomy, and defining gravity more generally “as a force of mutual attraction,” in his Note 66 on the Dream, Kepler

took a long stride in the direction of Newton’s universal gravitation. What was still needed was the concept that all physical bodies are akin; in other words, Aristotle’s distinction between heaven and earth had to

be swept away completely before Newtonian gravitation could be pro-

claimed. This proclamation may be regarded as a recognition of what was implied in Copernicus’ classification of the earth as a planet. In the long process of eliciting that implication, Kepler played a notable part, particularly by his more general definition of gravity in his Note 66, and by his statement in Note 202 on the Dream that “the causes of the

ocean tides seem to be the bodies of the sun and moon attracting the

ocean waters by a certain force similar to magnetism.”

But in his uni-

verse the stars remain outside the planetary realm of mutual gravita-

tional attractions, so that Kepler’s concept of gravity is not universal.

Nor did the concept of gravity enter into Kepler’s explanation of

the motion of the planets. Instead, as he wrote early in July,

1600:

In the body of the sun (whether it is at rest or itself also in motion), there is present a force which spreads out from the sun, as the force’s own dwelling-place, to all the planets and whirls them around the sun, slowly or swiftly, in proportion to the distance of each [planet from the sun]. To this general category there is only one exception, the moon,

which

revolves,

not around

the sun, like the other

five

[plan-

ets], but around the earth. And yet we cannot with good reason exempt even the moon from the moving force which is common to all

the rest of the universe. Let us therefore admit that we must seek pri-

marily in the body of the sun for the dwelling-place of the force which is the origin of the moon’s monthly motion. On the other

hand,® since all the other planets are affected by the body around which they revolve, namely, the sun, as the source of the force that moves

them, so, too, the moon

will be acted

upon

to some

is present

force

which

extent by

the body around which it revolves. But it revolves around the earth. Therefore,

in

the

earth

there

a

moves

the

moon. But, [as was said] previously, the primary origin of that force was in the sun. Therefore we have no alternative but to say that a sort of ray of moving force emerges from the sun and continues straight

ahead through the body of the earth, where Through this continuation a kind of secondary

it nests, as it were. force, as an offshoot

of that solar force, is created and persists. It spreads out again spheri-

6. Reading

Porro

instead of Porto.

220

Appendix H

cally from the earth, as its new dwelling-place, in order to make the moon revolve around the earth.” In 1600, then, Kepler believed that a solar force drove all the planets around the sun. Among the planets so driven was the earth. As the solar force passed through the earth, it left behind as an offshoot a secondary force which drove the moon around the earth. This earthforce originated in the sun, not in the earth, and was not independent

of the sun-force, which was unique of its kind. That unique sun-force

drove the planets around. It did not attract them. Nor did the planets attract the sun. There was no mutual attraction between sun and planets. But since Kepler conceived of gravity as a mutual attraction, gravity had nothing to do with the motion of Kepler’s planets. Although Kepler’s primary sun-force and secondary earth- force had nothing whatever to do with gravity, he did profoundly modify the traditional doctrine of gravity. This had interpreted the falling of a heavy body toward the earth as a “striving” on the part of the heavy body. For this striving Kepler substituted a pull, or gravitational attraction, exerted by kindred bodies on each other. The contrast between the traditional doctrine and his own conception was expressed

by Kepler in the Introduction to his New Astronomy as follows: "Rather than the stone seeking (petit) the earth, the earth attracts (trabat) the stone.” ^ Kepler's statement that the earth attracts a stone

is no casual utterance. In his Note 66 on the Dream he defines gravity as a force of mutual attraction. This attraction is no mere logical consequence of his definition; on the contrary, he presents it as a physical property of the earth, the other planets, and the bodies on them. In his Note 66 Kepler’s attention was directed to the distance between bodies as affecting the strength of their mutual gravitational attraction. In his New Astronomy, however, he had been concerned with a body’s size as governing the strength of its gravitational attraction: “Suppose that somewhere in the universe two stones were put near each other, yet outside the sphere of the force exerted by any third kindred body. Like two magnetic bodies, those stones would come together at an intermediate place. As each one approached the other, the distance traversed would be in proportion to the other's size.” ? Likewise, in the case of the moon and the earth, “on the assumption that the substance of both is of one and the same density, the earth would rise toward the moon one of the fifty-four parts of the interval be7. Gesam. Werke, XIV, 8. Ibid., III, 25:25. 9. Ibid., 25:32-36.

123:143-61.

Kepler's Concept of Gravity

221

tween them, and the moon would drop down toward the earth about fifty-three parts of the interval.” 1° The spectacular discovery announced to the world in the New

Astronomy—that

a planet’s orbit is elliptical— was first communicated

to Fabricius in a private letter in which Kepler explained:

[Gravity] is exactly the same in a big body and a small body; it is

divided according to the size of the bodies, and it receives the same

dimensions as the bodies. Suppose that a stone of a magnitude having some perceptible ratio to the size of the earth were placed behind the earth. Let it be the case that both are exempt from all other motions. Then

I say that not

only will the stone

move

toward

the

earth,

but

also the earth will move toward the stone. They will divide the intervening space in the inverse ratio of their weights. Then C being the

place where they will meet, as A [the earth] is to B [the stone] in size, so [the distance] BC will be to [the distance] CA, in exactly the same

ratio as is utilized in a balance with unequal arms.!!

In a balance with unequal arms, two unequal weights are in equilibrium when they are suspended at such distances from the fulcrum that

the product of weight times distance is equal on both sides; the smaller

weight will hang farther away from the fulcrum. Similarly, in Kepler's

theory of gravity, a big body will pull a small body a greater distance

toward their meeting-place than the small body will pull the big body.

He asserts that gravity is exactly (numero) the same in a big body and

in a small body, qualitatively, not quantitatively. Similarly he observes

the same phenomena at different times “around exactly (muero) same spot." !?

Quantitatively,

Kepler

measured

the

force

of gravitation

the

as the

product of a weight times a distance. He believed that gravitational force, like magnetic force and his solar force, was inversely proportional to the distance, diminishing directly with the simple distance," while light was attenuated with the square of the distance. How much did his speculations contribute to Newton's measurement of the gravitational attraction between any two bodies as the product of their masses divided by the square of the distance between them? 10. [bid., 25:38-41.

11. Ibid., XV, No. 358:65-75, 312, 390-91.

12. See Kepler’s Note 1 (xm) on the Geographical Appendix.

13. Gesam.

Werke, III, 237:22-24.

14. Ibid., VI, 305:23-24.

Appendix I KEPLER’S

CONCEPT

OF

INERTIA

The term “inertia” was introduced into the physical sciences by Kepler for the familiar phenomenon of a stationary body’s resistance to motion. Not only did he introduce the term, but he also extended its purview to the heavens. In Aristotle’s physics, all earthly bodies had possessed a natural tendency to move toward the place where they belonged in the universe; only when they reached their natural place did they stop moving. In Aristotle’s astronomy, on the other hand, the celestial spheres had had a natural tendency to revolve forever. Hence, it was a decisive departure from tradition when Kepler declared in the

New Astronomy that “the planetary globes must be material by nature

because, from the beginning of things, they have possessed an inherent propensity for rest or absence of motion.” ! On account of the planets’ propensity for rest, Kepler concluded in 1609, a continuous force was needed to keep them moving: “For my part I say that the planetary globes are so constituted that, wherever they are encountered in the

heavens, they would stand still if they were not driven forward.” ? In his Epitome he included a comprehensive application of Keplerian inertia to the heavens:

A celestial body . . . because it 1s material, is naturally incapable of moving from place to place. It has a natural inertia or quiet, on account of which it remains stationary wherever it is located in isola-

tion. To move it from its position and its state of rest, there must be a

force, which 1s something bigger than its matter and bare body, and

which overcomes its natural inertia. . . . If there were no inertia in a

celestial body's matter, which

is its weight, as it were, no force would

be needed to move the body. And if even the smallest force were assumed to move it, there would be no reason why the body should not revolve in an instant. But since the revolutions of the spheres

occur in definite times, longer for one planet, shorter for another, it is therefore apparent that the inertia of matter is not related to the moving force as zero is to a positive quantity. Hence it is not true that 1. Gesam. Werke, III, 244:19-21.

2. Ibid., IV, 192:38-41.

Kepler’s Concept of Inertia

223

there is no inertia and resistance on the part of celestial matter.

.. .

On account of this inertia of matter it happens that any body, wherever

it 1s located

in the

universe

beyond

the

range

of propelling

forces, is naturally at rest in that place, because matter as such has no faculty of moving its own body from place to place.? In a sharp rejection of the older celestial view, Kepler said: The planetary bodies moving or revolving around the sun must be considered,

not

as

mathematical

points,

bodies having, as it were, a certain weight

but

obviously

as

material

. . . that is, insofar as they

are endowed, in proportion to the bulk of their bodies and the density of their substance, with the capacity to resist motion imparted to them from without.*

While this aspect of the inertia principle was formulated by Kepler

with admirable clarity, he did not stop there. In the New Astronomy he asserted that "from the soul of anyone who throws pebbles an emanation of motion adheres to the pebbles, by which they are carried forward, even when the thrower has taken his hand away from them." 5 Kepler did believe, then, that a motion, once it was imparted to a

body, persisted in that body after it had ceased to be in immediate con-

tact with whatever continuing motion motion is attributed an innate inertia. However, Kepler text of the Dream,

had initiated the motion. But here the cause of the is not yet mechanical, and the persistence of the to an emanation imparted from the outside, not to advanced far beyond this stage of thought. In the p. 16, above, he says that "finally the bodily mass

proceeds toward its destination of its own accord" (sponte sua). Here a motion, once initiated, continues as a result of something internal,

and without the help of an external force, whether mechanical or not.

Nor is this an isolated utterance. For in his Note 75 on the Dream,

when the external forces affecting the moving body cancel each other

out, "the body itself as a whole propels its limbs." 'The motion in the

text of the Dream is maintained without a cause, since it proceeds spontaneously, "of its own accord." Although Kepler did not attach the label “inertia” to this spontaneous continuation of motion, his Dream may well have dropped a seed in the fertile brains of those who saw that inertia includes perseverance in a state of motion as well as in a state of rest. 3. Ibid., VII, 296:30-297:31; Great Books, Vol. 16, pp. 894-95. 4. Gesam. Werke, VIII, 94:9-14. 5. Ibid., II, 242:15-17. 6. Edward Rosen, “Kepler’s Harmonics and His Concept of Inertia,” American Journal of Pbysics (1966), 34:610-13.

Appendix J THE

COLD

OF

QUIVIRA

Kepler’s reference in the text of the Dream to the low temperature of the moon’s Privolvan hemisphere as “cold more unbearable than the Quiviran” rests on a misconception of North American geography.

The Spanish explorer, Coronado, and his companions were misled by

an Indian interpreter “whom they named the Turk, because he looked like one.” His numerous lies included the prediction that “gold and sil-

ver would be found” in a place called Quivira (as the Spaniards, per-

haps assimilating river, understood

the the

Indian name).

term to Guadalquivir, Spain’s mighty When Coronado wrote a letter to his

king on October 20, 1541, he located Quivira “at a latitude of forty

degrees” and reported that “the soil itself is the most suitable that has been found for growing all the products of Spain.” ?

