1000000031

1\1

thO! b,,:-.:

tl,.~ in~·l

;r.cJ

t;olumn \ve do not mean the bottom

of the

inc!iocd

tuhe, bUI lhe

loweíl horizontal

(eétion of

"fhus.

lile

conl:¿cr

lhe

fuoface

FG as a

pl.lOe

paffing

througll

the two tub:s

and E,

thls

phne

wdl cut {he

lubc

pu–

pend"ululy. and the tube E ob! iquely. But a perpeadicu.

lar

f~lhon

cylindcr is a ci rele, and an olJhque fl.....:tion

Ilf it is :ln ell ipfts. Therefore tbe bafe of lbe ereél columo

1';

circuhu', aod the ba(e of the inclined lube

ellipucaJ.

,Now,

the

fllppoGtion, lhe

twa lubes have

equal

dianlc–

ten.

and confeqtlently

the (h.qrter axis of the ell'ptical baCe

\ViII

be equa.f

the diameter of lhe

circular

one.

There

anotber

fOIl

of ínclined barometer,

fu~h

an one

.s ABR .

(ihi,/.

6g. '7.) wbicb is ereél fur 28 inehes from

H, and {hen is inclined from B

Toe

roercury

will

n.tnd

tbe

Carne beight in this barometer, as if

had

ceco a Hrait one

for the ('olumn of air prclJil1g at the

bafe A would be tbe

r.me

io eilhcr care: aad tbougb lhere

more

mcrcury.

in the

t ube

ABR

th an rhere would be in

'lhe tube ADS: yet. ruppoftng tbe mercury to rl,nd at lhe

lame

le\·el

in eithcr care, the prelfure of the mercury

down'''-Olrds wdl

either rare be the fame. For, (he pree

fure o( Huids' is as tbeir bare and perpendicular height : and

llere the bofe A is the fam e. and the perpendicular be'gb, i,

tbe fame. whether the tube is creél .11 the ",ay up .. AS.

"r i. inclined a, ,betop as ABR.

Tbe advantage wbicb is propored by thefe diagonal ba-

10mcters,

as {hey are called, is

make the ViHlªtion of

the ")eq:ury greatc:r, and confequently more apparent, "'pon

a givc" change io the wealhcr. Thu, fuppofe AH or 28

inches to be ,he leafl heigbt o( the mercury. and AO Or 31

Ínches to be thc grearcfi hcigh l of it : _then tbe whole vana

~ion

<viII be within the C?mparS BO. or 3 inch... Bu,

the baromerer, inflead of being erea: ar the top, is incJ.oed

into th: pofition

Be;

then. as the mcrcury Jhnds al the

fame perpendicular height in this diagonill baro'Hecer as

an ercCt one. AB \Vill be the Ieafl hcigbt, and

ABe

w.U

he the greatell heigbt. lince O and

are-

0 0

the (ame le–

vd or at the- (ame perpend.icular difiance from

Now

though BO : one Gde o( the paralJelogram . is but 3 inches

long: yet

may be 30 incbes long. or more; and coo·

{equentl)' liroee AB is lhe l..

be:ght, and

ABe

i, ,he greu·

dI: hc:ight, the variatian of Ihe Olercury

will

be much grcater

tban in Olo ercél barometer; in panicular, if

is 30 toche,s

]ong, the \'ariation will be 30 ¡nches inOcad

3, or will

times greatcr io the diazonal barometer

tluo

would

have beco in an ereét one.

T h, harom,la jlandr al Ih, [am, papmdicHlar h,ighl.

""o,lh" lO,

f"c,

IRTg'

[mall.

Ihe mercury CJa'nd, a' tbe rame heigh' either in the

large tuhe

or in the rmoJl tube O . there mull be more

rnercu,)' in lhe Jarge one (han in ,he (maIJ one. BUI fince

1he heights ale equal, the quantities c..fmcrcury contained in

, befe lUbes wilJ he .. ,heir bafe,. Now lince tbe rolumn,

of air,

which ,he rnercury is fupported in there tubes,

are as the refpeélive baft!s of Ihe tubes, the columos o( air

will be proponional

1he weights in each lube, wbeo the

perpendicula r ht ights are <qua).

