1000000031

towards the 'beginning of the fcale MN, over

whic~

the

l'0int of chal

index ..

moves.

This

fCtlJe is

divided

into

inches and tenlh parts of

¡neh: lhe

firn,inch

is ruark·

1.000.

the recond

:2000,

and fa on. A

bar

of metal

laid imo

DOlches

lhe

top of rhe ll11ds

and

o ;

one end of lhe bar bcaring againH rhe adju Hing fcrew P,

and [he other end againH

lhe

crooked ¡ndex El,

2~(h

part of its

Icngth ffom its centre of motiao F .–

N o..u ir is plain. that however much the bar O Icngthens,

ir will move that

pJ.rt

of lhe ¡ndex E l againfi which it

be:lI s jurl as far: bUl rhe crooked cnd of lhe fame index,

'ncar

heiog

times as far from lhe centre of motiao

:f'

as lhe poinl is againO:

which

lhe

bar bears,

will

mave

.20

times as (ar as the bar lengtheos.

Aod as this

crook~

end be.., againft ,he index

GK a,

ooly

20,h pare of

-its \Vltole Icnglh

from ¡ts centre of motioo

t"'e

'poiot S will ruo{'e through 20 times the fpace that the

point of bearing near H docs..., H enee, as 20

muhipli~d

:!o

produces 400, it is e"idenl, that if the :rr lengthens

but a 400th part of

¡neh, the peine

S ill

move a

whole ¡oeh

DO ,

the fcaJe; and as e\'eey ine is divided

be pu, in,o ,he ¡'<ale

,he olher enJ as \Vil! eicaé\ly

counterbalancc the auraélioo, chen, if the iron be brought

twice as near lhe Clooe as berore, that ¡s, ooly t Y':O (eolh·

parts of an ¡neh from it. there mue! be fou r time!: a9

{Oany grtlios

pUl

into the

f~ale

as before,

arder

a juH counrcrbaJance to the auraélive force, or tO hinder

th e fiane froln dercending and adhc:riog to lhe iron. So

four

gr~ins

wilJ do in the forrner cafe there mull be

fixteen i.o the lau er. But from Come later experiments,

made with che greatell accuracy, lt is fOllnd that the (orce

o( magn.etirm decreates io a ratio betweeo the reciprocal

of ,he fquare and ,ho reciprocal of ,he cube of ,he dif–

<aoce; approaching to the one or the other, as the mag–

nitudes of the ;¡tt raéling bodies are varied

Severdl bodies, panlcularlyamber, glaCs. jet, fcaling–

w~x,

agate. aod almon all preciom; Hones, have a pc::cu..

liar property of attr.é\ing

and

repelling ligh, bodies wheD

heated ,uy ,ubl>ing. This is c;¡!led

~/r.{b'ical

allraflíon;

for lhe properties of which. fee

E LE CTRJCITY.

Of Central

r oras.

into

eq\lal pans, if lhe bar lengthens bUl lhe lotb .

'VE

h!\l"e already mentioned it ...

s a

oeeeffary confe..

pan of the 400lh part of aD ioeh, '-'ieh

¡,

ooly the

'~lueoCdlll&ri(ji'lg

from lhe dcadners or i02.élivity of matter.

4000 rh

part

of ao inr.h,

lhe

point

S will

move the tenth lhat

,,11

bodles endeaVOtH

eontinue

the (tate they are

p are of an inch, which is very percep,ible.

in, \Vhe,her of rell or mo,ioo .

,he body

(6g

6.)