Since Quivira ? (which has since been identified with what is now central Kansas, then inhabited by Wichita Indians), resembled Spain, why did Kepler regard it as the coldest place on earth? Perhaps Coronado's statement that “the land is so cold . . . that it seems impossible for one to be able to spend the winter here” was misapplied to Quivira, although Coronado plainly intended it for another region. One of his companions wrote: “As the ice in the river was thawing, after being frozen for almost four months, during which it was possible to cross over the ice on horseback, the departure for Quivira was arranged." ?

By a second misunderstanding, "European map makers absurdly re-

versed the direction of Coronado's long eastward march . . . and then shifted the province of Quivira to the shores of the Pacific Ocean.” 4 I. George P. Hammond and Agapito Rey (eds), Narratives of tbe Coronado Expedition 1540-1542, Coronado Cuarto Centennial Publications, 1540-1940, II (Albuquerque: University of New Mexico Press, 1940), pp. 219, 234, 189. 2. Coronado's expedition to Quivira was recently narrated by Stephen Clissold,

The Seven Cities of Cibola (New York: Potter, 1962), pp. 131-70.

3. Hammond and Rey (eds.), Narratives of the Coronado Expedition, 234. 4. Herbert E. Bolton, Coronado on tbe Turquoise Trail (Albuquerque:

224

pp.

190,

Univer-

The Cold of Quivira

225

Two of Kepler’s favorite geographers, Ortelius and Mercator, placed the kingdom of Quivira on the northwest coast of America close to the northeast coast of Asia. The cold Siberian winds blow from the northeast into central Europe. Hence we can understand why Kepler told Fabricius: "I believe that in a previous letter I wrote about the cold on the shores of Quivira. That seems to be the region whence we receive the northeast wind, which is always cold. Consequently in that place there is an anus of the universe, from which such cold winds come." 5 In the previous letter Kepler had written: "In North America, it appears, the cold is so great that there must be exhalations, like those which occur among us sometimes in the summer. That is the region from which the cold northeast wind comes to us." 9 The region which Kepler, misled by the mapmakers, had in mind as the coldest on earth was, then, this northern Quivira. If our reconstruction has not gone astray, the last two syllables of Guadalquivir, derived from the Arabic word for “great,” were transformed by a series of steps in this comedy of errors into Kepler's designation of the cold anus of the universe. He was evidently unfamiliar with the correct characterization of Quivira as a "temperate land." * sity of New Mexico Press, 1949; reprinted, 1964, under the title Coronado, Knight of Pueblos and Plains), p. 398. 5. Gesam. Werke, XV, 268:1126-28; for Quivira in northwest America, see the maps of the earth and the New World in Ortelius, Theatrum, fols. 1-2. 6. Gesam. Werke, XIV, 433:976-78. 7. Francisco López de Gömara, Historia general de las Indias (Saragossa,

1552-53, Pt. I, fol. 116r; reprinted, Madrid and Barcelona, 1932, II, 236).

Appendix K DAVID

David

Fabricius

FABRICIUS

(1564-1617)

started a new

branch

of astronomy,

the study of variable stars, by an investigation which he reported privately to Tycho Brahe. The latter incorporated in his handwritten

Treasury of Observations a series of reports from Fabricius, including the following: Observations

of a Certain

Supplementary

Star

in the Constellation of the Whale

Which

in '96

Appeared

In the morning of August 3 of the aforementioned year I was going to observe Jupiter and its distances from the more prominent stars in its vicinity (for on account of the summer air and the dawn the

smallest stars were barely visible). As I was about to observe with my

instrument,

I noticed

toward

the south

in the

constellation

Whale an unfamiliar star not seen before in that place magnitude. As I inspected it carefully and thought about was immediately struck by the idea that a new comet thereupon examined my celestial globe, and consulted [Tables]

of the

and of that its position, I had arisen. I the Prussian

catalogue of stars to see whether a star of that magnitude

was perhaps recorded there. But I found nothing agreeing with the position, much less with the observed magnitude. . . . The distance between Jupiter and the bright I designated the new star, since around 20? 22"... . This star bigger than the bright star in

star toward the south (for that is I knew nothing definite about it) is of the second magnitude, a the Ram [a Arietis, which was

assigned to the third magnitude]

and ruddy

I could not discern any change

from

how was little then

like Mars. . . . After

August 21 I no longer observed its position with instruments, because

the preceding

observations.

Nevertheless, I saw the aforesaid star thereafter several times until the

early days of September, but almost every day it became smaller. . . . ] undertook to gauge its magnitude by the brilliance of Jupiter.

. . . Maybe

I was not concerned with an actual fixed star...

. The

air was hazy almost continuously for several weeks at that time. . . .

If these

observations

of the

supplementary

star should

be

such

as

could confirm your opinion [that changes occur in the starry heavens], I would certainly be delighted. . . . I attest that I have reported nothing, not one jot or one tittle, other than what I observed.!

i. T ycbonis

Brahe

. . . opera,

XIII,

114-15.

226

David Fabricius While

Brahe

was

still in his native

Denmark,

227 he

sent Fabricius

a

copy of his Astronomical Letters (Epistolarum astronomicarum liber primus, Uraniborg, 1596).2 When the great Danish astronomer went

into exile at Wandsbek, he was visited by Fabricius, to whom he gave

instruction and one of the advance copies of his Progymmnasmata or Preliminary Exercises, Part 1.3 After Brahe moved on to Bohemia, Fabricius undertook what he called an “astronomical

journey,” which

included further conversations with Brahe.* But his hopes of talking also with Kepler went unfulfilled because the latter was away on per-

sonal business, and Fabricius could not wait for him to return.? Sorely

disappointed by his failure to meet Kepler face to face, on June 23, 1601, Fabricius wrote

him a

letter, thereby initiating a lengthy and

voluminous correspondence. Published completely for the first time in

Gesammelte

Werke, this interchange proved to be both terribly irk-

some and immensely valuable to Kepler. In one of his numerous letters Fabricius reported

to Kepler

his ob-

servations of the new star of 1604. This nova reminded Fabricius that “also in '96 on August 3 I saw a new star of the second magnitude in 25° 47’ of Aries with latitude , which disappeared in October.” ® When Fabricius wrote this letter, he must have been in even more than his usual hurry, since he dispatched

it without remembering

to insert

the latitude of Mira Ceti (as the variable star which he discovered was later christened).

In this same letter Fabricius asked for a copy of Kepler’s Optics, if the book was already off the press.” Kepler complied, calling Fabricius’ attention to some errors left uncorrected by the "Catalogue of Errors"

at the end of the Optics.® Fabricius gratefully acknowledged receipt of

the book.? He saw that Kepler had inserted the following statement in

the supplementary Notes added during the process of proofreading:

“David Fabricius sent to Brahe certain observations which he had made

in Friesland while measuring the distance of Mercury from a

certain

bright star in the Whale. That star could not be found anymore, by Fabricius or by anyone else.” !? Aware 2. Gesam. Werke, XV, 121:242-43. 3. Tychonis Brahe... opera, VIII, 306:27-29, and XV, 10:133.

4. Gesam.

AN

ON

. Ibid., 59:28-30. . Ibid., 62:172-73, 79:35-39.

. Ibid., 115:6-7. 10. Ibid., II, 376:3-6.

DD

182:39-183:2;

Werke, XIV, 220:44-45; cf. XV,

. Ibid., XIV, No. 193:2-10. . Ibid., XV, No. 297:22-24.

of the conflict between Kepler

119:158.

Gesam.

Werke,

XIV,

228

Appendix K

and Brahe’s heirs over access to Tycho’s unpublished papers, Fabricius sent Kepler the following summary of his original report: In order that you may have some precise information about that star of '96, I append the observations which I transmitted some time ago to Tycho.

Early in the morning

observing Jupiter. Toward the south little bigger than the three stars in Arietis] and was of a reddish color. Aries, 15? 54%2’ south latitude [here

of August

3, '96, old style, I was

I saw a bright star, which was a the head of the Ram [a, B, y . . . Its position was 25? 47' of Fabricius fills the gap which he

had left open in his previous letter]. . . . It was of the second magni-

tude. Note that these observations are exact. After Michaelmas [September 29] the star disappeared. At that time I had not formed any

friendship with Tycho or other astronomers.!!

This last remark explains why Fabricius’ observations of Mira Ceti in

1596 were not communicated

to Brahe immediately. In the Optics, it

will be recalled, Kepler said that Fabricius measured the distance from

Mira Ceti to Mercury. Since Mercury was quite remote from Jupiter on August 3, 1596, when Fabricius discovered Mira Ceti, the distances

from the variable star to the two planets were very different. Yet Fabricius failed to call Kepler’s attention to this substitution of Mer-

cury for Jupiter, although as a rule he did not hesitate to correct Kep-

ler’s slips.

In the summer of 1607, Fabricius received from Kepler a copy of

the New Star as a gift. "I read and perused it with the greatest pleasure," he told Kepler.!? It narrated Fabricius’ discovery of Mira Ceti as

follows: “. . . in the morning . . . of August 3/13, 1596 . . . David Fabricius . . . discovered a new star of the third magnitude in 25° 45’ of Aries, 15? 54' south latitude, which disappeared after October of

the same year.” !? In his report to Brahe, and in two of his letters to Kepler, Fabricius had invariably classified Mira Ceti at the time of its discovery as a star of the second magnitude. The effort to determine the exact times when Mira Ceti attained the second magnitude, its maximum brightness, is not helped by Kepler's gratuitous substitution of

the third magnitude for the second. But this discrepancy in magnitude,

if Fabricius noticed it at all, must have dwindled to nothing in his eyes, dazzled by the Imperial Mathematician's glowing tribute to him in the New Star: '"Thoroughness in observing the heavens began with Brahe.

After it died with him, supreme authority in observing has rested with rt. Ibid., XV,

117:64-77.

12. Ibid., 477:8-9. Kepler's presentation copy of the New Star was preempted by the heads of the East Friesland government, so that Fabricius had to borrow another copy while waiting for his own to be returned (bid. XVI, 123:10-14). 13. Ibid., I, 259:10-15.

David Fabricius

229

Fabricius. This prize is awarded to him very cheerfully by me, greatly

impeded as I am by distorted vision. Moreover, in investigating the motions of the planets he has a most ingenious mind, and in his think-

ing he shows indefatigable zeal.” 14 This magnificent eulogy was emphasized

by

the

following

sidenote:

“David

Fabricius,

a

diligent

astronomer.” Fabricius thanked Kepler for presenting him with a copy of the New Star, “especially because of your laudatory reference to

me in that book.” 4 Equally warm-hearted

Astronomy

praise

was

lavished

by

Kepler

in his New

on “David Fabricius, the diligent cultivator of astronomy

in East Friesland,” whose observations were transmitted to Kepler and

used by him “because since Brahe’s death very few observations have

been made by me, and they have not been made on consecutive days.” *° In the New Astronomy Kepler destroyed the ancient prejudice that the heavenly bodies must move in paths compounded of circles by announcing that the orbits of the planets are elliptical. With reference to this law, his greatest contribution to science, he said that Fabricius

"very nearly anticipated me in discovering the truth.” !* In his last letter to Kepler, dated March

12, 1609, Fabricius wrote:

On February 5 I was observing the approaching conjunction of Jupi-

ter

and

Mars.

