The Principles of Meteorology

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iijjiiu

viinijii^v

iiifm"^^n^Tai I«v. TliQll^S TKOttER,

Aimcosiii!. K

vtm t

tltEBJiif

At fiw liitrme * be to as so exceedingly attenuated, and expanded,

common

orbit i)t S;-a hollow sphere, equal in circumference to tlie tn discussed seriously be to But this idea is too sublime turn.

fill

«uchan occasion as this, and I therefore return to the cons:,

ctic seas,

hem

the

!9i to

30

to]51bt'.

m

this

it

e altoges.

avoir-

rt

of the

11

ore ex-

that are

200

•ery

niperate e aj^cent

So that uator,

i^

one of

[

at the

1

?quence st in far

iVozen,

I

nioiin-

'

in

I

3

con-

rid iip-

mrre

ill

by the ranRC all timer', and the variations are indicated regions, extends tempeiate the in vvijich ; Uarometer of the the air is coneven to a number of inches. This shows, tliat than it is at place, siderably lighter at one time, in the same in its quanreduction a another ; which must be occasioned by that a circumstance, the Irom either and this may arise, tity acand place, one fiom withdrawn portion of it is temporarilv it ia decomposed, and part of a that or anotlier, cumulated in to it at another abstracted from tlie general mass, to be restored than without tme. The range of the Barometer is less within, in North also and for, the tropics, which is easilv accounted

'place at

;

the reason of America, than in the same latitudes in lAirope, winter, than in greater also It is which is perhaps unknown. that during fact, the to owing partly be in summer, which may northern our in air of amount greater a the former we liave the winter the air is In latter. the during than hemisphere, ran bed and exmore condensed in the xXorthern, and more

And leirg raised to a Southern hemisphere. the colthan warmer greater height abov? the earth, in the to the over tails natura!l> it der hemisphere, a proportion of in the have we which air of quantity lower side. This extra Sor.thern hcmthe to way same very the in winter, is restored hemduring the summer when the states of the two

panded

in the

isj^here,

;

reai-on, why we have ispheres are reversed.. This is partly the than in hummer; and it is so much heavier gales in winter, Barometer takes a wider also one of the reasons why the

range in that season of the year.

ndod to the top

11. Tlie

ilurope,

of the

i^ond

ed.

it

lan thd

part

iry

warmto 't

a

llir

Oligllt

M'CPting I

.;:!

in

the

same

m

air,

second point to be considered, if, the temperature the means by \\ hich it is equalis-

together with

discuss tlie does not belong to the Meteorolrgist, to nature and tlie merilsof the conflicting theories, respecting submaterial a is it origin of heat; or, to determine, whether orimatter, of particles stance, or only a vibration among tfie ground I shall this on and &c. ; percussion, ginating in friction, from Tlse heat of the atmosphere is either der ved not enter. his influence is but agency; his by motion in set is the sun, or be kept modified by a number of circumstances, which should not It does subject. in view, in all our calculations on this upon, effect sensible appear tliat the rays of the sun, have any with the earth, and arti tlie air, till they first come into contact It

'

12

METEOROLOGY.

reflected

by

its

surface

;

ibr the higher

we ascemi above the we at last attain to The more that air

earth, the colder does the air become, till the region, or domain of everlasting trost. Id rarified,

and expanded,

it has the greater capacity for abofreducingit to a fixed and latent state. And the higher we ascend above the level of the sea, the air having I he less weight to compress it, becomes the more expanded through its own elasticity j and the heat that reaches the higher regions, is of course more rapidly al)sorbed, and reducecl to a state of complete uiacti\nty. Under the Eqtiator, the Thermometer fails about 1 o in the scale of Fahrenheit, for every 300 teet above the level of the sea ; and in proportion as we advance near to the Poles, the fall becomes more rapid and

t'orbing heat, or

after

we

;

reacli

a certain elevation,

we come

to a point

ineverv latitude, where the Thermometer never exceeds .S2 = , and where ice, and snow are never melted. This is called the Ime of perpetual congelation.

