1000000031

brokc ioto fm all p:\rts,

tl:\?:y

cannor be

mace

to Ilick to–

gethc:r a!!ttin

widH;U:

bl!;ing

fidl.wetted:

lhe

repulGon

bcing

loa great to

admit

re-union.

'1~he

repell ing force

Lenveen

w:\ter aod oil is fo great,

t hat \Ve find ir

almon

impoffi~lé'

mix thl!m fo as

n Ol

la reparate again.

a ball of

light

wood be

dipt

in oil,

and

lhen pUl

ioto w;u er.

lhe w.Her

wiIl recede fo as

form a channel of (ome dcpth

.11

around the

0.11.

The repulfive force of lhe panicles of air is fo great,

that they can never be brought fo oear together

con–

denCation as to make them Ilick or coheTe. Hence

¡s,

t hat when the weight of

lhe

in..:umbent atmoCphere is

la–

ken off from aoy {mal! quantity of ai r, that quantlty will

diffu(e it(elf (o as to occupY (in comparifon) .n inlini<ely

gr.eater portlon of {pace than

did befare.

AI/ra{}ion

graíJilali"n

is that power by which dif-

1aol bodies lend lowards one anorher, Of this we have

daily innances in lhe falling oliJ>odies

the eanh. By

this power in the earth it

is~

thae bodies,

~fate\'er

fide,

{.JI

liDes perpendicular

its furface

an~ confequenl.

Jy, on oppofite fides, they fall in oppofite dITeélions; all

towards the centre, where the force of gravity is as it

\Vere accumulated; and by ihis power it. ;"'thiott bodíes

0 0

the earth's furface are kept to it on

all

fides, fo that

lhey cannot fall from it. And as it .él,

"POO

. 11 bodie.

p~oportioo

to their refpeéli ve quantities of maner,

wilhóut any regard to their bulks or figures, it aecording.

eonllitutes their weight. Hen:::e,

lf twO bodíes

which

contaln equal quantities of matter,

were place:d at e:ver fo great a dinance from ooe another,

aod lhen left al liberty

free fpace

if (bere were no

other bodies in the univerfe to affefl them, they w,ould

f,1I equally (wift IOwards one another by the power of

gravíty, with velocities accelerated as they approached

each othcr

and wouJd meet in 3 poiot which W3S

haH

way betwecn them at firll:. Or, if tWO bodics containing

uoequal quantities of maner, ",ere placed at any dinance,

20d left in lhe f. me

mano~r

at liben

th<y would hll

10wards one aomher with velocities which would be in ao

,ioverre proportlon

their refpellive <Juantities of mat·

ter ;' and moving faO er aod falter in thci r mutual ap–

p roach, wouJd at Jan meet in

poinl as much nearer to

the

place from which the heavier bony

beg;\O

to fall,

lh;!,n

the place from which the

li~hter

body bogan

f.lI

. as

thé

quaotity of maner in the

form~r

exceeded that

lhe

huer,

AIJ bodies that we know of lia'fe gravity or weiljht.

For. that there is no fuch thiog as pofitive le\,jty,

ellen

in fmoke , víl.pours, and fumes, is demonftrAble by expc·

rimeots on the air-,pump: which fllews, Ihat although the

fmnke of

candle

arce~s

tOl'the lOp of

taJl receiver, when

full of

air~

yel upoo lhe

air~s bei~b

exh2.uned out of the re–

céiver, the fmoke fall!' down to Ihe bottom of it.

So~

-piece of wood be imm.erfed in ajar of water. rhe wood \ViII

Jife tO the tOP of the w,uer, uc-cau(e ie has

:;a

le(s degree:

of v. cight than in bulk of water has

but if the jar be

eOlptied of w:ncr, the \Vood f"lIs lO lhe bonom.