In

the

Whale

immediately inspected. When

I noticed

an

unfamiliar

star,

which

I examined the distances on a [celestial]

1

globe, I found them to agree with the position indicated on the globe for the star which I observed in August and September of '96. Since

that time I had not seen that star. An amazing phenomenon! God is my witness that I saw and observed it twice at different times. It is noteworthy that Jupiter had come to nearly the same position in the Ram as it had occupied in '96. . . . Hence you see, my dear Kepler, that my opinion about new stars and comets is truc: they are not created afresh, but are only

deprived of light from

time to time.

. . . At

the end of February I still saw it and observed it very clearly. Now, on account of the hazier sky and the [star's] proximity to the horizon as well as the moon's light, I have not been able to catch a glimpse of it. May I ask whether you, too, have seen it or have heard that anybody has observed it? I am eager to learn vour opinion about these matters. An amazing phenomenon and true! Its position (as I indicated in my German treatise on the new star) was 25? 47' of Aries and 15° 54’ south latitude.!$ 14. Ibid., 210:35-211:1. 15. Ibid., XVI, No. 481: 14-17. 16. Ibid., III, 148: 3-6. 17. Ibid., 345:13-14. For an excellent monograph on the founder of the study of variable stars, see Diedrich Wattenberg, David Fabricius (Berlin-Treptow, German Democratic Republic, 1964; Vorträge wnd Schriften der ArchenholdSternwarte, No. 19). 18. Ibid., XVI, No. 524:265-84.

230

Appendix

K

This letter was never answered by Kepler. He broke off his corre-

spondence

with

bringing out his

Fabricius

mainly

because

he was

busily

New Astronomy, as he later explained.’

Nevertheless, the part of Fabricius’ last letter which

engaged

in

dealt with Mira

Ceti was quoted by Kepler in his Answer to Röslin (Praguc,

1609).”°

Here Kepler published Fabricius’ statement that he had not seen Mira

Ceti between 1596 and 1609. Yet on November 30, 1607, Kepler wrote

to a critic of Fabricius that according to the Frisian astronomer Mira Ceti “has disappeared again.” ?! Fortunately Kepler committed this error in a private letter, and therefore it has caused less confusion in

the study of Mira Ceti than his substitution of Mercury for Jupiter in the Optics, and of the third magnitude for the second magnitude in the

New Star. Fabricius was

thoroughly

incensed

because,

no matter

what

strata-

gem he resorted to, he could not induce Kepler to resume their private correspondence. Hence, in his Prognostications for the years 1615, 1616, and 1617, Fabricius addressed public interpellations to Kepler. To

these

interpellations

Kepler

responded

equally

publicly

in

his

Epbemerides.?? On the title page of that work he announced that he

was "answering the numerous interpellations of David Fabricius, the Frisian astronomer.” ?? Kepler dated this reply October 1, 1616,?* but

it was not printed until March, 1618.75 Hence it was never seen by Fabricius, since the poor man was murdered on May 7, 1617.

In the Ephemerides

Kepler turned

Fabricius' son, Johannes, with whom

tive correspondence ?? than

with

to the distressing subject of

Kepler had carried on a

his father:

“Having

learned

less ac-

of his

premature death by reading about it in your Prognostication for the year 1618, I make a public avowal of my grief. For I am aware that you, dear dent of thought, tle book

friend, have lost in your son a valiant and highly expert stuscience, who was passionately devoted to truth and free while I have been deprived of my heart's delight. But the liton sunspots which he published in 1611 is without the least

question still alive. Conferring a greater honor than any epitaph or funeral oration,

it contains

a guarantee

the solace of our common grief." ?

of his posthumous

19. 20. 21. 22.

Ephemerides, p. 16:15-17; Frisch, II, 109:20-26. Gesam. Werke, IV, 104:9-15. lbid., XVI, 86:111-12. Ephemerides, pp. 16-24; Frisch, II, 109-17.

24. 25. 26. 27.

Ephemerides, p. 24:last line; Frisch, II, 117:20 up. Caspar, Bibliograpbia Kepleriana, p. 71. Gesam. Werke, XVI, Nos. 485, 509. Epbemerides, p. 17:16-20; Frisch, II, 775:last eight lines.

23. Frisch, VII, 479:17-18.

fame,

and

David Fabricius Kepler’s expression

of condolence

and

231

sorrow

was

no

mere

indul-

gence in sentimental exaggeration for the purpose of consoling a heartbroken father. The posthumous fame of Johannes Fabricius is indeed guaranteed by his little book, published when he was only twenty-four

years old, because it was incontrovertibly the earliest announcement in print that sunspots had been discovered.

Was Johannes Fabricius also the first to detect sunspots, as Mastlin

thought? ?8 Conflicting claims to that distinction were advanced on behalf of several astronomers. The ensuing bitter quarrel was partly responsible, in the opinion of some scholars, for the charges of heresy that were brought against Galileo and resulted in his condemnation and imprisonment. This acrimonious debate broke out after the publication

of Johannes Fabricius’ book, the dedication of which is dated June 13, 1611

(De maculis in sole, Wittenberg,

1611, fol. A4r).

But

the exact

date of Johannes Fabricius' discovery of sunspots is not indicated in his book.

The

priority controversy

having

become

a public

issue, David

Fabricius issued the following statement in his Prognostication for the year 1615 (fol Asr): "At the present time spots or black splotches

have actually been perceived and observed on the sun. Such were detected for the very first time by my son, Johannes Fabricius, student of medicine, in my presence on February 27, 1611, old style, through

the Dutch glasses." David Fabricius’ Prognostication for the year 1615

is an exceedingly rare book.

A copy of it was found

and republished

by Gerhard Berthold, in David Fabricius und Johann Kepler, Vom neuen Stern (Norden and Norderney, 1897), from which the quoted passage was reprinted in Gesam. Werke, XVII, 450.°° It has been contended that Johann B. Cysat (1588-1657) anticipated Johannes Fabricius in the discovery of sunspots by exactly three days.

This contention was first published more than two hundred years after the event, and it is allegedly based on a Cysat manuscript that has disappeared. According to this extremely belated report of a vanished manuscript, the morning of March 6, 1611 (new style), was so cloudy that Cysat was able to examine the sun directly through a telescope and

discover the sunspots. But, strangely enough, no equally cloudy day came along again for more than half a year (when Fabricius’ book was announced for the autumn Frankfurt book fair). Then several days in

a row were cloudy, after which to make daily observations.9?? 28. Gesam.

alternative methods

permitted

Cysat

Werke, XVII, 56:114-16.

29. Johannes Fabricius first saw the sunspots in February, 1611, more than three

months

before

he dated

the

dedication

of his book

in June.

He

discovered

the

sunspots while trying to verify the irregularity of the sun’s limb, as reported to him bv his father in a letter (De maculis in sole, fol. C2v). 30. This account

of the discovery

of sunspots will be found

in Zinner, Entste-

232

Appendix K

Credit for first observing sunspots was

given to the Fabricius

team

of father and son by Simon Marius (Mayr) in his Prognostication for 1613.31 In his World of Jupiter (Mundus Jovialis, Nuremberg, 1614),

as an experienced controversialist, Mayr said: “The discoverers and first observers of sunspots are the Fabricius team, father and son. But their names are suppressed because they are regarded as heretics.”

Mayr made this statement on fol. G4v in an epilogue addressed “To

the Fair-Minded Reader,” which he added in the second edition of his

World of Jupiter.??

bung und Ausbreitung der Coppernicanischen Edward Rosen, Isis (1946), 36:261-66.

31. Reprinted

by Josef Klug,

“Simon

Lehre,

Marius

pp.

346, 495-96;

aus Gunzenhausen

review

und

by

Galileo

Galilei,” Bayerische Akademie der Wissenschaften, Abbandlungen, math.-phy. Klasse (1906), 22:524. 32. The first edition was translated into English by Arthur Octavius Prickard, Observatory (1916), 39:367-81, 403-12, 443-52, 498-503.

Appendix L PAUL

Paul Guldin

(1577-1643)

GULDIN

carried on an extensive

correspondence

with Kepler. ‘The exchange was begun by Guldin, who inserted a note

in a letter addressed to Kepler by a colleague at the Jesuit University of Graz, where Guldin taught mathematics from 1616 to 1619.1 In his reply to this first note, Kepler mistakenly called Guldin “John” instead of “Paul.” 2? Guldin left Graz in 1619 for reasons of health. Having completed his convalescence, he went to Vienna, where he resumed the teaching of mathematics in November, 1621. For the next six years he was professor of mathematics at the Jesuit University of Vienna. Hence, when Kepler sent the letter which forms the Geographical Appendix to the Dream, after July 17, 1623, it was addressed to Guldin in Vienna, not in Graz. Early in 1626, while him from Linz:

Guldin

was

still in Vienna,

Kepler

wrote

to

I am not sending you the two books by Snel because the Reform

Commissioners,

through

the dean

and secretary, who

have been

dele-

gated to get rid of heretical books, have as a general rule locked up

the books of all those living in the Palace of the Province.® Accordingly my whole library, with the exception of a very few books pertaining to the exercise of my profession, has been locked up since onm

. Gesam. Werke, XVII, 259: 1-3.

un

bwM

. Ibid., 260:38. . See Kepler’s Notes on the Geographical Appendix, fn. 2o. . See fn. 11, below, and Kepler’s Geographical Appendix, fn. 2.

. See Kepler’s Notes on the Dream, fn. 331. In a previous letter to Guldin, Kep-

ler had said that he had two copies of Snel's Hessian Observations and Description

of the Comet of 1618 (Gesam.

Werke, XVIII, 254:58-60).

6. In this Palace of the Estates of the Province of Upper Austria a room was assigned to Kepler, the Province’s Mathematician, on September 19, 1625; the official assignment was excerpted from the archives by Hanns Kreczi, “Johannes Kep-

ler in Linz,” in Bilder aus vergangenen Tagen, Linzer Reibe (Linz, 1947), p. 84, n. 8o. The history of the domus provincialis, as this superb monument of Renaissance architecture was called in Latin, or “Landhaus,” as it is called in German, has been

written, so far as records surviving from the disastrous fire of 1800 permit, by Eduard Strassmayr, Das Landhaus in Linz (Linz, 1950).