The line of i)erpetua! congelation is sometimes spoken of as an inclined plane, extending frjm the Equator to the Poles and by others .t is represented as the companion of the cvcloid but ne.ther the one nor the other of these is correct. *It is a curved line, but its curvature is not the same with that of the hemisphere; tor it is raised a great way above the earth, at the Equator, and comes into contact with it, long before it reaches the Pole. The following account of it, is from th^ Minburgh Review, No. 59, West pa.v^age, which

an article on the Polar ice, and said to have been from the pen of a distinguished writer. "Under the Equator tlie mean ^''''^' '"^' ^^'^^'^ ^^^*5 in lat. 30 o it is n,. iNorth

Afif"*-

in is

^L^^5"^^

^'^^^' and it comes into contact with the earth If this be correct the line of perpetual congelation, comes nearer to the e^rth at the mean rate cf 145 feet for every degree of latitude. Within the 4

1

at the

,r D Pole. ,

tropics at 283 feet, for between 30 -= and 60 , and at227 feet, for ever>' degree between 60 o and the Pole, which cannot be correct'. ;

ever>^ degree

-

It was perhaps a slip to say, as the writer does, that the line of perpetual congelation touched the earth at the Pole. If lie had given the 65th degree of N. lat.

his stfitenient woiil.l

not in the last part of it have been far from the truth. But I vvould take the liberty of saying that as it stands, no pnrt of the statement is correct. M. Bouguer determined hv actual >«

'*"'

»>

""ving

"""'S'"''^'

"s rapid sweeo i„

J oppS

reTch" thrs^o*''^'^;"-' «-'he North Pole, Westerly direction *2 '^"^ ^ S""*" ; and the culnff '''« S""'!' Pole, •lietime it reaches by the 27 = 'lirection; and both continL ..*'• ""'' " North-Westerly er they approach teCatortin"!^^ ' IT""^ ™™'' "'^ "«"«''«'^/,»"'--'« becomes due West an,l thev thtTTc^t ?l """"" °^ '^e trade winds, o* acooimt of the adv-^w, T""''^ ",'"'"'" "^ *em in commerec. Wer^ there ,„*'

by

time"?,

i? 1T»T

in the tropics! ">" ^lobe, withthe h^^n^^'''^ "'^'''^ pc'for/n the vvhde d 'ct t of it" r ,"f "l'' ^'""^ gress rotmd it, is ' ''«' *beir pro„ intcrceo^P^ >nterventio„ of the «ve

^T^

rcaT

would

continen

s

of

ISf

w

as to

rise to the

exten-

„nS s'

passaga„verthe..eb„SdisWcts

-fied

™"*

•

Si^r™"'

'"'''" "«'!'

^^!^^:^^ ^TZ^J^^'r^^

;;

29

MfiTfionOLOGt.

whence they

alleged, id

see

)t

topics,

and

le

nispheres

^

with the

>

and 4 ® extent of ern,

and

former,

s

ome

into

ng before latitudes,

nosphere nich inimeter of apability tlie tro-

itagonist

sweep

J

opposite

thPoIe,

South'ole,

by

Westerly

this re-

it

at the

centre of the earth, the perpendicular* rising to the surface

tropics,

nd not beagain lo-

And

returned again to the Poles*

base of a triangle, and erect a perpendicular upon

latitudes

*

aj*e

turn to the Poles, it is no hard matter to explain. If we take the axis of the earth from the Equator to the Poles, for the

what

,

at the

of

of the base by 35 miles, the earth being 70 miles less from Pole to Pole, through the centre, than when measured through the centre at the Equator* Then add to Ihis the 25 or 30 miles earth

the

Equfttt)r, will excee»l

the length

more, that the atmosphere rises above the ettrth at the Equa* tor than at the Poles, and the perpendicular will be 60 miles longer than the base, which facilitates the descent of the air from the Equator to the Poles* Being elevated to a height of 4i5 or 50 miles above the surface of the earth at the Equator,

