1000000031

The w";ght or prclru re of the air is

,,,,31,

dctcrmind by

'the fo!Jowing

expcriRlenr.

T he

TO R IC Ii t.LIAN

EXl' E RIMENT..

T ake a\

gla~~ tub~

t¡hout [hree.: f( et long. and apeo at one

tnd : fill

wllh

qUI\:kfJI ...er ; and puu ing your

linga

upon

the ope'n

toJ,

tUI

n [hat end d-,>wllward and

il1lml.!rfe

¡nw d

fm .d l

vdrel

of ql1icklilvcr,

WlthOUI

Jt:tting in any ¡ir: (hen

aw~y

your

IInga,

and the quickGlver wdl I'emain fuf.

pended io the tube

¡nches aboye

furf.lcc in the

;vt'f!d; fometimei more, ami

'2t

otbe,r

times J((s, as

lhe

welgh t of Ihe:

¡Ir

v.ried

winds and other

cauCes.

That

~he ~uickr.lvú

is kept up in ,he

tu~e

by ,he prdfure of ,he

atm~rphere

upon

lh.l\

¡.,

lhe bafon. is cVJd<nt ; (ur,

the

baf~n

and rube be

P~[

unJc r a glafs, and (be air be chen

raken out of [he glals. all dle

qUlckfilver in lhe tU'>e w,1I

:fell! d own in,ta l he hafon ; and

{he air be lel

agel;n, the

.qlllckfilver \ViII rife

(he f04me heigh{ tl's befCJre. There–

(ar~

lile

~i~'s

·prd fure. an lhe

fu rfclc~

(he c¡rth, is

t:quJI

tnc welgnt

29!

Inches uepth af quickfilvl!r

oYer tbe

nnh',

fu rfelce ,

a mean

rat~.

.fqu4re .c·olumn ,

~uickG lver. '9~

¡nches high, and

,~~e

,"ch thlCk,

\~l!lghs JU~~

paunds, which

equal lO

,tn.!

pre[furc af alr

~ pan

cyery

~u.He

inch of lhe

¿..

nh's

furface

an,1

times as much. a r 2160 paunds,

UpC.lO

~very

fq uare

rO~t;

bec.lufe :. fquare foat contain,

144

fquOire

Inches.

\lus

ral!!.

midJle-Gzed m",", whort fur(ace

",ay b. abou,

f9u~re

f<et, furt",",

a, prelfu~e;'f

; .0240

pllunds,

w~en

rhe alr

of a ml!an

g~avily

I a pre{fure whlcp

:wculd be It)fopponable, and even tatal

us , w:re it not

t9ual one very part ,

.u~d

ccc rilerbalanced by lhe fpring <.tf the

alr within

us'.

which is

dlfFur~d , l~rough

Ihe

whole

,body,

and re.aéls ,\VHh an equal,ForceagOt,nft lhe ou(ward prclfure

Now fince (,he eillrlh's furface contains '(in round

n~m ·

bers)

:200.000,000' fquare miles, and c.very, fquare miJe

27,878,4°°

fquare feet,

ther~

",uH

5,575

,680000,000,

000 fquare

(eel

on the eanh 's furfrlce

which

multiplied.by

2160

pound, (the p'elrure on eaeh fqua re foot) gi vcs

12,

043,;68,800 o" o,000,000

pound, for the prelrure or

w<i~ht'

of tue whole

a~mo!vhere.

\ Vheo thSend of

pipe is immerfed in

~'ater,

and the air

as tak..:o OUt of the pip: . lhc' \'1.1tc r ,\ViII rife in it

the

height of

feet abo"e ,he furia" of the wat'er in which it

¡,

irnmerfcd ; but will go no highcr : for it is round . IhM a

,common pump will draw w.uer no higher than

reet a_

b~\·c.

the

rurf~ce

of , he \\'ell : .Ind unlefs the

bu~ket

goes

\V1I~1O

lhat

ólfidn.~e

from , he weJl . lhe w:uer wi lJ nLvcr cet

ab~ve

it , N o,,', as it is lhe prd fure of lhe atmorpbere, on

(he furface of lhe U'ñter in the \Vell, th;:at caure, (he water

to a(cend i.n lhe

p~,mr,

ann follo'.V lhe pifion or bucket,

.whcn lhe alr abov!!

is lirceú up ; it is cvident• •hOlt a

ca·

J~mn .of walt~r ~3

reet high , isequJI in weigh t tO a columo

or qU.lckfih·er of the fame' dilnletCr

291'

incht. s high ; and to

tlllck a column of air, reaehing from the eanb', furface

lO the top ofthe atmoípbere, S1..e

J-IY.DROSTATIC,.

THE

BAP.Ol

'vll::TER.

(erene c:llm

w(,3t~er.

lhe .ir

n~s

weigh r

~nongh

(upPOrt a column o( qu,ckr.lver

in::hcs hil::h : bur in tem–

p.cfiutlus (lormy we:n her, cm :"ul)ve 28 ¡nches. The C]u¡c!c'

filvn. lhu5 rnpported ·in a J!lars

'ub~.

it;;

founn to be a n:cc

count: rbal~ne(' .

to tllt

w ...

:gHt

or prdTure of Ihe A;r, and lO

Jh~\V

aherltlO" a' diJf" ,nt time.,

Acd

bein¡; ncw ge.