233

234

Appendix L December 31.7 To be sure, they offer to open up my library to me, on

the condition that I myself be willing to choose the books to be surrendered. In other words, the bitch is ordered to give up one of its pups. The infamy of such thoroughgoing subjection is so painful that I prefer to stand aside and watch and talk to them while they make the selection. Since I have few books, there is scarcely any with which

I would not lose something from my studies, on account of the daggers, fingers, hands, curved lines, and notes which I have written in

them. ... As soon as my little library is released, I shall let you see the two

books by Snel. Perhaps you shall have them, for one of the officials at Vienna is asking me for them. I shall write to him about them and your request.®

Did Guldin's request to borrow

two of Kepler's books affect the

sequestration of Kepler's library? Kepler told Guldin: "I recently talked about this matter to Father Keller, in the hope that he would

intercede for me in your name; but contrary to my hope, I found him

harsh and surly."? Four months after Kepler had been denied all access to his sequestered books, he stated: "My library is still sealed up in the daytime.” 1°

In 1623 Guldin had been appointed procurator of the Austrian province of the Jesuits,! a responsibility he was relieved of in 1632 at his

own request. The Bohemian province was split off from the Austrian province in 1622, and the procurator of the newly created Bohemian

province of the Jesuits was George van der Boon.!? In Kroess's history of the Bohemian province of the Society of Jesus, Guldin's name does not even appear.

All the letters of Guldin to Kepler have disappeared, with a single

exception. Even this exception is only apparent, since it is actually a document drafted for Guldin, which he incorporated in a letter of his 7. Kepler's a Prid. Cal. Jan. means "December 31," 1625. 8. Gesam. Werke, XVIII, No. 1024:25-35, 54-56. 9. Ibid., 258:42-44. 10. Ibid., 260:14-15. r1. Bernhard Duhr, Geschichte der Jesuiten in den Ländern deutscher Zunge (Freiburg im Breisgau, Munich, and Regensburg, 1907-21), 2:2:433. Duhr’s tanta-

lizingly incomplete statement about Guldin’s activities was kindly supplemented

for me by Father Joseph T. Clark, S.J., of Canisius College, Buffalo, New York, and his Roman agent, Father Mario Colpo, S.J. By utilizing the unpublished cata-

logues of all Jesuit personnel present within the boundaries of the Austrian province during the years of Guldin’s movements (Austria, 123, fols. 315r, 362r), they

decisively placed Guldin in Vienna, not in Graz, when Kepler wrote him the letter which forms the Geographical Appendix to the Dream. 12. Alois Kroess, Geschichte der böhmischen Provinz der Gesellschaft Jesu, Vol. II, Pt. 1: Quellen und Forschungen zur Geschichte Österreichs, XIII (Vienna,

1927), PP. 74, 95-

Paul Guldin

235

own to Kepler, dated March 29, 1628. In this letter Guldin referred to

two lines !? in a prior letter to Kepler, which must have been written between October 1, 1626, and February 24, 1628. Those two lines in the lost letter apparently attempted to persuade Kepler to follow the

example of Guldin, a convert to Catholicism, by joining the Church of Rome. Rather than surrender his principles, Kepler steadfastly replied:

"lam prepared to give up not only the rewards which are now dangled

before me with His Imperial Majesty’s most gracious and most generous consent, but also the Austrian region, the entire empire, and

what is more serious than everything else, astronomy itself; I would

add even my life.” 14 In 1616 the Roman Catholic Church suspended Copernicus’ Revolutions “until corrected,” and admonished Galileo to abandon Copernicanism.!5 Federico Cesi, one of Galileo’s friends in Rome, was visited soon thereafter by Guldin. “He showed great affection for you," Cesi told Galileo, “and disgust at the outcome of the recent proceedings." ! The priority in the discovery of sunspots having been claimed publicly by a fellow-Jesuit, Christopher Scheiner,"" Guldin told Giovanni Pieroni, the Imperial Architect, privately “many times that he remembers, with the utmost certainty with which a human being can say he remembers anything, that he was the first who informed Father Scheiner that spots were seen in the sun.” 1?

Even

heretic

after Galileo

and

sentenced

had to

been

condemned

life imprisonment,

by

the Inquisition

Galileo’s

name

was

as a in-

scribed by Guldin in a copy of his most important publication, and he

gave this copy Arcetri.” 19

to

Pieroni

to

be

sent

to

Galileo

in

his

“prison

at

13. Gesam. Werke, XVIII, 340:2, 355:41-42.

14. [bid., 333:107-10.

15. See Kepler's Notes on the Dream, fn. 34.

16. Galileo, Opere, XII, 285:14-16.

17. In his Rosa Ursina (Bracciano, 1626-30) Scheiner claimed that he had anticipated Galileo in the discovery of sunspots. Scheiner based this claim on observations which he had made in the month of March, 1611 Galileo, Scheiner evidently felt that the month of March

(ibid., p. 6). As against was early enough, with-

out the necessity of specifying any particular day. However, as against Johannes

Fabricius, who is completely ignored in the Rosa Ursina, a day early in March

was

needed. This awkward gap in the Rosa Ursiza was deftly filled in the vanished manuscript of Scheiner's associate, Cysat (see Appendix K).

18. Galileo, Opere, XVI, 189:36-39. 19. Ibid., 391:36; XVII, 193:15-18.

Appendix THE

In his Note

PEOPLE

220 on the Dream,

OF

LUCUMORIA

Kepler refers to the supposed

resur-

rection of the people of "Lucumoria."! In his earlier work (Tertius interveniens, 1610) he had previously remarked that “in the Muscovite

region there is said to be a race of people who die out completely in the winter, when they are entirely deprived of the sun, and revive in the spring.” 2 Kepler took this statement from the Jesuit theologian, Rio, who reported that “in Lucomoria, a district of Russia, certain people live who die every year on the twenty-seventh day of the month November, as swallows and frogs are in the habit of doing, on account of the intensity of the winter cold; afterwards, when spring returns, on the twenty-fourth day of April they are restored to life again." Rio went on to say that when the people of Lucomoria “feel that death is threatening them, they put their merchandise in certain places. . . . This merchandise is taken away by the neighboring peoples, who i in the meantime leave their own merchandise of equal value in the same place. If this merchandise is deemed to be a fair exchange by the Lucomorians when they revive, they accept it as their own. But if not, they try to recover their original merchandise. This is said to be the cause of the very frequent quarrels and wars between them." Rio's concentration on the struggle over material possessions is replaced in Kepler by concern over possible harm due to the temporary absence of the soul. This substitution provides an excellent example of Kepler’s frequent practice of embroidering his sources, just as his garbling of the name of the district shows that, like most of his contemporaries, he did not always take the trouble to verify his quotations.

Rio explained

that he copied his resurrection story from

1. See Kepler’s Notes on the Dream, fn. 358.

a descrip-

2. Gesam. Werke, IV, 201:18-21. 3. Martin del Rio, Investigations of Magic, Bk. IT, Question 29 (ed. Kóln, 1633, p. 310).

236

The People of Lucumoria tion of Muscovy

an Italian who

by “Guaguin.”

Alessandro

enlisted in the Polish army

237

Guagnini

(1538-1614),

and rose to be an infantry

commander, published a Description of European Sarmatia (Sarmatiae

Europeae descriptio, Krakow, 1578). In the section entitled “Description of Muscovy”

(folio 15r) Rio found the resurrection story. But

Guagnini labeled it an “incredible tale.” This healthy skepticism ished when Rio repeated the rest of the tale told by the soldier.

van-

Rio added that the same tale was told in a book about Muscovy by an author whom he calls “Sigismund the free baron.” Sigmund von

Herberstein (1486-1566), the first member of his family to be granted the title “Freiherr,” was the Holy

Roman

Empire’s ambassador

to the

czar of Russia, and the author of Commentaries on Muscovite Affairs (Vienna, 1549). From this work, the earliest authentic and substantial

account of Russia, without any acknowledgment, Guagnini borrowed the resurrection story. Guagnini made only three changes in Herberstein’s version. To the ambassador's frogs Guagnini added swallows, a bit of animal lore which need not detain us. Much more important than Guagnini's addition to Herberstein are his two subtractions. Where Herberstein spoke of the Lucomorians' "fixed time for dying or sleeping," Guagnini suppressed the suggestion of hibernation. He also deleted Herberstein's characterization of the resurrection story as “just like a fable." This judgment of Herberstein was repeated by Rio as the opinion of "Sigismund the free baron," identification of whom would have presented much less of a puzzle to Kepler than to other readers of Rio. The Herbersteins were the leading noble family in Graz, where Kepler

spent six eventful

years.

He

dedicated

his Cosmographic

Mystery,

which he wrote while he was living in Graz, principally to "Sigmund Frederick, the free baron of Herberstein." > This Sigmund Frederick,

Freiherr von Herberstein (d. 1621), was not the son of the Sigmund Herberstein who wrote the Cozezmentaries on Muscovite Affairs. That

Sigmund, although married, was childless. The two Sigmunds belonged

to different branches of the same Herberstein family, which enjoyed great renown throughout Austria. Kepler with the older Sigmund Herberstein's book.

was For,

personally familiar with regard to the

geography of Russia, Kepler savs: "I trusted the measurements of the 4. Rerum Moscovitarum commentarii, ed. Basel, 1551, p. 86; English translation by R. H. Major, Notes upon Russia, Hakluyt Society, 1st series, Vols. 10 and 12 (London, 1851-52; reprinted, New York: Franklin, 1963), II, 40. 5. Gesam. Werke, I, 5:2-3. 6. See Ersch and Gruber, Allgemeine Encyklopädie, Section 2, VI (Leipzig, 1829), 109, 117, IIQ.

238

Appendix

distances which appear in Sigmund

M

Herberstein.” 7 Hence there can be

no doubt that Kepler recognized Rio’s “Sigismund the free baron” as his fellow-townsman of Graz. Did Kepler disregard Herberstein’s candid avowal of the reason why he incorporated into his book material which he himself did not be-

lieve? Herberstein had been given an itinerary, about which he says: “Whatever I have reported up to now has been literally translated by

me from a Russian travel book, which was offered to me. Among these reports, some seem to be legendary and scarcely credible, for instance, the one about men . . . who die and return to life. . . . Al-

though I myself have carefully investigated these reports, I have been unable to learn anything

definite

from

anybody

who

has seen

these

things with his own eyes (although everybody said they were true).

Nevertheless, in order to afford others an ampler opportunity to investigate these matters, I decided to omit nothing." 5 Presumably Kepler noticed this passage, and paid no attention to it. For an understanding of his mentality, it is valuable to contrast his attitudes toward two aspects of Herberstein's book. On the one hand, he trusted its measurements of distances. On the other hand, he chose to ignore its skeptical comment, as quoted by Rio, about the resurrection story, which Kepler repeated without any reservations. This kind of tale unquestionably appealed to one side of his personality. Nor should we ever forget that he did not plan to become an astronomer. His first choice of career was the clergy, and his training was in theology, which inculcates belief in the existence of various beings without ad-

ducing tangible evidence of the sort demanded by a thoroughly scien-

tific mind.

Kepler himself said about Fabricius: “He is a theologian, and there-

fore more favorable to doctrines for which no cause can be assigned." ? What is here translated "for which no cause can be assigned" is a

single Greek word (anaitiologetous). The exactly opposite Greek word (aitiologetos) was prominently placed by Kepler on the title page of his New Astronomy, in which the Causes are Investigated, or Physics of tbe Heavens.!° A novel feature of his astronomy, Kepler was aware, was his introduction of physical causes to explain the motions of the heavenly bodies. Despite this immense

contribution

to the

advancement of science, Kepler still retained traces of the mental attitude which

he noticed

in his theologically-minded

friend,

7. Rudolphine Tables, precepts, p. 39; Frisch, VI, 558:11-9 up.

8. Rerum Moscovitarum commentarii, ed. 1551, pp. 86-87. 9. Gesam. Werke, I, 248:28-29.

10. Ibid., II, 5.

Fabricius.