and not being subjected force,

it

naturally falls

to the full

down

influence of the centrifugal

the very steep descent towards the

and performs the same circuit anew* This continued circulation of the air, betweeti the Eqtiator, and the Poles, serves jnany iitiportant pui*poses in the economy of nature. Among others it contributes to a more equal distribution of lieat over the GlobCj and what is of no less importance it tends to preserve the purity, and salubrity of the air. As the blood when returned to the lungs by the veins, is no longer ^i to be sent baclt into the system through the functions of the arterieS) till it has been previously relieved of its Buperabundant carbon, and has perhaps received a proportion of oxygen, so the air in its passage over the earth, towards the Equator, becomes in different respects deterioratedj and impregnated with a variety of noxious qualities, but its return to the Poles,

Poles through the higher regions, and subjection to the action

e near-

of th« Polar

3comes

those important pui'poscs which it is intended to serve, both in tlie animal, and vegetable economy of nature.

winds, 1

com-

5

with-

winds r

proextentheir

and Ymrm

sd

frosts, purify

The second for,

and

class of

and

refine

Winds

it^

and

prepai-e

vVhich I proposed

it

to

anew for

account

are those that are constant in their motion, but changeable'^, periodical in regard to their direction.

The

chief of these

Monsoons, which blow one half of the year from the North-West, and the other half from the South-East. They are only a part of the Trade Winds already mentioned, are the Indian

but subjv^ct to the control of local influences. I observed im frgird iO iliC Trddu Winds, ihat ilicy come from opposite quar-

C

.10

METEOROLOGT.

^P"'—

"",'"' °«"'" ''" T:.e reason of h^i; hara^M ?'"vernal equinox,wben the sun crosses the line ^ml' Z'i'"'^'^'l'f

M t%^^htotShTr;'"' 'T?? -i-^^^^^^

Ti.o forme

tteS asceEo"';:;,5 "^

t«r rushes in

"flatitude, t'.e

toTak^feT;,

.'"

'

''""^i^^

"''• IS drawn into the vortex, and if light enough to ]ye lifted up by it it IS

rolled

more closely

pid wiiirl. fipout;

and

When if

it

happens^ as

and

fro,

and carried upwards it

in

a ra^

fc^rms the water*

ver>' fi-equently

does on extenof sand, xvhidi move over the desert, according as the dirterent currents

sive sandy plains, to

together,

tins takes placo at sea,

it

it

raises lofty toliHnns

preponderate, tmd when at last it dies away, a large pile of sand IS lormed, which has been known in some insUmces, to bury a whole caravan in its fall.

Of the variable winds, one from tl>e Soutli, is tire most common in the Northern hemisphere, and one from the North, in

the Southern hemisphere.

In Euro])e the wind blows from ilie Southwest, about 126 days, or one third of the year ; and diflerent hypothesis have been formed for the purpose of accounting for the circumstance. If I may venture to give an opinion of my own, upon a subject on which men of the highest respectability have speculated, it is this ; that Soutl er^ winds are occasioned by the Aurora Borealis, or Northern Diflercnt theories have been formed respecting this Lights.

ly

remarkable meteor, but that of Dr. Trail appears to be the that while different processes are go; ing on, on the earth, a proportion of Hydrogen gas is disen^at^* ed, which being very considerably lighter than common atmospheric air, ascends through its own buoyancy to the upper surface of the atmosphere, from whenc6 h descends towards

most probable, namely

where it is collected in such qXiantities as to be ig^ by electricity, as it comes in contact with the oxygen of the upper regions. Supposing this to be the fact, there will on •every appearance of the meteor be a vacuum created in the almospliere, by the condensation, and burning of a poilion of and that will give rise to a Southerly wind. Now the gases known fact that the Aurora Borealis is generally it is a well followed by a Southerly wind, at least in the higher latitudes, and that the farther North, this is so much the more common. When the meteor is brilliant, and rises to a great height in the tlie

Poles,

nited

;

9S

MBTBOROtOOYi

T „.

