JiSp PROPAGATION OF SOUND. 



Jerles arc carried on ; but no one Had attempted to p.bfefve, 

 whether the velocity of the found Iranfmitted by the flone dif- 

 Its velocity ap- fered from that of the found (ranfmitted by the air. My ex- 

 Uiat ofVght! ^ periments in the quarries underneath Paris have taught me, 

 that the difference is confiderable ; and when the gallery is 

 fufficiently ftraight, to be able to dilcern the motion of the 

 hammer with the eye, no calculable difference can be per- 

 ceived between the conveyance of the motion to the eye and 

 that of the found to the ear. 

 The differences The diftaqce which the found of the hammer can be con- 

 of thcdirtances yjQy^^ (q the ear varies confiderably with the nature of the 



to which lound •^ . . „ . , r tt • 



is tranfmitted uone and the leparalions or nliures in the mats. Having 



through fol d caufed a man to ftrike with reiterated blows againfl an ifolated 

 mafles remark- n i -i, r n r .y r i • i .1 . • i 



a{,jg^ wall, buiit of common Itone or the fame kind as that in the 



quarries, flind cemented with mortar, the found was tranfmit- 

 ted only thirty paces. Striking in the fame manner on a pa- 

 rapet of hewn ftone raifed on the borders of the Seine, the 

 found was tranfmitted 46 paces. Thefe experiments vver« 

 made in the open air by day, confequently under circumftances 

 lefs favourable to the propagation of found than wheii on the 

 calcareous maffes in the quarries j but the difference between 

 30 and 4^' paces, under the fame circumftances, on maffes 

 differing tonly in the dimenfions of the ftones of which they 

 were formed, is very remarkable. 

 Expenments re- Encouraged by the fuccefs of ray experiments in the quar- 

 peated, j-j^j.^ ^^^ by ^|^^ invitation of Mr. Laplace, 1 attempted to re- 



peat the fame experiments on different fubflances. 

 on timber. gy the tide of the high road that leads from the place de la 



Concorde to Chaillot along the bank of the Seine, on the tione 

 wharf of St. Leir, oppofile the fieam-engine of Gros-Caillou, 

 is placed a railing 210 paces in length, formed of 31 pieces of 

 Conveyed far- timber, feparated by four large pofts. The blow of a hammer 

 ther than in the ^j ^^q extremity of this railing was heard diftin611y at the 

 ^ ' other, though through the air it was audible only 120 paces. 



At the diftance at which both the founds were audible, that 

 through the wood was heard long before the other ; and when, 

 ftanding at the greateft diftance from the place of the blow, I 

 Its vclodty ap- heard only the (bund tranfmitted through the timber, the ve- 

 :C"onightf ^^^ ^^^^^y ^^ ^^^ tranfmiffion was fo great, that it was difficult t© 

 ^iftinguiHi any interval between the perception of the found 

 by the ear, and of the motion ©f the hammer by the eye. 



Having 



