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of 'Re Ilriag de..y gradu.Jly, ,he found will likewife keep
gtowing weakcr, 1111 il bccomc:s toO we..k 10 be: he,u d.
Thc Hnng pcrforms 2011 ItS vibrauo:ls flOm the fidt lO .he
Jan in cqu.d umes, and conrc:qucntly et;\ch pulle that Ihe
firmg produces 15 ploducetJ In .lO el)'l..ioll time, <tno UptlO Ihat
aceou",' oach pul(o (,om ,he 6r11 ' o ,he laU \V,JI have ,he
fa me tilicknels HUI wh~n Ihe of the: pull..: 15 g"
ven, ~he quantity al' ¡ir, or number of pa.nleles. by vJhll.:.h
the car is Itruck. will likewlfe be' glven; and Ihe moment
with whlch t[ 15 Hruck, Of l he intenfity of lhe: found, wdl
be as Ihe . docity wuh which Ihe panicles move. Now lhe
,c:locity of Ihe Hnng is CuccelIivdy communlc;ued to {he
particles of air, as lhey are la Vlbr¡He. Therefore,
as {he velocity of Ihe (trlng dec<lys, Ihe velocuy of Ihe pu·
,icles, .nd confequeotly eho InteoG,y of ,be found, wiU Itke·
wife decal.
Th, inlM.JilJ of fou nd N incrNlftd b) a fplaling.lrump<l.
When a rilan (peaks withOUl r,,!ch a [IUmpet, the pwJ r~$,
as lhey are produced, themtelves in ;t l! dlr.ettlons , or
the mOlioo is immedloltely commuOIcated [Olhe alr .dl round
him But ir he fpe"ks 10 a t rumpel, 1115 '1DlCe, that I~, ,he
motian producc!d by h ls voice, 1$ confined (O (he por–
tion of air containcd 10 [he (rUmpeL Far ,hls rearon, as
there ..re fewer parllcles la be moved tban (here are when
the morian dilates itfelf immedi.uely in all d¡redlons . lhe
motian that is comnlunicated \Vdl be grcoiler, 3.0d conre–
quently, when lhe voice comes out of lhe lrumpet. in In–
ten(jl\- or Clrength will be greatc:r. than il would have beco
ir i, had beeo p,opaga,ed in all d".tllOn. al ,irllo
Sound mOfJeJ 'W;lh Ih~ fa"u "doeil) at illl diJla"cufrom
11:, ¡oundiflg bodJ.
The found of a cannon, or of a bell, moves at the nle of
114 1 (eei ;n a fecond a, all d,nance, f,om ,he gun o, ,he bel!.
H it moves at dlls rate for {he 6rCl mile, it would mov~ j\J1t al
the fame rate for lhe (eeond mlk : fo tlU{ a perron who i\
within one mile of {he canno~ when,il is dlfcharged, will
hear {he repor, juft as {oon again as anorher who 15 al the
difiance of two mile5 . The velocily 'of the found doe5 nOI
decreitCe as ít is propagaled forwar ds, hut conunues lhe
f~me (rom ,he fidl ' o ,he lan. Thi, property o( fouod h..
beeo proved by repealt'd experiments.
When foundj/rilu og,inj/ an olllac!e, iJ ,,,,;11 . , r<jl<f/d.
By found we here me~ f\ the pulres in the air, which are"
p,opcrly fpeaking, ,he caufe, of (úllnd. If ,hefe pulles in
their progrefs J1nke upon any obJl ¿c1e, Cuch as a rack, a
thick wood, or lhe fide of a builJing, the :..i r. which is con·
denfed a' ,he oblldcle, is 'preven,ed f,om ey.pand,ng i,fel(
(o,w;"d" o, (,om r,opar.,,,ng ,he found h. y,)nd lhe oblla·
ele. T herefore, in tx?~ndíng urdf,. lhe motlon, whlch would
otherwlCe have becn propag:ued forwards , wilJ bt rCl urocd
from lhe ob!tacle j and a perron, who 15 pl.lced fo as to re–
ceive th~ pulfes io their relu rn , wilJ heu lht: (ouno by r'!·
flcélion Such a reHetled found ;5 c...llt:d an echo.
T he numbt r of fyllAbles which <ln echo n: pc!AlS dillinét·
Jy depends IInon the diltance of lhe obfl"cle frolO whence
,he (ound i, ,cfl etlcd, T lie fyllab les ,ha! wc he", dl/lillo!!.