But though the heigbts of .he mercury \Vould be the fame

in fmaJl ,ube, as in large ones. if, as \Ve mull fuppofe in

,he propolirioo. the mercury moved equaJly (ree

both :

')fe

f3d .

upon any cha ngc of weath("r, the variatíon will

~ great~r

in a large tube Ihan in a fmall ooe: becauf., in

l.tr

ge robe, the

wcicht

mercury

i,.

grclt, t'har the mo–

tion or

wiJl

not be hmdered

by any

attraétion or repullioA

of the glafs upon

it;

whena:, in a fmal1 tube, where lh'e

v.elght of mercury

kr.j,

thc aélion of the

J\ht's

is c(}flGde–

rabie in plllpOrtlun tO

that wcighl,

and ,confcqué01ly (he

variations

wtll

11;(5

upon

g:ven'

chang~

of the wtclther.

The éarOm(l(r will comino,;,>, be Ivw in rain) "W(olht r .

From what has becn faid alre"ldy about the barometer, it

appt:ars, thdt the mercury wdl bt: low. when the weight of

the a:mofphere is dimIOlI'

h.ed

;, and filen a diOlinutlon of

the atOlofrhere \VdJ occafion rain , Therefore, fince rain

is occafioned bj' the (ame cauCe that makes rhe mercury fall,

the barometer wdl commonly lland Jow

ín

ralDy wcather.

T h,

6ar01l/,lu

i",

lo-wdJ cí

,,{{

in lIiolenl jlorf11f

,",illó.

\VheD rhe air movcs

hOI

iznntí!. lIy with a great velocity.

as ;t does in violem Horms of wind, 'us weight. or nther in

prcffure downwotrds

~ccafioned

by itS

welghr,

will

be dlmi·

nilbed . For as .ny h,.•vy bod y may bave fu cb a veloCl!y

glven

¡t,

when it is tnrown down

honzootally~

as may

{i–

[her carry it quite off (rom ¡he eilrlh', centre, or fuch ... ve–

iocny as wíH mOlke

mOfe round the e.lrth in a cirele with–

Otlt c:ither dt"p.u ung (rom the cent re or approOlching

every degrC'c of velocity given lO the air will make

teni or prer. lefs tow.trds the ccntre; and for this reafoD,

as the mercury in the bafon will be lef. prelfed. ,be heigbt

of i, in the tube will be leC. in fiorms Ihao it is any Olher

time.

When

ajloT'1ll oí'Winó hover, 1M

mtrtury

'Will

rifo ""y[aft :

Becaure as the horizontal velocity of the air ceafes. the

pr~lfure

Gownwatd. will be fuddcnly reOored. and conre–

quendy the mercu ry iD ,be baromc,er will keep "Gag-as lI,i.

prdfure is reftored.

THE

·THERMOME-TER.

T'he

,varia/it;nl

differtnl Jher11lorneJerJ are

ftldof1Z. (qual,

upGn

((Jual variaJ

ior.i

heol or cold.

THERMO METER.

is a weH.known in(lrument fordH..

mating differcnl negrees of hea, or eold.

eonltrh of •

,ube or Hem. with a hollow ball at one end

0 1

it . The ca·

·. ity of the ball, and par! uf lhe tube, is fill ed witb Ipinuof

·wine. or with linfet'd oil, or with mercury, The upper

eod of the tUbe is commonly f<aled hermeucaJly. But in

(ealing Ihis end, the liquar in 1he thermometer is

raré6e~

heating it till it .Imoll f.lls tt.e tube; fo tha, wheA

is reakJ , "nd lhe 11quor contraéls' agaio as it cools, tbere

will be a ..euum Idt in the upper par! oT the tupe.

ADy

of there flu ids will ral« y by ' heat , and will conu"dél again

when tbty cool : and conle'luently in wOlrm weather. the

fPll its, or !he oil, or Ihe mtn::ury. whichever th Iherma..

meter is made off wilJ ft Olnd highcr than in cold weatl'er.

Thus far tbermometers ",ay be faid

vary alike : th,y

will either

f'i(~

or fink fror.1 the lame caufes, BUI tbc:n, up–

on an tqll.d mcrcafe of hcat . they leJdom val

equally.

though tlley "re! n ade of the J"me Jiquor, One:

tbc:rmo~e

ter

lnade with fpirits of wine

P.lay

v'4ry upon an c:qual

crt:are of heH

m~)(

h more

lh.ln

another that is madc:

wlm

the rame fon of fpirils : fo tpat If one

raJes

iDCh,

anO-

ther

Olay

rife but .;. or

.¡.

inch .

Tile variilion of a thermometcr i$ dircélly as the c.'pa,"Y