1000000031

Ih! ball o/ a Ih""" /n,lu

dipp!d inlo hol 'Walu, Ih,

jluU

1)" Ihfrlnom,l,r

'Will

jin~

/;11/'

b'fo" il b'gins

lo rifo.

Not ooly

fluid~J

fueh

as fpirits, oil. or mercury, but

Jikewife glars,

or iron, or ..

Imoll any

hard

bodies, will ex·

pand when they are heated, and \ViII

cootnét

agaio when

they

grow cold.

Now, when the ball of a thermometer is

dipp~d

ioto

hOI

water, the heat will be coml'nunicated

the gla{s of which

che

hall is made, before

is cammuni·

cated to the fluid contained in [he ball.

lhis mean$' the

ball \ViII be expanded, and Ihe eapaeily of il will be ioerea–

red, fo ,h., fome of Ih< fl uid wdl Conk OUI of Ihe (lem iOlo

it .

BUI wheo the ball has beco long enough in the water

for the fluid witbio

jI lO

be heated,

thls

fluid will be

expando

ed: and {hen il will rife ioto the Hem, and will coolioue lO

riCe as the

heal ¡ncreares.

SOUND.

S ound, in

Ih~

!Jod.!

/ha/

prodllcu

it ,

Iranh/inK moli,m :

//'ir

11Iclicn

j¡

cOIJJIl1"nica/(d

lo Ih(

air. and

'''~

air

con–

tJ(JI il l o Ih(

~ar.

W HEN

anyelafl ie bo·dyi. flruek .

produce a Cound,

,he body, or fome pa't of it, i5 made to vi brate. This is e–

videot to feofe io the I1ríogs of

violín or harpriehord

for

ei,h« Ihe eye may Cee. O¡ Ihe hand may feel, Ihe trembliog

of Ihe flri ngs, when by flrikiog Ihe", they are made

Couod.

Sc:e

MUStCK.

a bell i. fI,uek by itS c1apper on !he ioCod., Ihe bell i.

made

vibr ..lIe. The baCe of ,he bell i. a eirele; bu, by

llriking aoy

pan

of this eircle on lhe infide, the

part

which

is .l1ruck

will

fly OUt

little way, fo lhat lhe diameter, ·which

paITes lhrough Ihis pan of lhe circular bafe, will becoOlc

longer than aoother diameter which cro{fes this al right

aogles. Therefore by Ihe flroke ,he baCe will be eh.oged

jn,o an ellipCo•• !'IhoCe looger axis will pafs Ihrough Ihe p. rt

:ig.iofl which Ihe e1apper f1ru ek. Hu! lhe c1allteilY of ,he

bell \ViII reflore ,he fi gure of ,he baCe, and \ViII make Ihe

pan which was forced

OUt

of its place return back. This

pan

returning will acquire veJocity, io the COlme manner

ao elallie llriog would io lhe fame cireuOln aoces.

And

fioce

acquires velocity in returoiog tO¡tS place, it wi ll nOI

flop al that placr, bUI

will

over-ruo it. Thus lhe circular

figure of ,he baCe will be ehanged in,o an el'lipr,s agaio ; on '

now lhe lhoner axis will pflf5

t h roug~

the pan lhat was

6rfl flruek.

Ihe bell was

be flruek

6rfl by a hamo

mer

Ihe oUlride. the pan rlruck wouJd move iowards ;

aod fu ch a motion would I.kewife chdnge Ihe bafe ioto

d ilpCos: only io Ihis eafe Ihe Ihorter axis of ,he ellipCo.

would p;.[s throl1gh that

pan

where Ihe blow was gi veo.

The e1 .fllei,y of the

Ir.II

\ViII reflore iu figure ; aod as Ihe

pare whlch was firu ck will acquire veloclty

returniog

t O

prop~ r

ritu:ttioo, the acquired vcJocilYwill

00 1

fuffer

jI 10

reO (liere, 'bUI wilJ carry il fa rther out from lhe oppo·

Ii,e Code: . nd ,he

h.Ce

will by ,hi. meaos be . gaio ehaoged

lotO ao

cllip!i5,

having the looger axis al thar p"rt where lhe

bluw

was ti llt gi \'eo. T hu9 \Ve have feen, thal where·ever

the

hdl

is Hruck. Ihe p1TU or

wi ll pcrform one vibrationj

the

p.ri

. whieh i, Ilruek will yidd ' o ,he blow; Ihe elafli·

el! y ur the bell will bring it back to ils former fil ualioo ;

:-~turníng,

will ~:~qui"e

vdoci,y;

and'<ts

f~ r :!s

tht:

blow

h¡d

driven

one

way, fa far

lhe aClluircd

,"c1ocity

will car-

ry it the other. BUl fin ce, after ooe vibration is thus

per.

formed, Ihe figure of Ihe

b.Ce

wllI be elliplie.l; Ihe pano

of [he bcll will vibrate a {eeond {Ime; and fa

on,

io lhe

Came

maoner (hat ao elaílic Hriog

vd.ratc::s.