As e\'ery partide of maner has i15 proper gravity, the

effeet of

th:

whole muH be in proportion tO the number of

l he att ratling partic1es; that

IS,

as the C'juaotity of mal·

ter in thc \Vhole body. This is d, monfir.hle by experi.

mcnts

pendulunn; for if

t:1Cy

are

cquat leng"h"

wh.Hever their weights be,

th~y

vi brate in equal ,iOles.

Now it is plain,

d1.lt

if one be doublc! or triple the wcight

of another, it

mufl:

require a doubl e or tTlple power of

gravi ry to

Old.ke

it move with rhe {ame celerity

jull: as

would rcq uirea double or triple force to projeét

bullet

of [\venty or thiny pound weight with ,he fame degree of

(wiftot{s chat a bullet of tcn pounds woulJ require.

Hence,

is evidene, thar the: power or force

01'

gravity is

always p'roponional tO the quantity of malter

bodics,

wh,Hever their btj lks or figures are ,

Gravityalfo, like all olher vinues or emanatíons which

proeeed or dfue from a centre. decrcafes as lhe dillance

multiplied by itrelf ¡nereafes : that ¡s, a body

twice the

dill ..oce of another anralh with only a fourth pan ofthe

force; at thrict: the dillance, wirh

ninlh part ; at fou r·

times the dinance, with a fixtecnth part; and fo on This

too is confirmed by comparing the dinance which the moon

fallslna minute from a right line touchiog her orblt, with

the ditlance th rough whlch hcavy botLes oear tt. "

:Uln

faH io that time; anu alfo

compaTlng the.

1;)

(es

which retaio J upiter's moons io theír orhits,

W:I!'\

,eir

re(peélive ¿.oces from J UFitcr. 'Fhcfe forces · will b.

explained afterwards.

The velocity which bodies oear the e:arth acquire

in defceodiog fre:eIy by the force of

n~'vltv

is pro·

portional

the times of theír dercent. l' or, as the

powcr of gravity does oot confin in .. (i ngle impulfe,

bUl is ahvays opetating in a conllant and uniform man-,

oer, it mutl: produce equal effeé'ts in equal times ; aod

confequently

in a

double or triple time, a double or

triple efFeél; and

(0,

aéling unifo,mly on lhe body.

mull accclerare its motion proponionably to lhe time of ltS

de(cent :

To be

a linio

more p.uticular on this fubj ell, Jet us

(uppofe that a body begins to move with a celerity con·

flantly and gradualJy iocreafing,

(uch a manner, as.

wouJd carry it through

mile

a minute; at the

eod

this (pace it wiJJ .f;lÓlve acquired (uch a degree of celeriry,

as is fufficient lOcarry it tWO miles the ncxt minute,

l ho~

(hould theo rcceive no new impuJ(e from the caufe by

which

ilS

rr.otion had beco 3cce)crated: bUI

lhe

(ame

acctleratjng caufe contioues, it

\ViII

carry the body

mile

farther

on which acccunt, jt will have run lbrough four

miles at the end of twO minutes;. and ,heo it wil! ha\'c

acquired fuch a drgrec! of cclerÍly. as is fuffi cíent

car·

ry it throcgh a double {pace in as much more time, or

eight miles iD two minutes, e:ven though the acceleratinn

force (hould

Ola

up6n il r¡o more. Hut Ihis force rlill

continuing tO operate in íl.n uoiform Olanner, wil1 again,

iD an equal time, produce

equal effell; and

{o,

earrying

a mile furrher, caufe

lO mo"e through five

miles the third minute

for, the ccJerity aJready

~c·

quired , and the celerity

0111

3cquiring. will caeh ha\'c

its complete

dTtét.

li~oce

we Jearn, lhat

the body

fllOuld move one mile lhe firO minute, it would movl!

three the (eeond, (ive the third , fcven lhe fOUll h, nino

lhe fiflh, and (o on in proponion.

And thus it appears, that

th~

fpaces dt(cribed in fue·

ffiV l'

{qual pans

time, by 3n unifurOlly AccelcrateJ

,motion, are alwi\ys as lhe odd numbcrs

J, "

5, 7, 9,

é c.