The People of Lucumoria

239

He had told Mästlin, in connection with what he regarded as the great discoveries in his Cosmographic Mystery:

When these have been published, perhaps other persons will make additional discoveries, which I could have reserved for myself [by not rushing into print]. But all of us (especially myself) are creatures of a day. I am truly anxious that these discoveries should be made public as soon as possible for the glory of God, who desires to be known from

the book of Nature. The more is constructed from it by others, the more shall I rejoice. I shall envy nobody. This was my vow to God;

this is my resolve. I wanted to be a theologian. For a long time I was

troubled. Behold, God is glorified by my work in astronomy too. . . . Had I ever wished to be a professional astronomer even in this work,

had I not undertaken

should be less astonished

11. lbid., XIII, No. 23:251-60.

the entire task for the sake of pleasure, I

[by my discoveries .!!

Bibliography

Arnoldt, Daniel Heinrich. Ausführliche und mit Urkunden

versehene His-

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Baumgardt, Carola.

Johannes Kepler: Life and Letters. With an introduction

by Albert Einstein. New York: Philosophical Library, 1951.

Berger-Levrault, Oscar. Annales des professeurs des academies et universites alsaciennes 1523-1871. Nancy, 1892. Brahe, Tycho. Tychonis Brahe dani opera omnia, ed. J. L. E. Dreyer. Copenhagen, 1913-29. Burke-Gaffney, Michael Walter, S.J. Kepler and the Jesuits. Milwaukee: Bruce Publishing Company, 1944. Caspar, Max. Bibliograpbia Kepleriana. Munich, 1936. . Johannes Kepler. 3d ed. Stuttgart: Kohlhammer, 1958. . Kepler, tr. and ed. C. Doris Hellman. London and New York: Abelard-Schuman, 1959. Caspar, Max, and Walther von Dyck (eds.). Johannes Kepler in seinen Briefen. 2 vols. Munich and Berlin, 1930. Dijksterhuis, Eduard Jan. The Mechanization of the World Picture, tr. C. Dikshoorn. Oxford: Clarendon Press, 1961.

Drake, Stillman. Discoveries and Opinions of Galileo. Garden City, LL:

Doubleday, 1957. Dreyer, John Louis Emil. Tycho Brahe. Edinburgh, 1890; reissued, New York: Dover Publications, 1963. Frisch, Christian (ed.). Joannis Kepleri astronomi opera onmia. See Kepler, Johannes. Galilei, Galileo. Le Opere di Galileo Galilei. National edition. Florence, 1890-1909; reprinted, 1929-39. Great Books of tbe Western World, Vol. 16. Chicago: Encyclopaedia Britannica, 1952. Günther, Ludwig. Ich greife Gott mit Handen, ed. Johannes Günther. 3d ed. East Berlin: Evangelische Verlagsanstalt, 1960. (tr. and ed.). Keplers Traum vom Mond. Leipzig, 1898. Partially reprinted in Physikalische Blatter, 1958, 14:433-41.

Günther, Siegmund. “Johannes Kepler und der tellurisch-kosmische Mag-

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Knight,

David

C. Johannes

Kepler

and Planetary

Motion.

New

York:

Watts, 1962. Die Matrikel der Universität Königsberg in Preussen, ed. Georg Erler. Leipzig, 1908-17. Koestler, Arthur. “Kepler and the Psychology of Discovery,” pp. 49-57 in

The Logic of Personal Knowledge, Essays Presented to Michael Polanyi.

London: Routledge & Kegan Paul, 1961; Glencoe, Ill.: Free Press, 1961. . The Sleepwalkers. London: Hutchinson, 1959; New York: Macmillan, 1959. . The Watershed. Garden City, L.I.: Doubleday, 1960; London: Heinemann, 1961. Lear, John (ed.). Kepler’s Dream. Tr. Patricia Frueh Kirkwood. Berkeley

and Los Angeles: University of California Press, 1965.

Lingelsheim, G. M. Briefe G. M. Lingelsheims, M. Berneggers und ihrer Freunde, ed. Alexander Reifferscheid. (Quellen zur Geschichte des geistigen Lebens in Deutschland wahrend des siebzehnten Jahrhunderts, Vol. I) Heilbronn, 1889. List, Martha. “Der handschriftliche Nachlass der Astronomen Johannes Kepler und Tycho Brahe" (Deutsche geodatische Kommission bei der

Bayerischen Akademie der Wissenschaften, Reihe E, Geschichte und Ent-

wicklung der Geodäsie, 2) 1961. Müller, Adolph, S.J. Johann Keppler, der Gesetzgeber der neueren Astronomie. (Stimmen aus Maria-Laach, Ergänzungsheft 83) Freiburg im Breisau, 1903. Nicolson. Marjorie Hope. "Cosmic Voyages," ELH, 1940, 7:83-107. . “Kepler, the Somnium and John Donne,” Journal of the History of Ideas, 1940, 1:259-80. Reprinted in Roots of Scientific Thought, eds. Philip P. Weiner and Aaron Noland. New York: Basic Books, 1957. Pp. 306-27. . Science and Imagination. Ithaca: Cornell University Press, 1956. . Voyages to the Moon. New York: Macmillan, 1948; paperback reprint, 1960. . 4 World in tbe Moon. (Smith College Studies in Modern Languages, Vol. 17, No. 2) Northampton, Massachusetts, 1935-36. Oppolzer, Theodor. Canon of Eclipses, tr. Owen Gingerich. New York: Dover Publications, 1962. Otto, Gottlieb Friedrich. Lexikon der . . . oberlausizischen Schriftsteller und Künstler. Görlitz and Leipzig, 1800-1821. Reitlinger, Edmund. "Kepler's Traum vom Monde," Sirius, 1871, 4:113-17, 121-25, 129-32, 137-44. Rosen, Edward (tr. and ed.). Kepler's Conversation with Galileo’s Sidereal Messenger. New York and London: Johnson, 1965. Schickard, W. Epistolae W. Scbickarti et M. Berneggeri mutuae. Strasbourg, 1673.

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Johann Siebmacher’s grosses und allgemeines Wappenbuch. Revised ed. (Der Adel Oberösterreichs, eds. Alois von Starkenfels and Kirnbauer von Erzstatt) Nuremberg, 1885-1904.

Stelling-Michaud,

Sven

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Le

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de L'Académie

de

Genéve 1559-1878. (Travaux d'bumanisme et renaissance, Vol. 33) Geneva: Droz, 1959. Stockl, Karl (ed.). Kepler-Festschrift. (Bericht des naturwissenschaftlichen Vereins zu Regensburg, Vol. 19) Regensburg, 1928-30. Die alten Matrikeln der Universitat Strassburg 1621 bis 1793. (Urkunden und Akten der Stadt Strassburg, 3d Abt., ed. Gustav C. Knod) Strassburg, 1897-1902. Die Matrikeln der Universitat Tubingen, eds. Heinrich Hermelink, Albert Bürk, and Wilhelm Wille. Stuttgart and Tübingen, 1906-54. Album academiae Vitebergensis. 3 vols. Leipzig, Halle, and Magdeburg, 1841—1952. Walther, P. A. F. “Landgraf

Philipp

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| genannt ‘der Dritte,’

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Index

Aberration, chromatic, 77 Acosta, José de, 1327, 135 Aelianus, Claudius, 2147 Affo, Ireneo, 1507

Athens, 214 Atlantis, 30 Augsburg, 180, 181, 182 Augsburg Confession, 36 Augustine, Saint, 517 Aulis, 65 Austria, 189

Africa, 21, 30

Agricola, George, 1577

Air: height of, 637, 907; need for, 64 Algarotti, Vittorio, 205

Austrian

American Numismatic Society, 1277

National

Library,

Anstruther, Robert, 199

1847 Autopsy, 203, 205 Averroes, 677, 687 Avicenna, 1567 Azores, 31

Aphelian distance, 917

Bachaczek, Martin, 35

Anian Strait, 114

Antipodes, 25 Antonini, Alfonso, 1007 Aperture, 75, 1167, 137, 141, 142 Apian, Philip, 987

Apogee, 88 Apollonius, 1267 Arber, Edward, 2127, 2137 Arcetri, 235

Arctic Circle, 45, 487, 85, 115 Aristarchus, 907

Aristotle:

death, 42, 214-15; his classi-

fication of the moon, 66, 67n; On tbe Heavens, 67, 218n; translated by

Kepler, 672; Generation

of Animals,

682, 146n; Meteorology, 73n, his concept of gravity, 218, 222 Aristotle, Pseudo-: Mechanics, 11122; On Colors, 1107, 111 Arithmetic, 957

1567; 106,

Arnobius the African, 132, 1337 Arnobius the Younger, 1327

Arnold, Matthew, 427 Arnoldt, Daniel Heinrich, 2007, 241

Astrolabe, 177 Astrology: Kepler' attitude toward, 471, 51, 54, 567, son; doctrines of, san, 55”; Bartsch’s addiction to, 178, 185

Astronomical unit, 917 Athenae Rauricae, 195n

6172,

1337,

Barabashov, N. P., 1297 Barnacle goose, 1347 Bartholin, Erasmus, 457 Bartholin, Thomas, 203, 204, 205, 206 Bartsch, Frederick, 179, 183, 190 Bartsch, Jacob: printed Kepler’s Dream, xxi-xxll, XX11172, 6, 1497, 210; correspondence with Kepler, 116, 179, 181,

182;

education,

177,

178,

179,

180;

publications of, 177, 178, 179, 180, 181, 183, 196; married Susanna Kepler, 183-90; correspondence with Bernegger, 1957, 196 Bartsch, Susanna, née Kepler, xxiiz, 183—90, 192, 193, 201 Dasel, 195, 197, 241 Bayle, Pierre, 67 Beckher, Daniel, 200, 2047, 205 Belgian: used interchangeably with “Dutch,” 1257, 1267 Berger-Levrault, Oscar, 1907, 191, 192, 193, 241 Bernegger, Johann Kaspar, 188 Bernegger, Matthias: correspondence with Johannes Kepler, xix, xx, 1167, 1667,

245

185,

186,

187,

188,

ceived Kepler's portrait,

189,

190;

1777,

re-

1857;

246

Index

Bernegger, Matthias (continued) correspondence with Bartsch, 186-87, 188, 196; correspondence with Schick-

ard,

Kepler,

195;

195,

relations 196,

197,

with

Galileo’s Dialogue, 198 Berthold, Gerhard, 231

Ludwig

198; translated

Besold, Christopher, 32, 55, 207 Bessard, Toussaint de, 1007 Bidez, Joseph, 427

Bieler, Ludwig, 347

Boehmer, George

Boisacq, Emile, 787 Bolton, Herbert E., 224”