The fame flroke which makes a bell vibrate mak" il

round too; aod

lhe vi,brlitions decay,

t~e

(ound grOWI

weaker. Our {eores may coovince us Ihal the parts of

bell are in a trembling or Ylhratory motion

""hilft

lhe bcll

fou nds: for if we Jay our hand upon

jt,

we 1l1ay feel il

jn;

or if fmall ltraws or pieces of paper

a.re

thrown upoo

it,

may Cee ,h a! Ihe jarring or trembling of Ihe beU wiU put

lhem in motioo .

But the air mufl convey this vibratory motion to the ear:

for otherwife. though the founding body is molde tO

vibr.ue

no (ollnd will b«; heard. Thus

a bell

rung in the re–

eeiver of ao air-pump, the fOllnd wiJl grow weaker

,he

air is exhauH'ed; aoJ o when ;dl the air i5 drawn out of the

receive r. no fou nd al all will be heard . When Ihe air

admiued

~gaio

ioto Ihe receiver, the Ii',uhd will al lhe

firll:

entrance of the air begio to be heard, aod will gro\V louder

as more air returos.

the

bell

\Vas to be rung in like man–

ner io a veITeJ where Ihe air is condenfed, lhe found of

would be much louder than il is

commoo air. Aod ac–

eordiogly, when dive" are le, dowo !O aoy grea! deplb of

water, becaufe the air in the diviog-bell i5 much

conden–

fed. ,hey feem

ooe aoo!hor

fpeak mueh louder ,baa

uCua!'

rh, inlenJily o((ou"d, al diffa,nl diflancu

/r."m

Ih, found–

ing body,

in,,:rfoly al Ih, [qua"l

Ih, diflallclI.

Souods may dilFer from one anolher, bo,h in reCpea

their tone, and i.o refpeét: of lheir iotenGty or Clrength .

reCRea of their <one, !hey are dillinguilhed into gra\'e and

acute

in refpeét: of.lheir iotenfi,y, they are difhnguilhed

iOta

loud

Hrong, aod low or weak , The

Ione

of aoy

found depends upoo the time that an impreffion continues,

aod is nOI ahered by the diflaoce of ,he ear from Ihe Coune!–

iog body. BUI Ihe ih,enr"y or (\reogth of any Couod de–

pends upoo the force with which the particles of air, as they

are eoodeofed. Ilfike !be e.r

and Ihis roree is fouod tO be

dilFereo! al 'dilFetent diflanees, fo Ihal a Couod wbieh is

very )oud ir we are oear lhe body that produces ¡t, would

be we ..kef. ir we were farther from

it.

aod our dillaoce ((om

rn.ay

be (o great thal \Ve canoot hear il

,,11 .

The proponioo io which the ioteofity of found decrea·

Ces, as Ihe difl aoee of ,he ear rrom ,be Coundiog body in–

creaCes, is this : If lhe difFerent dillances al which Ihe eal

is placed are to ooe aoother as

1,2,. 3. 4. 5;

theo

'.he

fq UiHes of thoCe ciiOolnces are

4. 9. 16,

and the

10-

leoCo,y of fouod \ViU be iovorCely as ,hefe Cqu.res, or as ,he

reciprocals of thc::Ce

(quares

;

that ¡s, the Clrength

Ihe

fouod will decreafe

lhe (",me proponioo with lhe frdalOnr,

.;. .j.

-ir,

which are the reciprocolls of

l. 4,

.9,

16 . 2

S·

This is what we mean when we

fay.

thu the Inleofiry

fouod is inverfely as the fquares of lhe dittanc(s, or that il

decreafes io lhe depu tUre of the ear (rom lhe foundiog bo–

dy in Ihe Carne proportion Ihallhe fqu.res of Ihe difiaoccs

¡ocreafe,

r hl inlmjily o/ foun d d"r<(lfll al Ih, vibralionJ in lb'

f ?unding hody gro'W 'Wlaler.

ao elafl ie flri og wa.

flop all

once, ,he Cound

~ro·

duced

woul~

eeafe imn:tcdiatcly. Bu! ir Ihe

Vlbrallo~f