Jy I'epcafcd ue thofe which are returnc..i a(ler we h..."c
done fpeaking . There(orc:. i ( the oulbdc 15 fo neH fO I'!',
that the fidt f)'JlJblc we fpe::k wiJl be rClurnt:d before \Ve
caD fpeak a fcconi, 00 reBeClcu founu al ..11 " O be h~ard
A T e s.
dillintlly; !¡ecdll(e ,he di' eét and rrOdled focnri, Or ,he
vOlee: ami lhe echo. wi ll be confoundC"d with one anolher,
1, ,he oblta. le lS al (uch a d, , ,h., fi ve fyllables m.y
~e Ipokt n bc:(ore one wlll be rt'tu rned; tht n d \Ve fpeak
a {entence conf.{J¡ng of 'en Iyll,bl••, ,he fi,n 6.. wdl be
, efl<tted whillt v,e a'e (pe.k,ng ,he "Ve lan, (o ,ha, iD
(p<.kiog ,he live lan (yll.bles, ,he vo'ce will be conrounded
wlth (he echo of the ti ve 5rH. and we Oull h'!2.r Ihe echo of
only ,he 6ve 1.1 fyU.ble. ~,nintlly, b.callre ,liere only will
be returnc:d aftcr we have done fpeaking. But ir the oh·
(Jacle lS d' luch • diCl. nce, ,hat we may fpe>k~en (yll.ble.
before ,he .dt o( ,hem wdl mllrn ,o.,he fpeake, ; ,hen if
wc (p~ak A (entence of only ..n (yUables, we 0,,11ha<edone
fpeaktng before the echo ~egins, and confequendy we may
be., "le wbole lentence diJlintlly repealed by , he echo.
Somefiine5 che: Came found is freqllently repealcd byan
echo. TJlIshappens when there are feverod obO:¡¡cles al dtr·
ferent diUances. For though there are fe ver.. 1obnacles,
ye, ,( alt o( ,he"" are a' ,he (.me dinanc<, ,he foun,d will
be returned from Ihemall al one and, the fame lime; and
con(equently ,ho f...,,1 reBetled founds will be h ,oge·
gc,he" aod wdl make bu, one echo. Bu, if ,he obn.clel
~re al dlff"l.rent dlJ1aoces, each will return the found at a dif·
{erent time, alld as many eehoes will be heard as lherc are
obtlacle. ,ha, produce ,hem:
The D'VING BOLL .
TH E ai, in a diving.bell i. co",prelfed by ,he weigh' of
the atl110fphere before the bell 15 let lio\on into íhe wa.ter.
Bu, when lt J¡a. funk 35 fee, below ,he furface, ,h e ai, con–
talned io ir is comprefied by the wC:lght of the aunofphcre
as before, and by lhe we'tiht of 35 (eel of waler befides.
which 15 t,quiv"lcnt tO aoother a(mofphere. Therefore the
compreffing fo,ce a' ,hi. dep'h is doubled, and confequen'–
Jy rhe ai r in Ihe bell wllI then be tWlce as denfe as Ihe com·
mon air that we brea.rhe . As much ai r, likewife, as jull:
6115 lhe btll, when it is ar the {urf¿ce of _he w.uer, will, at
,he dep'h of 35 re<t,. oqly fill hdl f of i, : fo, as ,he como
p,tffing fo ,ce is doubled, ,he f, me qu. n'lty of air ...iU be
reduced 10 half ItS ufu ..) diOlenfions. For Ihis reaJon, the
Water would "fe into che bell , through ,the b..fe or bOtlOOl
of i" w"ich is allVay' open, aod would fill ,he o,her half
of it, if there w...s nOl a contriv,¡nce for bnnging down ad~
ditional atr enough 10 force OUt \his \Vater, and tO keep {he
whole cap<tcity 01 [he_~ell fu ll of ai ro ' H oweTCr, ~he ;:Iir
wlllch fiJls il wdl, at tht depth of ~ 5 (eet, have l""tce the
denGIY Ih:u comnlOn .ur has; ilnd ;\1 1he depth of 10 (eet,
whcre il walJ be comprerfed by lhe weight of anolh . r aunQ–
[phI re, it wilJ h.l\'c te IpIe the denfity 01 cornmon air.
\Ve {hall hac: gi ve a (hon ¡ccoune of the conlrinnct foc
bringing down.,..addition<tl ai r tO the diving.bell : becAufe it
wtlllerve \0 (he\V, [hat if a vefl'eJ rull of ;tlr IS fUltk i!llo wa.–
Ter, and (he Water cornmunlCates wilh the air in ,he v~l1el,
then lhe pre(fure uron thac air will he fo much Areat'er
as lhe vdfd .is funk fa nher belo\V the furf3ce of the w"ter.
The COnfflVanr.e IS Ih.5. A barrel is mide ufe of, which
has one bung-hole in lhe lower put of it. and another in
the UPPt.'f pan . A leathern pipe is (¡ (tened tO Ihe hole iD
the upper part; and thls pipe is fo long. ChAl, when it hans~
J nwn on llit: oUlfide of che b:trrel, its bnfi ce rt!aches below
,he bung, hole in ,he lower part. H ,his b, rre!. ~y ,h:
hclp (If weights fA(b.:ned 10 it, is made to (ink with in bot~
100) downwa,ds, ,lte waler, by prenillg ag.inlt ,he lower
bu¡;~..:.