1000000031

e s.

Eut while

gr:tvity

exifis, (here

no occa{ion for fuch

JO.

As rhe

centrirugal

force of (he light

body

B wjH

vortcxcs; and ",hen

ccares to exifl, a llone

thrown

nal

allow

lhe

heavy body A

remain

in lhe

centre

upwan:.s

\\ill

never return

la lhe carril

agaio.

motion, even

(l1ough

be 24

times

as heavy

B; let

body be (o placed upoo the whirliog

bo.rd

of us oo\v t;¡ke the ball A (fig 7.) which weighs 60uoce"

the machine

(fig.

1.)

that [he centre of

gravily

of lhe and

conoea

lhe wire

\Vlth lhe b..1I

1:1,

which weighs

body be di retlly over

lhe

centre of

lhe!

board, and the ooly

Dne

ounee; and Jet

lhe

fork E be fixed inro

lhe

centre

board be

pUl

ioto ever fa rapid a motion

lhe

wioch B. of lhe whirling-board; lhen, hane. lhe balls upan lhe fork

the body

\ViII

turn round with lhe board, bUl \ViII not by the wire

(ueh

a manoer thac they; may exaétly ba·

rcmove from the middle of

il:

for, as all parts of the lance each other"; which will be when {he centre of gra·

body are in

t'quilih,-ilJ

round its centre of gravity, and vity between thern

in lhe wire at

is fupparced by the

the cenrre of gravity is

reJl in the centre of mOtiOD, fork . And this centre of gravily is as much nearer to

the .centrifugal force of all pans of the body will be e· the ceotre of the ball

thao lO the centre of the b.1I

qua) al equal d¡llances rrom ¡tS centre of motion; and as -A is he:avíer than B, allowi ng fur the: weight of the

therefore the body \Viii remaio in its pl2ce. But ir the wire on each Cacle of the fork. 'I'his done, let the ma·

centre of gravity be placed ! ver (o litde out of the CeDtre chine be put into motion by lhe winch; and lhe balJs A

o f mofion. and the: machine be turoed fwiftly round, the and B \ViII go round their common centre of gr;¡vity

ti,

body \ViII

off towards lhat ride of the board on which keeping their balance, becaufe eilher will not allow the

·¡ts ceotre

grl.ity lies. T hus, if the \Vire

(fig

S.)

oth'er lO

off witb it. For. (uppofiog the ball

with ils liu le Dall B be taken

a\~ay

from the demi·globe only one ounce in weight, and the ball A to be

ux:

aun·

A , aod the flat fiJe

of this demi globe be laid upoo the ces; theo. if the \Vire

\Vere equally heavy 00 each

\IIhí rl ing-board of lhe machine, fo as their centres may lide of the fork, the centre of gra-vity

would be

cúiocid:;

then Ihe'board be tucoed ever (o quick

times as rar (rom rhe centre of the ball B as (rom tbe

lhe wínch, the

demi

globe will remain where it \Vas

pta.

centre of the baH A, and confequently B

wiII

revolve

cedo But

[he \Vire

be fcrewed in the deroi-glohe at wirh a velocity- fix times as great as A 00C5; which will

[he whole becomes one body, whofe centre of gravity give B fix times as much centrifugal force as any fingle

is no\V at or near

Let the pin

be fixcd in the centre ounce of A has: but then, as B is only one ounce, and

the whirliog.board, .od the deep groove

cut io the

fix ounccs, the whole centrifugal force of A will exaélly

!la<

fide of the demi.globe be put upoo the pio. (o as the bal.oce the whole ceotrifugal force of

aod therefore,

pio m.y he in the ceotre of

[See

fig.

6. where this groove eaeh body will deuio the other (o

tO make it keep io it.

is repreCented

and let the whirling bocrrd be lurned cicele.

T hís

fhews tl).at the Cun ilnd planets mull all move

by tbe wioch, wlllch will carry the liule ball

(fig

S.)

rouod the commoo ceotre ofgravityofthe whole fyllem•.

with its wire

and the demi.globe

A. •11

round the io order to preferve that jull balaoce which takes place

centre pio

ci;

-;¡nd then the centrifugal fOTce of the Jiule among them_ Far, the planen being as unalt:ive and

baU B, which weighs ooly one ounee, wilJ be fO/great,

d~.ad

as tbe above balls, (hey could no more have put

as to draw off tRe demi.globe A, which weighs two themfelves into motion than (befe balls can ;

Dar

havc

pouDds, until

t.be

cod of the groove at

firikes againO: the kept in their orbits, without being balanced at firlt wítn

pin

and fo prevena (he demi globe A from going any the greateO: degree of exaétners upon their common centre

farther; olherwife, the centrifug.1 force of

would of gravity by the Almigbty

a.od

that

m.de

them

aod

have been great enough lO have carried A quite off the put them iD motian.

whirling-board. Which Ihews, that if tbe fuo were

Perhaps it may be

here

a./ked, that Goce the centre of

placed io the very ceotre of the. orbits of the pl. o"., it gravitybetweeo thefe b. lIs mull be (uppon ed by the fork

could not pollibly remaio there; for the centrifuga! for- in this experimenl, what prop it is that fupports the cen.

ce, of the plaoets \Vould carry them quite off, aod tbe u e of gravity of the (olar

(~lIem,

.aod coofequeotly be",.

fuo with them ; e(pecially wheo (everal of them happeo. the weight of all the bodies io ¡t; . od by what is the

ed lO be ¡o aoy ooe quuler of the heaveos. For the fuo prop ¡tlelf (upported

The .o(wer is ea(y aod

pl.io

; for

and p!anets '

3.re

as much conneéted by the mutual attrac· the centre of gravity of our balls mult

fupponed, he–

tion that fubfiUs between lhem, as the bodies A and B caufe they gravit:ue towards the.eanh, and would there.

are by the wi.e

which is fixed tO them both. And

fare

faH tO it: but as the (un and pI ¡oets gravitate only

( ven ir there were bUl one ringle planet io the whole hea- towards one another, they llave nothing elfe tO (aJl to ;

vens to go (ound ever (o Jarge a fun io the centre of its and thererore have no occ.dion for any thing to {iIPPOrt

orbit, its centrifugal force would foon carry off both it- their commOD centre of gra\'ity: ilod if they did not

felf and lhe fun, For, the grealdl: body placed in any- move round [hat centre, aod confequently acquire a ten–

part of free fpace could be eafily moved: becaufe if there dency to fly of froOl it by their mOlioos. rncir mutual

\Vere no other body to atlraét it, it could

have

no weight attratlions would foon bring tnem tugtther; and fo the

Or g ravity or ¡lfdf; and cOllfequendy, though it could whole ",ould become ooe mars in {he ruo: which would

have no tendency of i1felf lO remove from thu pan of alfo be the cafe

the1r velocities rou:1d lhe fun were not

{pace, yet it might be \'ery eafily byaoy olher fubflahce. qUlck enough

creclle a cemrifugaJ force equal to the

And perhaps it was this conGderation which made lhe fun's attraétion.

celehrated

ARCHHtED ES

f;ty,

that

he had a proper

But arter all lhis nice adjullment, it appe;¡rs evident.

place at fome dinance from lhe eanh whereon tO fix his ·that the D eity cannot withdnw

his

regulating hand froln

·machioery, he could mo•• the whole ..rth .

his works, .od leare tl:em to be folely ¡¡overoed by the

v.o~.

Ul . N°

70 .

la,,"s