Boon, George van der, 234 Brahe,

Tycho:

astronomical

observa-

tions of, 77, 82, 13, 56, 58, 917%, 1007, 1217, 181, 213, 228; pupils of, 12, 13, 46n, 607, 62m, 216; on Iceland, 35, 43, 44, 49; death, 397, 213; correspondence of, 44, 1377, 1387; relations with Kepler, 447, 467, 48n, 6on; Description of His Instruments, 457, 47n; established observatory, 457, 216; “Treasury of Observations,” 567, 1387, 226; as Imperial Mathematician, 1207, 1387; on moon’s diameter, 138; Prolegomena, 138n; Preliminary Exercises, 1397, 227; on comets, 1502; Meteorological Observations,

216; Astronomical Letters, 227

Breitschwert, J. L. C., xxi

Brendan the Navigator, 34

Bry, Theodore de, 1717 Bryk, Otto J., 193 Buchanan, George, 307, 43, 467 Burckhardt, Albrecht, 1957 Butzbach, 57, 77, 1167, 184

Caecius, Mt., 127

193,

2307,

Emperor,

Charles University, 35

H., 417

Bohemia, 11, 1497, 156, 227

Botany, 43 Bothnia, 44

Caspar, Max, 97, 377, 417, 241 Catania, 1317 Caxton, William, 347 Cesi, Federico, 235 Chacon, Alfonso, 166n Chalcis, 214 Chantraine, Pierre, 507 Charles IV, Holy Roman 357

Caesar, Julius, 307 Calendar: Gregorian, 567, 1387; Julian, son, 1387 Callippus, 1077 Cardan, Jerome, 1317 Carter, Charles Howard, 607

Cherniss, Harold, 317 Chiaramonti, Scipione, 1507 Chile, 132, 1712 China, 357, 171 Christina Sophia, marchioness of East Friesland, 87 Chroust, Anton-Hermann, 2157 Cicero, 30 Clark, Joseph T., 2347 Cleombrotus, 165 Clissold, Stephen, 2247 Clouds, 146, 147 Clouston, Joseph S., 467 Cola (Sicilian man-fish): legend of, 130, 13172 Color: Kepler's theory of, 72, 109, 110, III

Colpo, Mario, 2347

Colure, 85. See also Solstitial colure Comet, 1507, 229, 2337 Compass, 1012, 151 Conjunction, 1237, 1397, 144, 1607 Copenhagen, 13, 204, 206, 216 Copernicanism: attitudes toward,

xvii,

367, 377, 642, 1007, 1427, 198

Copernicus,

Nicholas:

Revolutions,

387, 397, 235; in Donne’s

Conclave,

39; attitude toward Averroes, 687; his “great circle,” 877; used by Kepler, 917; his concept of gravity, 218; his classification of the earth, 219 Copula, 1237 Coronado, Francisco, 224 Cosmas of Prague, 117 Counter-Reformation, Catholic, xxi, 487, 1497, 178, 186 Criger, Peter, 367, 199, 205

Cysat, Johann B., 231, 2357

247

Index Daemon: as divinity, 15, 50”; derivation of, 50, 51”, 627; as fire-dweller, 687

Danzig, 199

Day:

natural, 20, 52, 897,

107; artificial,

527; start of, 104, 166. See also Equinoctial day

Declination: magnetic, xvii, 22, 98, 9972, 1007, 1017; lunar, 487 Degree, 897 Denmark, 45, 49, 227 Diaphragm, 1457 Dibner, Bern, 387

Dice, 51, 527

Dieterich, Johann, 194 Digit, 1437, 144 Dignity, astrological, 54, 55 Diogenes Laertius, 337, 41,

215

Disputation, academic, xvii, 135, 141%, 1437, 208 Divisor, 17, 797, 80, 93 Donne, John, 387, 397, 212-13

427,

gon,

557,

647,

Dounot, Didier, 1007 Drachmann, Aage G., 1067

Drake, Stillman, 537, 1987, 241

Dreyer, J. L. E., 352, 46n, 56”, 6on, 241 Duecaledonian Ocean, 114

Duhr, Bernhard, 2347

Düring, Ingemar, 2147 Durlach, 184, 185, 190 Durocotti, 307

Dutch: used interchangeably with "Bel-

gian," 125 Dyck, Walther von, 241 Dyson, Frank, 767

motion

Ebner, Eduard, 317 Eclipse: attitude toward,

of the earth, 25, 117, 118, of, 26, 1227; frequency of —, lunar, 15, 25, 617, 637, 143; duration of, 66, 70, of, 767, 117; redness in,

1623,

Douglas, George, 199

Earth:

792, 116; distance from moon, 8;, 902; distance from sun, 85, 907, 91; as a luminous body, 103; position in universe, 218 Easter, 827 East Friesland, 87, 2287, 229 East Prussia, 204

of, xvil, 397, 55”, 647,

677, 82, 105, 106; shadow of, 16, 63, 66, 1217, 122; apparent motionlessness

of, 17; called Volva by Kepler, 17, 78; rotation of, 247, 327, 787, 79, 105,

106, 107, 114, 119; as a planet, 517, 218, 219; radius, 62, 127%; as a living animal, 707; as a magnet, 73, 747; similarity to moon, 747, 171, 218; as cause of lunar eclipse, 767; annual revolution of, 797, 85, 86, 105; axis,

136%;

of

1590,

17, 63, 1307;

119; middle total, 76 76, 98, 120, 120; cause 121, 147; of

1437;

of

1605,

146, 1477 —, solar, 17, 25, 26, 637, 118, 142, 1437 cause of, 25, 63, 76”, 117; Of 1605, 58, 142; of 1567, 627; of 1612, 126, 1272; of 1598, 1377, 1387; effect on moon's apparent diameter, 138, 141 Ecliptic, 58, 79, 84 Egypt, 165, 171 Ehem, Philip, 183, 184 Ehem, Regina, née Lorentz, 183 Einarsson, Guömundur, 417

Einarsson, Oddur, 437, 216-17

Eisenschmidt, Johann Caspar, Elbe River, 156 Elements, four, 68n Elie, Hubert, 210

Elliptic orbit, 947 Empedocles, 41, 427

191

Enns River, 127 Ephemerides, 181 Epidemic, 1957, 202, 203, 204, 205 Equator: lunar, 17”, 18, 84; terrestrial, 18; celestial, 58, 83 Equinoctial day, 557, 81, 82, 84 Equinoctial point, 58, 847 Equinox, 19, 55%, 81, 847 Eratosthenes, 1267 Ernout, Alfred, 787 Erosion, 156, 1577 Eskimos, 467 Ether, 15, 637, 71 Ethics, 50 Etna, Mt., 41, 427, 487, 167 Euclid, 1007

248

Index

Euripus, 42,

214

Exaltation, astrological, 55 Fabricius, David: correspondence with Kepler, 597, 617, 74n, 110M, 132m, 14772, 221, 225, 227-30; astronomical observations of, 1387, 226-29, 232; astronomical ideas of, 140, 145; Prognostications, 1402, 231; as theologian, 238 Fabricius, Johannes, 230-32, 2357 Ferdinand II, Holy Roman Emperor, 1497, 1667 Fernel, Jean, 179 Finland, 44 Finns, 52 First motion, 19, 3271, 79 First movable sphere, 115 Florence, 407 Focus, 1237 Foot, Roman, 77 Fowler, John, 1997 Frankfurt book fair, 181, 182, 190, 231 Frankfurt/Main, xxii, xxiil, 6, 9, 28, 347,

190

Frederick V, king of Bohemia, 178 Frederick Achilles, duke of Württemberg, 497

Friesland, 227. See also East Friesland

Fringe, 118, 141 Frisch, Christian, 277, 193, 241 Frisk, Hjalmar, 507 Frost, 20, 89

9572,

1367,

168m,

correspondence

with

Gaedertz, Karl Theodor, 347 Galen, 196

Galilei,

Galileo:

Pieroni, xxii, xxiii, 201; Sidereal Message, $3, 1097, 112, 1267, 128; correspondence with Johannes Kepler,

$571, 10972, 12571, 13571, 1632; Dialogue,

692, 198; correspondence with Antonini, 1007; Sumspots, 105872; on water in the moon, 1097; astronomical observations of, 125, 151; Assayer, 126, 1287; his telescopes, 129, 1677; given information about Zucchi, 1507; cor-

respondence with Ludwig 201; imprisonment, 231, 235

Kepler,

Gassend, Pierre, 2067 Geneva, 197 George II, Landgrave of Hesse-Darmstadt, 87 Gilbert, William, xviii, 987, 99, 1007, 10172 Gingerich, Owen, 927, 242 Globe, celestial, 179, 180, 226 Goppingen, 647 Görlitz, 1162 Grassi, Orazio, 1267 Gravitational attraction, 747, 219-21 Gravity, 71, 123, 1597, 218-21 Graz, 33, 4872, 1387, 233, 237, 238 “Great circle,” 87 Greenland, 31, 45, 1347 Gregory XV, Pope, 1667 Gregory of Nazianzus, 214 Grimstone, Edward, 1327 Guadalquivir River, 224 Guagnini, Alessandro, 237 Guldin, Paul, 149, 1507, 1667, 1687, 23335 Gunpowder, 159 Günther, Johannes, 241

Günther,

Ludwig,

92, 412,

537,

241 Günther, Siegmund, 9872, 99n, 241

1377,

Hafenreffer, Matthias, 1427, 1477

Hafenreffer, Samuel, 6472, 1417 Hall, A. Rupert, 1597 Halldórsson, Jon, 217 Haller, Albrecht von, 205 Hamburg, 192 Hammer, Franz, 337, 1367, 1397, 1847 Hammerich, Frederick, 204 Hansch, Michael G., 1337, 1957, 206, 241 Hansen, Joseph, 657 Hauptfleisch, Christoph. See Sarcephalus, Christopher Heath, Thomas L., 9o7 Hebrew, 53, 57, 78 Heidelberg, 211 Hekla, Mt., 12, 34, 39, 41, 487 Herberstein, Sigmund, 237, 238

Herberstein, Sigmund Frederick, 237 Hermannson, Halldór, 357, 457 Herodotus,

1617, 165

Index Herrera, Antonio de, 1717 Herwart

von

Hohenburg,

chancellor

of Bavaria, 157, 517, 597, 99n, 1177, 1347, 137 Hesse, Landgrave of (William IV), 44

Hevelius, Johannes, 205 Heyden, Jacob von, 1777

Hignett, Charles, 1617

467, 547, 66n, 69n, 122%, 129n, 17471, 209-11; marriages, Xxii2, xxlli7, 1897, 2087; personality, 157, 737, 757, 8371, 1147; poor eyesight of, 3572, 229; re-

Hohenfelder, Marcus von, 1437, 207 Holar, 437

fused to become a Catholic, 487, 235;

Holborn, Hajo, 607 Holderlin, Friedrich, 427 Holtzmann, Wilheln, 211 Holy Roman Empire, xviii, 196, 237 Homer, 42, 215 Horoscope, 597

attitude toward astrology, 547; attitude toward witchcraft, 65”; translated Aristotle, 677; teleological viewpoint of, 787; his knowledge of French, 997; as a German nationalist, 162”; relations with Bartsch, 179-83, 185-91; his unpublished manuscripts,