»

*1

l>n.

;.

a

less effect

to „rremoved f*"""^?" •" phcre, teing

on the lower strftta of the afmof but a greater distance fromtl.emj

J

^^

^^|, ,,ef,„ed in

its

upi)er

'*"^>"';IiTmX'f««ov^S by» SoutlK^ly wind, and wind depends on the ^'^*"'"''i%rj r it ?'?• ? rmeteo* from ms. Sometimes

I

,

t ra^ther :^Sh w.Uim Z'b

*'

nouis

«'of thP .r

w ,m"n^lS

ii:;e

and not unfre^uently first, m tlie inimoves nlvvavs l»te.t a. the and •cha.^ge, ofte it is

trn,es

,

36

;

in a cana .s move.1 from it j.i^t as the water the gate ,s opened when lock, ourhood of a tt sHccession, till whati9nexttoit,aml soon in and 'Xrd,at 7*' ''^''" When farthest extrennty.

Hi

i

1

»«f

ZZ tSl

,„j,,i,e8 ,o the

nearer to us ;:ligh,er, and consequently but when it sooner, „ in ,l,p wind will reach us the if the distant, more " consequently ""f rfand ttv^ and propon.onally be w.ll all, it

;

;:

,

^hC-ct'ur

latitude at

Aurora Borealis will be account V* well foimded.the nature, by which a complicated machinery of Jn( of the compnc a part atmosphere of one region,

'"Ifthis

raTat^fCrrt-air^^^^ f

1

the '

place. made tlmn would othewise take winter the in r^ vercc^nuSn in tliis countiy lit i«

—

for

the Northwest, wU t^bCLtn a

*-

"

season, for

'->•!

»;

-f-

^;"—^f Ihilh V^

trand that with

"

":* wind. It is easy to account ram oy a^ slterlv .^^„p,.„t„re. its"tumly lowed in \Ts The floatir.g or d^imujon^^^^^^ the gradual

r*

-

^.^^ ^^,^J^^

for

active heat, ''«'

" '',f

restored, or

XaUas been tenperataie 'TTZZ^m^el^^^^^'^^--'' phed, the wo whieh the Wo V termina^,

S"™atX"b Ihe greater me

ui^

t\\Q

ranfied

vv

uuuo^uofe

its

place sup-

For the calm in ^^^^^ may be as-

low.

gave s„„j,,„,^,j „i,ieh

ott:4%outh,the

more

-apidly is

r^^^tnnnllatitude^, forced up^^ vi d^^ -^i" ,,

56

METEOROLOGY.

wards

higher regions ; and its greater accumulation hasten itw detjcent again to the Poles; while the cold air from the Poles, has been precipitated on the South, and diminished the temiKjrature of the warmer regions, the air from within the tropics has taken its place ; and though cooled in its passage throi gh the upper regions, it is still warmer than the air about the latitudes of the Magnetic Poles, and even to a considerable distance to the South^^ard of them. to tlie

tliere, will

I have thus pointed out the principal causes, by which the equUibiium of the air is disturbed, and currents of it are put in niotion ; and in so far as these are known, they are ascertained to be, an increase of the tempeiature, or a diminution of tlie quantity, in one place and not in another.

IV. It will now be proper to pay some attention to the Moisture of the atmosphere, or the quantity of aqueoifs vapour coniained in it ; tcgether with the manner in which it

and afterwards retums it again mosphere contains a proportion of it,

ted

to

the earth.

v^•ater,

is

receives

That the

at-

universally admit-

but different opinions are entertained, resjiccting the state it exists in it. Some main tain, that it is held in a state of solution in the air, as sugar, and salt, &c. are held in water; andothers, that it mixes or combines with the air, in the state of steam. It would be going outof my -way, in

;

which

to

ter into this controversy,

and

I shall therefore

en-

take the latter

opinion for granted ; as it is certainly the most common, and appears to meto be the best supported, and most probable of tlie two.

