844 iji;li,ktin «k tjik 



INVIiBTIUATlONS IN ACOUSTICS. 



T)iiriii<f llu! IiikI, (|imrlcr of a ccMtiiry, nmnw^ llin timiiy inloroRts 

 wliicli (lciiiiiii(l(r(l mill nigii^cd IiIh iilUMilioii, I iciiry Kliidit il with 

 miicli euro viirioiiM iilniiomciia of ncouHlicH, and added iniicli to 

 our pracliral an well »h tlicor(!ti<;ttI kiiowlcdj^o of lliis imporluiit 

 iiislruiMCiifiilily. In ]H')|, lio nuid a commiinicalion Ixiforo the 

 A nicriciin AsHociaf ion, " On ilio jyimil. of l*crc('|)l il)ility of a direct 

 mid ridlectod Honnd," in whielt ho j^avo M tlio roKiiIt, of e\|>(ii- 

 iiirntftl oliKcrviil ionK, (lio Kid)jectiv(! fiiet thnt a widl or other r(tlleet- 

 inj; Hiirfaco if lieyond tlic; distanco (d' alioiit .'JTi fot from tlic cur, 

 or from tlio origin of tlio sound, givc.H a (liKtingnishal)lo echo from 

 tho Bound ; luit tliiit if tlio ear or tlio Bonnding agent I)0 iiliiccd 

 within thin diKliince, th(i rellcclcd Koiind appcarK to Ideml (rom- 

 pl(!((dy with tlie original oik;. I''rom a iinnil)er of cxperiinentK, lio 

 found thitt ninl< i- tho nanio circiunKtaneoH, tliiB limit of ])erc('pli- 

 liility did not, vmy nmre tlniii a ninglo foot; Imt thnt under dilVer- 

 ing conditioiiH tlio limit of distance ranged from UU to K) foot, 

 (o(piival«fit to ft dilToronco of from (JO to HO foot of Bound travol,) 

 depending partly on tho KluirpncKH or clearnosH of tho Bound, and 

 j)artly on tlio pitch or tlio length of tlii! HoniforoiiH wave, which 

 all'irctod tho nniomit of overlapping of tho two KcrioH. TheHO re- 

 MiltB im|)ly (I dnniiiiMi of ncouBlio improBHion on tho oar of nlioui 

 oiio-Hixteenlli <d' a second; serving to show that \(', viliralionH to 

 tho BOC'iMid must lio alioiit I ho lower limit of a recogni/.uMe musi- 

 cal tone* Ah applied to looturc-rooinB, ho pointed out, tlmi iln- 

 ceiling hlioul'i not \u' inori! than oKoiit thirty feet high, within which 

 elevation, a smooth coiling would tend to re-inforco tho sound of 

 a s|»oakor's voice f 



Many oxperimentu wore afterward made on Iho roKonanro of dif- 

 ferent nmt.erials, hy nieauH of tuning I'lirlis. While a tuning fork 

 suHjieiidid hy a lino thread <M)nliiiued to vil)riite for ujiward of jour 

 ininntoH with Bciircoly any npprooiahlo Bouinl, if placed in contact 

 wilh tho lop of a |iino lidile, Iho sanio vihration continuei] hut 

 ton Bcconds, hut gavo a loud full tone. On a marhle topped 

 table tho Bound wan much more feeble, and the vibration conlinuod 

 nearly two niinntoH. While tho tiiiiing fork against a Ijrick wall 

 gavo a feebin lone continuing for KS secondK, against a lath and 

 plaster partition it gave a sound considerably louder but continu- 



* Tliirt doort iidt i«oi>ni io nf^rct* with remiltH elilfilneil l.y Sfivart Borne 

 twenty yofiiK jhi-vIoubI y ; who (loiuiliiiltid from olinni vnlioiiH with ll»i» siron, 

 " Ihul hdhiiiIk ftio iliKlinnlly |MT('i<|>til)lo, niiil ov«'ii Mlroii« wlioii (!onip(»Hed 

 of no inont limn t-iglil vibialiouM in jiboooikI." (/uu, Knctjil. July, 1H32. 

 Quolwd in Hill. Am. Jour, Sei. for 1832, vol. xxil. p. 374.) ' ThlH latter do- 

 torniiiiiition Ih Buniowloit (linirnlt to ni'onciht with oritinnry ohMxrvntioiiB, 

 n« ll irt (Mrl/iln lliiil intciviilM of onr ciglilli of a Kccon I woviht glvo (i vcr/ 

 fi|>|iii<i'ifili|« r/illlo to nlnio^l ovcry cftr. 



I /'iiirrnl. Am. AiiiKtc. Clnoinufttl, May, 18.'1, pp. 42, 43. 



118 