Horst, Gregor, 184 House, astrological, 54

Hungary, 194, 202, 206 Hven, 12, 447, 457, 567

201, 206

Ibn Rushd. See Averroes Ibn Sina. See Avicenna Iceland: other names for,

11, 357,

as scene of Kepler’s Dream, language, 357, 45; location, 115; history, 45; people, 49

115;

30, 35;

43,

49,

Index of Prohibited Books, 497

Indo-European, 787 Inertia, 167, 73, 222-23 Infinity of universe, 777 Inn River, 127 Inquisition, Holy, 198, 235 Irradiation, 1397

Frederick,

duke

Justin Martyr, 214 Kansas, 224 Kastner, Abraham

G., 77

Planet Mars. See Kepler's New

tronomy —Conversation

with

the Sidereal

As-

Mes-

169; cited, 1092, 1107, 112, 125, 128, 135, 136, 140, 1637 —Cosmographic Mystery: 2d ed., 16m, 1507; 1st ed., 377, 487, 647, 917, 1427, 207, 237, 239 —Discourse on the Great Conjunction, $971, 1367 —Ephemerides: publication of, xx, 817, 102, 182; quoted, 817, 1027, 136m, 1407, 1467, 230; diagrams in, 119;

Jochner, Georg M., 597

berg, 49

Works —Admonition to Astronomers, 7n, 16771, 178, 190 —Answer to Roslin, 230 — Calendar for the Year... 1599, 13872 —Commentaries on the Motions of the

senger: title, 537; quoted, 557, 109”,

James I, king of England, 577 Jammer, Max, 697, 7on

Julius

Keller, Jacob, 234 Kepler, Johannes: as a student at Tiibingen, xvii, XX, 537, 787, 207; his lunar dissertation, xvii, xx, 327, 417, 542, 5571, 99722, 1207, 1287, 129n, 1307, 207-8; as Imperial Mathematician, Xvili, 3772, 607%, 927%, 1307, 207; his

translation of Plutarch, xxi, 317, 347,

Hipparchus, 637 Hippocrates, 183

Jónsson, Finnur, 216 Jostel, Melchior, 61” Julian the Apostate, 215 Julich-Cleves, 597

249

parts

of

Württem-

of,

140,

145,

177,

182,

230;

Bartsch's collaboration in, 182 —Epitome of Copernican Astronomy: cited, 167, 55, 62, 667, 67, 827, 897, 947, 967, 1037, 118, 120, 124, 125, 1367, 1672; publication of, 567, 997;

quoted, 637, 677, 737, 77”, 84n, 877,

8872,

907,

947,

987,

997,

1007,

1077,

Index

250

Kepler, Johannes: Works (continued) 11372, 119%, 1207, 125M, 127”, 166m, 222; definitions in, 797, 807, 817, 837, 847, 897, 1177, 12171, 122M, 1237, 1357); diagram in, 102 —Forecast for the Year 1605, 59n

—Harmonics:

quoted, 577, 70”; cited,

QIN, 9371, 1317, 1507, 184 —Hipparchus, 62, 63, 1177, 205

—Letter about the Solar Eclipse, 58n, 5972, 997

—New Astronomy or Commentaries on ... Mars: Introduction, 377, 697, 74M, 219, 220; quoted, 617, 747, 1017, 1287, 222, 223, 229; errors in, 9275 cited, 9472, 128, 1317, 230; title page, 238 —New Star, 77N, 9on, 1327, 136, 160, 212, 228, 230

—Optics:

cited, xxi, 34, 55, 57, 110, III,

112, 13672; quotes Plutarch, 34, 1087,

1257, 171, 209, 211; publication of, 347, 141, 227; quotes Mastlin, 557, 1437; observations in, 57, 61”, 767;

calculations in, 627; quoted, 727, 737, 11072, 11172, 1127, I217, 1297, 1397,

1402, 1437, 1447, 1597, 227; instruments in, 75, 76n; praises Gilbert, 1007; experiments in, 109, 1377, 143; introduces new terms, 1172, 1237; diagrams in, 120, 137%; discusses Cardan, 1317; errors in, 227, 228, 230 —Reply to Jacob Bartscb's Letter, xx, 116,

181

—Report

on His Observations of Jupi-

ter’s Four

Satellites,

163,

164n,

165,

1677, 1697 —Rudolphine Tables: cited, 56n, 197; printing of, 927, 1207, 180, 181, 184; precepts of, 1447; quoted, 180, 2387 —Shieldbearer for Tycho, 126, 1507, 162, 1677 —Singular Phenomenon, 35n, 61n, 141n —Supplement to the Thousand Logarithms, 8n, 95n

—Tertius interveniens, 236

—Thousand Logarithms, 8n, 95n Kepler, Katharine, 367 Kepler, Ludwig: dedicated and published Johannes Kepler's Dream, xxii-

xxli, 5-9, 194, 198; birth, 587, son, 194; attended Bartsch’s wedding, 190; medical activities, 194-97, 200-206; obituary, 19571, 197, 200 Kepler, Margaret, 327, 40n Kepler, Susanna. See Bartsch, Susanna Kestner, Christian Wilhelm, 204

Klug, Josef, 232

Kneiphof, 200 Königsberg, 1957, 200, 202-6, 242 Kranz, Walther, 427 Kreczi, Hanns, 2337 Kroess, Alois, 1667, 234 Labrador, 31 Lameere, William, 687

Lapland, 44

Lapps, 52 Latitude, 22, 437, 987, 99n Lauban. See Luban Lawson, John, 1267 Lazius, Wolfgang, 1277 Lebanon, 787 Leiden, 1257, 204 Leipzig, xxi, 40, 178, 181 Leningrad, 193 Levania (Kepler's term for the moon), 14-19, 25-27, $071, 53 Libussa, ruler of Bohemia, ıı Light: Kepler's theory of, 727, 159; communicated, 1117, 112; speed of, ı60n Limits, 58, 84

Linz: Johannes Kepler in, xix, 87, 367,

4071, 627, 122, 134, 1667, 184, 209, 233; 62; Ludwig Kepler in, 233 Lipsky, Yu. N., 1297 List, Martha, 1937, 20671, 242 Logarithm, 87, 95, 191

Longberg,

138, 1407

Christen

13672, 1497, 1507, polar altitude at, in, 196; Landhaus

1967,

197^,

201”,

S., 437, 46n, 617,

Longitude, 22, 4371, 98, 997 Longomontanus. See Longberg,

Chris-

ten S. López de Gómara, Francisco, 2257 Loth, Georg, 200 Luban, xxi, xxii, 177, 178, 181, 183, 201

189.

Index Lübeck, 204, 205, 206

Lucas, Frederic William, 467 Lucian, 32, 337, 347, san Lucumoria, 133, 236 Lunation, 83 Lusatia, xxiii, 6, 180, 182, Lutheran church, 367, 467

185,

186,

191

251 85, 907; rotation of, denied by Kepler, 23, 78, 797; density, 27, 747, 1287; shape, 27, 83, 153; mountains on, 27, 125, 1267, 127, 170, 171; nodes, 58, 84, 102; shadow of, 63; true motion of, 66; kinship with earth, 66, 67”,

697, 747, 1257, 171, 218; parallax of,

McCracken, George E., 1327

66, 94; apparent radius, 66, 94; as a cause of tides, 69-70; as a magnet, 73; phases of, 767, 81, 86, 92, 1137, 121,

Magdaleneum, 177

109,

Macrobius, 677 Maelcote, Odo van, 1057

1387,

Magellan's region, 108, 115 Magnet, 1017 Magnus, Olaus, 487, 52 Marius, Simon. See Mayr, Simon Mars: distance from sun, 91 Marwick, Hugh, 467 Mass, 697 Mastlin, Michael: edited Kepler's Cosmographic Mystery, 37n; correspond-

ence with Kepler, 3772, 447, 547, 1387, 1392, 207, 239; as Kepler's teacher, 37”, 64, 125, 207; his disputation on

eclipses,

5572,

1437;

attitude

toward

Copernicanism, 647, 1427, 207; attitude toward Averroes, 687; as pupil

of Apian, 997; his disputation on the planets, 135, 1417; correspondence with Brahe, 1377, 1387; as friend of Kepler, 1477; attitude toward Johannes Fabricius, 231

Matthias, archduke of Austria, Mayr, Simon, 232

11, 1307

Medicine, 43, 447, 50, 178, 194 Meissen, 156

Mercator, Gerhard, 467, 225 Meridian, 457, 83

Metaphysics, 50

Metzner, Erwin, 367 Meurs, Johannes van, 1267 Migne, Jacques Paul, 1667, 2157 Mikhailov, A. A., 1297 Mile, German, 15, 27, 62, 125, 127, 170 Mira Ceti (variable star), 227, 228, 230

Mogling, Daniel, 184

Moldenhauer, Jacob, 2037 Month: natural, 23, 80, 96, 102; synodic, 837, 1027; sidereal, 837

Moon:

distance from earth, 15, 65, 777,

14372, 112%,

144; spots, 77, 80, 113%,

151,

158,

96,

1627;

106,

names

for, in other languages, 78; revolution of, 78, 80, 84, 86, 93, 96; rotation of, 787; axis, 79, 80, 84, 93, 96; circle of illumination, 81; orbit, 84, 91, 94; poles, 84, 94, 96; motion in latitude, 85, 93, 102; size, 124; diameter, 127,

170; motion away from sun, 1367; first visibility of, 1367; limb of, 145, 146. See also Levania

Moonlight: warmth of, 12: Moravia, Xxili72, 2027 Mountains: creation of, 156

Müller, Barbara, xxii?, 194

Müller, Philip, xx, xxi, 178, 189, 192 Müller, Veit, xvii, 32, 207, 208 Mur River, 109, 1107 Mylius, Arnold, 1277

179,

181,

Naples, 407 Narcotics, 16 Nautonier, Guillaume de, 997 Nero, 161, 165 Neugebauer, Otto, 927 Newton, Isaac, 219 Nifo, Agostino, 687 Night, 80, 827, 107 Nodes: lunar, 58, 84, 102; orbital, 847 Nonnus, 215 North America, 115, 225 Norway, 11”, 12, 457 Nova, 11%, 357, $97, 1607, 212, 213, 227, 229

Novaya Zemlya, 35 Number:

triangular,

logistic, 957

Nuremberg, 62

51;

absolute,

957;

Index

252 Occultation,

Odenberg, Odlozilik, Olympus, O'Malley,

102, 144

2027 Otakar, 357 Mt. (in Asia), 73 Charles D., 1267

O'Meara, John J., 51” Oppolzer, Theodor, 587, 617, 62n, 76n, 12072, 1267, 1367, 1377, 138m, 1437,

14771, 242

Opposition, 1237, 1397 Orkney, 43, 44, 45, 467 Orsini, Alessandro, 1507, 1667 Ortelius, Abraham, 467, 1277, 225 Otto, Gottlieb Friedrich, 1917, 193, 242

Porphyry, 51

Pachollen, 199, 2007

Pacific Ocean, 11427, 224

Padua, 179, 180, 200, 201, 206 Panama, 1147 Parabola, 159n Passau, 202

Patrick, Saint, 34

Penumbra, 117 Perihelian distance, 91” Peripatetics, 152 Peru, 1357, 171 Peurbach, George, 33 Philip III, Landgrave of Hesse-Butzbach, 5,72, 87, 116, 184

Philip Ludwig,

burg, 587

Count Palatine of Neu-

Picard, Jean, 457 Pieroni, Giovanni, xxii, xxiii, 201, 235 Pisani, Ottavio, 1507

Pitré, Giuseppe, 1317

Planets: number of, 517; cause of motion of, 707, 219, 220, 238; as movable bodies, 767; as material bodies, 222,

223; Orbits of, 229

Plato, 30, 507

by

Kepler,

xxi, 317,

1087; misinterpreted

by Kep-

692, 1292, 211; read by Kepler, 31, 33, 54, 66, 75, 129; quoted by Kepler,

33-34.