When a

quantity of water is exposed 1o the -air, its volume, gradually diminished, till it entirely disappears ; and process is continued under different degrees of

•or bulk, -this

is

temperature be warm or cold. Indeed it may be a question whether water is most rapidly dried up, in an intense heat, or in an intense frost. The atmosphere then, is continually receiving a supply of water from the earth, in the form of vapour but there are times v/hen the process of evaporation goes on with more activity than at others. It was ascertained by the experiments of Halley, that water exposed to a or whether the

air

;

•

dimmer

heat, loses

by evaporation

cubic inch for r«>quently

tiiat

in the course

of twelve hours, one eveiy ten square inches of its surface, and conevery square mile of water, loses 6,914 tons,

37

METEOROLOGY. muiatioti v'hile

the

of tons 1.. the same time. tl.e 01ol»;, .e,..ns of the .nf.K-0 of ot 'l'^' *•-' " >. ulea an erclwilil water, we n-ayfonu a un.m evaporation, ol means air, l>y t'lut i^ elev!>t«l into the tl.e w.nter sca*.n, is it Ami ay ue ns f,x,.,ts, water dr.es u,, «.vcre in !;;, he colder clitnates, for tiieilay. iimrh if notnwre intlieni^lit,llmnni er " l.eat, un.l eol.l, pve a^n of ex.ren,'es .lothe n s(iuare .U'srcc

and every

HZIJ^

33

millioni.

u>^^^ I

e South,

the air

s,

cooled ner than ;h

even

to

^A^^^^^\o.

at

.l.e.v lost

one

tlur.l

of

and

rs;

erature,

ay be a intense

ontinuform of )oi'ation

jrtained

l^tnmer

one con-

irs,

ul

14 tons,

its

l^tween

density,

U^

Col du Oeant , «>"! "'» »' ^^ nova, and the sumn.it of the evaporalum of "%«'''"17^' latter place, the rate ,7,^ !.(• ;/ ilus to 3 ; an. Iron, former, was no less than as 7,

at the r » of the air lor ,'e'f' v,n, vap CO. eluded, thVt the capacity w.Ua This .s ,h..un,s I.e.. density its as rapidly i..creascd, evaporation which .9 oltenknmvn for the very active On sucti tl.un.ler shower. lotakP .ilace. after an eleenic or

SL

covered w^^^^

^:^,LI.t^;:..rfaee ..f the earth is often disappeaiv. vvhirh rises a little above it, am'

a ncnt preserve the sahd^n;rision of nature, 'and .e,.ds to tc.hexte.isive changes .n the A.1 sudden, «..d tv of the air. atnma to both danger, ,l.^tm^ of the air, are preg..ant wiU. al establisl.e.1 checks upon are he.^ but V,fe Tnd ^ctobte and valves, safety of purpose » "h -ere, U.e 1 Ins is

:dl

Xese

S^

any

of an over act.on, .n us Iron, the consequences greatly state of the a.r is the When of "he "y«te.n. ..ce» pro. co.n.njmly i. electric discharge, it very

nmwet .art

ha..wd by volume,

,t ,« ai-o !-•""*'' 'J Sanssnro aseer.au eU,

l.t.t

which

i.«n.e.hately

Mlows

evaporation ,i^^ 'and the eopious engendered, for of l.eat that n.ay te excess ir takes off tte ot caabsorption g,^ater attc.deJ with a

tefarfew

changes

state.

into a gaseous loric, than that of water .le,«..d« '" ^«or avera^ tl.e mean where regions, temperate I., the tion. evapor^ «f Fahrenheit, the annual ^ ^nt^rature is 'emperature .» mean = the lat. where 10 N. in but inches, 37

™

A

h'J.

• 9

the -dunuai eva^xjruuun

«

»"^*v

v.

-

-

-

38

JtfETEOROLCGT.