4 RS

nC'T'iJJy uft d to denote the chilngc! in lhe weight óf 'lhc Air,

and

l :)C

weather eonlcquent upon lhem, it i5 called

[he

6urom~((I',

or wealher· glar,.

Ti·, 11/u cury

'1·;/1

/ll1nd

Jh,[ame

ht!Íghl

eitlur

QII

in.

c/rned

6arouu/~r

in an

er~él on~,

. Ifthc mcrcury at any ,ime lland.., the height of 30 inche'

'~the

b.rom<ter D , . (Plate CXLV. c,g . 6 .) thenby. incli.

OI~g

thlS baromeler

lnr~

the po(jtion

the

pc: rp~nd

¡cul.lr

h"ght ofthe mereury wdl no, be ahered;' for it will IIdl lIand

the height of

inches: fo th;, if the 'e"e1 AH i,

30.

IO :hes f'om ,he furface

FG,

the mercury will fland at thi.

leve', t ither in the erel'l tube

~ or

in lhe!

inclin~d

one

E~.

N ow here it is

e.,ide~r,

Ih u if

i5 the height oflhe'Oler:

eu ry

wh~n

th('

rube

ereél, aod

is the height of.the

m~rcury

In ·

the f"Ole tube or an equal one when ¡t. is in–

chrred , (here: mufi be:. more mercury io the incliDed tube

than (here is in the ercét one, F or we may conf,der

the Gde, and NM.s the diagonal , of a

ri~h,· angJ.d

paralldo.

gramo

,he diagonal of a righl angled

parallel~gram

is·

Jonger Ihan

the.

(ide. Thert'fore,-Ihotlgh elthtr

are

t~e

f,me perpendicular

~ltrr,n,"

froO!

FG,

yet

NM will

long~r

llt. n

N~.

Since ¡hen {he columo of mercury

longer

the I.nclmed

Ihan in the creél one, lhere will

b.e

mort mer::urylo lhejoclinedlhan in Ihe'ered one. The q ue'–

fiion therefore i" How thc prdfu e of (he atmurphere ca.Q

fuppon a greattr qU3mity of maUer in one Gtuarion of the

~ub~

rhao

lhe olher. W e e.lonot fa y,

¡hat

though in Ihe

lnehoed IUI)e there i5 a gre';:aler q uaolity of mercury Ihan

the crea one,

~et

pa.re

of this greater weight

will

be fup_

poned by tl'e (,de o( the tube as

I,y

.n iucllOed pl,ne. The

lrue anfwcr

¡St

tha! the eoJumn of a:r which rupporu the

me~cury

in lhe inclioed tl.lbe,

greater lhao Ihe coJumo

wl)1ch ftlpporu it in lhe eretl one

The heigh, of 1he ca·

lum of air is i,ndeed lhe

(~nle

in bOlh cafes · (or in eithe-r

caf,

i, <qua l t<, the h<ight of the ¡ imofpher:. B ut , he baf.

ofthe columo of air, and confeq uendy i1S weigh!,

is~reale.r

when {he tube is incl'ned lb",n when il is crerl. For the

bare o.f '

I.hé:

..:olulOn 'of air which fupports lhe mercury in lhe

tube,

equ<l1 to as mueh of 111(' llagn2n't mc rcury's

fUI

face

a.s

rhe bJfe of the lul:-e covers ,

No\V,

if lhe di"melers of the

,ube, D aod E 3re equa' ; ,he bare of the inchned ,ube E

will cover a greélter pan of the fur(ace FG· th",n Ihe ereCt

tube

covers, or the barc of the t"ube

\ViII be grea ter

th, n ,he b,fe of the tube D . For th< contents of the in–

cJioed cubc are gre;u er thim lhofe of Ihe ereét one, as has

beeo

"lhe,vn

a'lrea~y-:.

But Ihe colurrin' of mercury in e;:ach

of the ,ubes are cyhndea of the fal1'o height .. Therefore

.he" baf., are

their eontentS . F.u• .

~ :

XI!. prop.

Since (hen Ihe COOlents or lhe: weighls af n¡ercury in each

tube H e as their

b¡¡[fS,

wh~n.

Ihci r heighls are equoll; anti

the hafe of lhe column oral r, which....fuprorts Ihe mercury ,

aod conrequently the wt"il!ht of Ih is column

l •

is prc portion..l

th~ b~fe

of the tube; it follo\\'s, that the

~eight

of lhe

;ur wIll aJways be proportion",1 tO_ lhe wt:ight of lhe nler·

cury when

ftaDds at a ¡;iven height, whtthcr lbe,lube

';nclincd or erctl·.

Thou~h

we have here (h'ewo, th:lt the Contenu of lile in·

cJincd tube are gre:uer than Ihofe of the ere{t one, Rnd con- ·

f<qu~ntly

th•.t their bafe, muJl be unc·qu. l, Gnc< ,hcir per–

pendIcular hClghls are lhe f.une

it will not be impro.

per

nlew wh;:at we me;¡ n

the bil re of Ihe ,indined tube.

or' ra1he-r of

th~

inclined columo " f 1'¡1ercurYt anJ'

~·hy·

,h;s

Ibculd be grc.ter than tbe ba:e of tbe ere(\ on,. N olV

tIu: ,