62;

Snel

in,

1267;

Cardinal

Orsini

166n; Susanna Kepler in, 183; wig Kepler in, 194 Prickard, Arthur Octavius, 2327 Privolva, 17, 21, 79 Procopius of Caesarea, 215

in,

Lud-

Projectile: trajectory of, 159

Prussia, 199, 202, 206 Prussian Tables. See Reinhold, Erasmus Ptolemy: Geography, 30n, 114n; Har-

monics,

51n;

Tetrabiblos,

san,

557;

compared with Copernicus, 647; his ratio of the orbits, 86, 877; Syntaxis, 8772

Public Record Office, 199 Pupil of the eye, 145 Pyramid, 170

Plutarch: translated by Kepler, xxi, 317, 347, 547, 667, 1227, 129", 1747, 209-

annotated

Porta, G. B. della, 1347 Prague: Johannes Kepler in, xvin, xx, 33, 347%, 57, 627, 75, III, 1267, 212; capital of Holy Roman Empire, xviii, 4072, 587, 59n, 99n; University, 357; Kepler’s Dream taken from, 40, 557, 212; Brahe in, 60”; polar altitude at,

Purgatory, 34, 487

Pliny the Elder, 42, 1337, 1617 Pliny the Younger, 427 11;

ler, 467; contradicted by Kepler, 1082; accepted by Kepler, 1257, 1407, 171 Plutarch, Pseudo-, 427 Poles: lunar, 17, 21, 23, 96, 97; celestial, of the earth, 17, 22, 79, 807, 81, 85, 97, 98, 115; terrestrial, 22, 24, 44, 82, 100, 1017; altitude of, 22, 62; celestial, of the moon, 22, 797, 80, 81, 83, 84, 94, 97, 104; Of the ecliptic, 22, 80, 81, 94, 97, 104, 116; of a great circle, 97; magnetic, 987, 10171 Pollentz, Frederick von, 200 Polo, Marco, 1147 Pompeii, 42 Popayan, 115

Pythagoras, 38, 907 Pythagoreans, 377

Quadrature, 81 Quincunx, 160 Quivira, 21, 224-25

Index Rain, 132, 147

253

Rudder, 44 Rudolph II, Holy Roman Emperor, 9271, 12072, 13071, 13871, 1677

Rass, Andreas, 597 Rauschmayr, J. S., 5972

Ray, visual, 121 Reformation, 185

Russia, 236, 237

Regensburg, 184, 196, 197, 201 Reifferscheid, Alexander, 1877,

188m,

192, 242

Sabra, Nancy, 199

Sagan. See Zagan Sahm, Wilhelm, 2047

Reindeer, 44 Reinhold, Erasmus: his edition of Peurbach, 33; Prussian Tables, 226 Reitlinger, Edmund, 487, 537, 242

Salusbury, Thomas, 377 Salzmann, Johann Rudolph, 179

Retrograde motion, 84 Reuttinger, Susanna, xxiiiz

Satellite, 1637 Sattler, Christian F., 497

Retina, 145

Rheticus, George Joachim, 377 Rhodius, Ambrosius, 617

Rio, Martin 236-38

Antony

del, 47, 52, 133,

Rollenhagen, Gabriel, 34 Rollenhagen, George, 34 Rome, 62 Rómer, Olaus, 457

Ronchi, Vasco, 143%, 1457

Rordam, Holger, 216 Rose, Herbert J., 507 Rosen, Edward: tr. and ed. Kepler's Conversation, xvin, 357, s6n, 109m, 1102, 1137, 1257, 1285, 1357, 136m,

14172, 169”, 242; "Kepler and Witch-

craft Trials," 327, 65n; Three

nican

Kepler:

Treatises, Their

11,

38n;

Coper-

“Galileo

First Two

and

Contacts,”

532; "Keplers Rake Was Not a Hoe," 537; review of Rossmann, 671; "Copernicus Quotation from

Sophocles," 687; “The Moon's Orbit in Keplers Somnium, gan; The Naming of the Telescope, 135n, 150m; translation of Ronchi, 1437; “Thomas

Seget of Seton,” 1637; review of Caspar, 2037; “Kepler’s Harmonics and His Concept of Inertia,” 2237; review of Zinner, 2327

Rossetti, Lucia, 1807, 2017

Rossmann, Fritz, 677

Rostock, 62, 189 Rotation, 967 Royal Society of London, xviiiz, 206

Santillana, Giorgio de, 387 Sarcephalus, Christopher, 177

Scaliger, Joseph Justus, 337 Scaliger, Julius Caesar, 1317, 134 Scheiner, Christopher, 235 Schickard, Wilhelm, 77, 135727, 18072, 190, 192, 195, 242 Schiller, Julius, 180 Schmetzer, Adolf, 193 Schnurrer, Christian F., 5372, 1807 Schockel, Mt., 109, 1107, 1277 Schulze, Johann Daniel, 193 Sciametry, 6372 Scotland, 30, 43, 44, 1347 Screen, 757, 11672, 126 Scythia, 133 Sebisch, Melchior, 179, 183, 196 Second motions, 19 Seget, Thomas, 1637 Seiffart, Matthias, 60, 6172, 627 Semmering Pass, 1277 Shetlands, 117

Siberia, 225

Siebmacher, Johann, 67, 407, 1587, Silesia, xx, 156, 178, 181, 182, 183 Sinzendorf, August von, 197 Sinzendorf, Johann Joachim von,

197

Sloschek, Erich, xxiii? Snel, Willebrord, 125, 233 Socrates, 214 Solstice, 19, 437, 76, 85 Solstitial colure, 17, 807

Solstitial point, 847

Sopron, 202 Stahl, William H., 677, 127n

179,

243

67,

254

Index

Stars: fixed, 19, 77; variable, 226, 2297. See also Mira Ceti; Nova

Stefansson, Vilhjalmur, 467

ard

194

in,

179,

192;

Ludwig

Tycho. See Brahe, Tycho

Styria, 109, 1 1072, 201 Sun: apparent diameter, 267, 66, 90; parallax of, 66; rotation of, 787, 105; deemed motionless, 87; distance from earth, 907, 91; force emanating from, 219 Sunspots, 77, 105, 116, 230-32

Urban VIII, Pope, 1667

Surveyors, 77

Swabia, 39, 1447 Swiss Federal Astronomical tory, 1807

Observa-

Syzygy, 123

Tabarroni, Giorgio, 1097 Tacitus, 427 Tacking, 44 Talking machine, 607 Telemark, 117 Telescope: defects of, 77, 1667; earliest observations with, 537; reflecting,

1507

Terminator, 817, 126, 153

Traun River, 134 Trigonometry, 487, 98n Tropic, 85, 897, 132 Tropical point, 847 Troy, 65

Tübingen: Johannes Kepler in, xvii, xx, 3271, $371, 179, 207, 208; Besold in, 327;

attitude of University faculty toward

Copernicanism, 377, 1:427; Kepler's Dream taken to, 40; Samuel Hafenreffer in, 647, 1417; Mästlin in, 647,

1437;

Philip

Apian

Umbra, 117 Upper Austria, 57, 367, 196, 23372 Upsala, 497

Uraniborg, 457

Veer, Gerrit de, 357, 987, 1347

Venice, 467, 1627, 201 Vergil, 47, 487

Vespucci, Amerigo, 317

Vesuvius, 42 Vienna: capital of the Holy Roman Empire, 1497, 196; Guldin in, 1497, 233; Orsini in, 1667; Ludwig Kepler in, 196, 197, 201 Vision, 1407, 145 Voet, Daniel, 67 Vogel, Sigismund, 193 Volkersdorf, Baron von, 40 Volva (Kepler’s term for the earth), 17, 78 Vries, Gerard de, 67 Wackher 1677

von

Wackenfels,

xviii,

1477,

Wagner, Henry R., 1147 184

Wallenstein, duke of Friedland, 183

Thule, 11, 115 Tides, 68, 697, 123, 124, 219 Time: measure of, 897

1417,

Ulm, 180, 181, 182

Walderbach,

Thirty Years’ War, xxiii, 1497

in,

987;

Matthias Hafenreffer in, 1427; Schick-

in,

Turner, Paul, 327

Stephanus, Henricus, 209, 210 Strasbourg: Bartsch in, 6, 178, 179, 183, 185, 190, 191; Bernegger in, 185, 186, 192; Ludwig Kepler in, 1957, 196 Strassmayr, Eduard, 2337 Stupanus, Emanuel, 195

Stuttgart, 497

Kepler

Walther, P.A.F., 57, 77, 8n, 1847, Wandsbek, 227 Wattenberg, Diedrich, 2297 Wechel, Christian: heirs of, 210 Weidler, Johann Friedrich, 192, 193 Weigenmaier, Georg, 5372 Welser, Marcus, 1057 Weyermann, Hans, 1507 Wichita Indians, 224 Wieger, Friedrich, 1797 Wieringen, 1347

William IV, Landgrave of Hesse, 447 Wind, 44, 527

Wirmsberger, Ferdinand, 407

Witch, 327, 417, 477, 65 Witchcraft, xix, 367, 657

243

Index Witte, Henning, 1427, 1927, 193 Wittenberg, 617, 243

Wohlwill, Emil, 537 Wolfgang William, Count Neuburg, 587, son Wroclaw, 177, 178, 179 Württemberg, 49, 597, 194

Zagan: Dream printed in, xx, xxi; Kepler in, 116%, 1567, 182, 191

Palatine of

Xerxes, 161, 165 Xylander, Wilhelm, 209, 210, 211 Year:

sidereal,

84, 85

18, 84, 85; tropical,

255

19,

Zedler, Johann Heinrich, 1777 Zehentmair, Colmann, 357 Zenith, 83, 84

Zeno brothers, Antonio and Nicoló, 467 Zeschlin, Johann, 587 Ziegler, Johannes, 2027 Zinner, Ernst, 2317, 243 Zodiac, 19, 85; signs of, 55,94 Zone: lunar, 19; terrestrial, 19, 52; tropical, 9o, 132 Zucchi, Niccoló, 150, 166 Zürich, 657, 1807