When

water has been converted into vapour, its volume, or ]es;s than 1800 timc^•, by the charge, and consequence of this extraorchnary exjansion, it becomes

'bulk in

is

increased no

tlK

proportionally lighter than air, and r\^es to tlie higher regions of the atmosphere. The vajjour sonietiniee aj'jxars fioni the to]) of the Ancles, to be susj.enilcd over the pacific ccean, at

the height of 10,000 or 11,000 feet but at other timers ; •doudfi are seen floating, at on elevation of several thousands of {ci^i, above their highest MiniTnits and it is well known, ; that tlie niott lofty ^eaks of the Hinurnlayan ridge, are crowned w-ith e\'erlastir.g frost, and snow. This rise of aqueous vapour to tlie hgher regions of the atmosphere, is necessary for tlio supply of brooks, and ri'v^ers, which have generally their s«>UFce^? in

^

the Ifgher grounds, and

which are of essential serthe inferior animals. So far as i kn(Av, no tlieory has >et been proposed, that will account in a clear and sattjsfactorj- manner, for all the pheno-

man and

vice to

all

mena, attending the condensation of vapour, into cloudp, end descent to the earth in the form of rain. Sometimes tlie heavens are overcast with clouds durirg tl>e night, and clear through the day and at other times, it is the very reverse. its

;

One ment

thing is

certain, that

it never begins to r^in till the firmaeither partially, or generally overcast, and the invisible

is

moisture with which the air is saturated, has become- vesicular. Moreover, it seldom, or nev«r l^appens, that the atmosphere becomes gradually dark, or that tire 'charrge coimmences with a jiglit, and igeneral liaze, which gradually thickens, and be-

comes

closer,

till

commences. When those chargea which are followed by fain, have an

the rain

in tlie state of the air,

commence in a particular place, appearance, which is gradually iitcreased, sometimes by its own extension, but more frequently by the addition of other clouds, which start vp around it, ami one after another, become connected with it. But when the change which leads to rain has not an electric origin, the clouds do not arise in the quarter tcwards which the wind blowg, but rather in the quarter from which it comes. This is more electric origin, they evidently

wl»ere a ck>ud

makes

especially the case,

its

when

the

wind

is

Southerly.

On such occasions, there is usually a darkness in the southem quarter of the heavens, which rests on the horizon, and .fis^s to

a greater or less he'ght, according as

it is

nearer or

more

with

39

KBTE0R0L0C7.

approaches nearer us, a number of overtlje fac«ofit, amUUfmct clo«;l., appear to arise succession, towards the north ; and take eir Bigluin ra^id form larger they frequently increase, and th^ cou^e of wiUch gomg on this ,* cLnsmute the whole of its 'lotto to -°tiofThe of the glotw the whole surface cover would much water as the of proportion small only a depth of 3* feet. But it is and that proportion can te water, int.. convertible is is » compound of i of oxWater ascertained to a nearness. acertam proportion of with yrn?and S of hydro^jn, combined adds nothing to its weight. of o^ythe parts contains no more than 21 of 63 parti materials for the formation it can onlv afford o its supposing that the whole

eame dimension?

Set Se Sr,2t

EwhUbei^impondemble,

Srair

Z rtheloSofvUer;

m

WO

oxy^

could be found m sufW3 e so appropriated, and tl«tt hydrogen *. up the compound. But as such ficfent quantity to make faU^ instantly be would althis, were it possible,

~^nt

of v'tahty, . is out of .^ thing possessing a principle of reasonmg in th^ necessity no But W3 are under question. compound with which we are way, for the air like every other and has b(«n subjected to a acquainted, can be subjected,

toev^y

V

^

Z^' i-

i

40

METEOROLOGV*

chemical analysis ; and tliere is no knotvn process, l)y which greater annount o( water could be separated from, or formed o\it of it, than would \^e sufficient to cover the surface of the Globe, to tlie depth of 34 or 35 inches and even this could ; not be done without decomposing it, and rendering it