T o find how much

bar leng(hens by heat, firll

lay

u'ere pJaced

any pan of free Jpace, where aothiog ei ..

it cold ioto lhe notches of ...the fillds, aod turn the adjufl. ther draws or impels

aoy way, it would for ever remain

¡ng (crew

until the rpring

brings the point

of the in

l b.u

p:Ht

{pace, becaufe

could have

tendency

¡ndex

to the beginning of the divifioos of the rcale 2.t of ¡trelf

remove any way from lhence. I f it receives

theo, Wilhout ahering the rcrew any fanher. take off

fingle impulfe any

way, as

fuppofe from

towards

che bar, and

Tub

it with a dry \VooJlen cJoth tiJl

feels

will go on io that direélion ; for, of ¡trelf it could De–

-warm: and \hen, laying it on where it was, obferve haw vu fwerve from a right lioe, nor flop its courfc.--:-Wheo

far it puChes the point

upon.rhe rcale by means of the it has gane through the fpace

AB,

and met with

re–

crooked index

El; and

the poim

S \ViII

fhew exaétly lillance,

ilS

velocity

\Viii

be the rame at

WOlS

how much the bar has Icogthened by the heat of rubbing. and 'this velacily,

,il}

as rnueh more time,

wiII

carry

lhe bar cools, the rpring

bearing againn the ¡ndex through as much more {pace, from

e ;

and ro on

KG,

will

caufe ilS paiol S to move gradutlIly baek to· for e\'er. Therefore,

whto we

fee

body in motloo;

wards

the {cah:: and when the ba r

quite cold, \Ve conclude that fome other fll bfiance muU have

givcn

the iodex wiH re{l al

1\1,

where tt \Vas before the bar was it thac mOl ion ; and when we lee a body fall from

roo–

made warm by rubbing. The indexes have fmall rollers tior. tO ren, we condude that rome other body or caufe

\loder thcm

aod

wbich, by turning round on Ihe flopl it.

fmooth wood as the indexes move, make their motioos

As all motion is naturalIy reélilineal, it appears,

that

,the eafier, by ukiog

afta

greilt pan oflhe (rillioll, which

bullet projetú:d by tht.. haod. or Ibot

from

a cannon,

\Vould .othcrwife be on the

píos

aod

aod of the points would for ever continue

move

the

me direét!oo

the indexes

them~ehes

the wood.

received at I1rH, if

other power di\ erted

eourre.

Berides lhe aniverral propenies above mentioned, there Therefore. wh(o we fee a body move

a curve of any

.are bodies which ha\'e properties peculiar to theOlrelves: kind \Vhatever, we conclude it mua be a(led upon by

1""'0

fuch as the

I,,~dnooe,

in which the mon remarkable

are

powers at lean, one putting it io motion , and anlJ: her

thefe.

atlraéls iron aod fleel only,

2 .

confiaody drawiog it off from the reéliJrneaJ et urfe it would other..

turns one of ils

fides

the north and aoOtheT

lhe rOUlh, wire have continued to O1o\'e in: and whenever that

when fufpended

a thr«d Ihat does

001

twin.

3. h

power, which benr the motion of lhe b'ldy f!Vm

{}raigJ.1t

communícatcs all its propenies to

piece of {leel when line into a curve. ceafl!s to aél,

lhe

body wll1 agaio move

rubherl upon

it,

withollt [o(ing any itfelf.

on in a !h ilight linc,

touch~og

tltat point of (he curve in

Aceordin~

H elOlam's experiments, lhe ;¡tlraétion which it was when the aétion of that power ceaCed. For

of ,he .Ioa¿ffonc decreafes as .he f'luare of the di!lance example, a pebuJe moved rouod in

fl lng ever

long

iuneares. Thus, if

loadllone be fufprnded at one end time, will

fl y

off

,he

moment i( is fe l at Jiberty by fli p..

bCllance, ano cOlJlltcrpoifed by weights al the other

pirig

one end of

tia

{}jog cord; and

wiJl

roo on in

line

end,

t\'1d

flott piece of iron be plaeed beoeath it, at the touching ,he circle it delcribt d befare

which

line

\Vould

drflance of (ou r temhs of 3n io' h, the none will ¡mmedi· ,aélually be a (haight onc, if lhe canh 's attr"e.ion did nut

-'tely ot-fcer,(1 ar.u acihere

tCl

lhe iron. But ir the llone aiT(B Ihe p(bble, ?od bring it down to lhe r.rour.d.

b e "gain removed lO ,he fame <tinaDCe, .nd as

many

graiDs This

n.o\\'"

lhal ,he'na,uralt<ndency

,he

p<bble,

whcn

PUt