Encyclopaedia Britannica [S2-US, 3 ed.]

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UNIVERSITY OF CALIFORNIA

AT LOS ANGELES

:

—

SUPPLEMENT TO THE

ENCYCLOPEDIA, OR

DICTIONARY OF

ARTS,

SCIENCES, AND

MISCELLANEOUS LITERATURE. IN

THREE VOLUMES.

Illustrated with Copperplates.

NON IGNORO QU^ BONA SINT, FIERI MELIORA POSSE DOCTRINA, ET QU.E NGN OPTIMA, ALIQUO MODO ACUI TAMEN, ET CORRIGI POSSE. CiCERO.

VOL. ELE

II.

PHI

^|)ilatjelpi)ia PRINTED Br BUDD AND B^RTR.iM,

FOR TIIOiMAS DOBSON, AT THE STONE HOUSE, N" 41, SOUTH SECOND STREET. 1803.

AE5

SUPPLEMENT TO

T.HE

ENCYCLOPAEDIA. L E

E Elfarome''^'-

T^ LECTROMETER,

—

A

cademy of for

Sciences at Paris, defcribed in the

Memoirs

1785.

Mr Coulomb had made fome experiments in examiDr Hooke's theory of fprings " ut tenjlo ftc

nation of vis ;"

gard

and found, that

it

was

furprifingly exad, in re-

force neceifary for twilling eladic wires. fufpended a nicely turned metal cylinder by a

to the

Having

and having given

fine wire in the direiftion of its axis, it

feveral turns,

and

left

it

to regain its natural pofilion,

revolution of untvv'illlng and twilling in times precifcly equal, whether ihefe oTcillations were of a few degrees, or confiiled of

heobferved, that

it

performed

all its

He thence concluded, that the force with which the wire endeavoured to regain its natural pofition was exactly proportional to its dillance from it. Engaged, foon after, by order from the Minifter of Marine, in an examination of the phen^ mcna feveral revolutions.

of the mariner's compals, he took this method of fufpcnding his needles, in order 10 obtain exafl me.ifures of the forces which caul'td them to deviate from the magnetic meridian. He made ibmc obfervations with needles I'o fulpendcd ; whicii are highly valuable to the When Iiis fuccefs philulbpher engaged in that liudy. in this relearch had fully gratilie J liis wifhes, he turned his thuughis 10 the exuinina'ion ot tlie law of electiic aiflion by the help of an ck Urometer liifpendcd in the

fame manntr.

ABDC

Plate

XXVII.

It is con(lru(5leJ as

(li^.

inclies in dianictjr

a

I.)

and

loUovs

repreiVnts a gl in heiglit.

ifs

This

:

cylinder, is

12

covered by on the un-

it by a prcjciSing fillet This cover is pierced with two round SuppL. Vol. II.

gl.ifs

plate fitted to

der lurlace.

L E

E

an inarument which meaI J lures the quantity of ele>5lricity in any eleiflrified The moll common elecflrometers are defcribed body. in the article Electricity (EncycL), n" 27, and 182 very valuable one is likewile defcribed in n° 233. 85. of the article Electricity in this Supplement; but there are ftill two eleftrometers, of which we have hitherto given no account, though they are of fuch value, that to pals them unnoticed would be unpardonThe firft, which is by much the moll accuable. rate and delicate inflrument of the kind that we have leen, was invented by Mr Coulomb, and is adapted to afcertain the fmalled quantity of redundant electricity. The fecond is a late invention of Mr Cuthbertfun, the ingenious improver of the air-pump, and is employed only to meafure the charge of large jars and batteries. Electrometer, by Mr Coulomb of the Royal Ais

holes of i|th inches in diameter. One of them Is in Elcar