a

unfit, for

•the support of

Now

it

animal and vegetable life. has been fulhr established^ by observations

made

and

often repeated in different parts of the world, and by many tlillcreni individuals, that not more than 34. or 35 inches of rain at an average, fall upon the earth in the course of the year, in the temperate zone. It appears then, that the rain which falls

m the temperate

zone, in the course of the year, is the same amount with the quantity of water contained in the air, at any given time, or which could be sei)arated from it, by decoml>osition, and that it is two or^three inches less, than the water which it receives in the same region in the course of the year, by the process of evaporation. This is a curious fact and I do not know that it has hitherto been noticed, or that any one has thought of enquiring into its cause. in

The s a.ntity of rain that falls in some parts of the torrid, much greater than that which falls in the temperate zone

is

and

;

not a ditRcult matter to discover, both the cause of this also its design. I have already shown, that owincr to the greater heat, and rarefaction of the air in the It IS

and

Equatoriafre-j-ionf!

annual evaporation there, is 100 inches, or upwards, while It IS only 36, or 37, in the temperate regions. And within the tropics the average quantity of rain^ that falls within the year, mounts accordingly, to 100, or 110 inches. The rate of evaporation, and the quantity of rain in the different zones, thus appear to correspond nearly with one another. In the teniperate zones, the rate of evaporation has been given at 36, or 37 inches, in the year ; while the quantity of rain has been stated to be only 34- inches. But the difference is easily accounted lor, by the fogs, and dews, and drizzly tJje

;

rains,

which

cannot be atcertained by the Pluviometer. It may perhaps be thought, that the excess of evaporation over the rain that falls the temperate regions, goes to make up the more abundant ram. But this cannot be the case, for the moisture '^hat falls Within the tropica, must be equal to that which is taken from the earth, otherwise it would in time he entirely dried up but two or three inches in the year, da not seem to be an over-

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MBTEOROLOGY. allowance,

for thQ fogs,

and dews, &c. of the temperate

re-

regions, render a great^'^The greater heats of the Equatorial support of vegetation, the for er quantity of rain necessar>', is required ; and water which for ^nd other important objects to the ratv\ proportion near a bear always the fall of rain, must burnt up while be might earth the otlierwise of evaporation, with moisture. Acthe atmosphere was altogether overloaded being equal, Uieve is a cordingly we find, that all other things heat, of any parallel mean near correspondence between the In the Island ot it. in quantity of rain, that falls

and the ® N. lat. the annual ram amouuta Grenada for instance in 12 42 9 to 36 inches, and at St., in to 112 inches; at K^me inches. ® to 1,6 ?etersburgh in 60 ^ .. ^ „ i i falls, on. the higher Moreover, a greater quantity of ram to the level of the sea. grounds, than on those that are nearer at Rendal, m the While 34 inches fall at l^iverpool, 60 fall •

.

The obvious reason of this is, and settle on their mountains, that clouds are attracted by the air continues while rain, in out summits, where they fall like every thing arrangement, This dry in the plains below.. observed, it already have I as for use its has ; else in nature, streams, running that springs, and is in the higher grounds the mishow to time, of oriainate; and it would be a waste mountains of Westmoreland.

portance of providing

for,

their

constant,

and regular

sup-.

^'

measure confined to Within the tropics, rain is in a great This is owing dry. is other the while one season of the year, the Northern hemis he When sun. the to the situation of and the tropic of Cancer, the isphere, or between the Equator and to the S.QUtli of the rainy season is in the same quarter, the Ime, and is beEquator it is dry and when he crosses ramy season is to the Capricorn, tween it and the tropic of Between it is cky. North the to the S. ith of the line ; and Norththe m season rainy the therefore April, and October, is April, in the and OcU)\)ev, between and ern hemisphere, The cause of this mostprobably is, diat while tlio Southern. more efiect there, «un is on the one side of the line, his rays have from the Pole, in current and less on the other, and while the of the temperature increased the former, is diminished by the dimmishthe by increased latter whole hemisphere, it is in the

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