132 FROPAGATIO^ OF SOUND, 



Probable caufe While obferving the propagation of found In the galleries, 

 MMrimenu '^^'^ ^ ^^^ feveral times occafion to remark, that a found at a great 

 diftance was frequently repeated, either by reflexion or by the 

 vibration of the walls, fo as to cauie two differerent founds to 

 be heard and diftinguithed, which reached the ear in fuccelfion. 

 As it was poffible that the difference which appeared to Mr. 

 Gay and me might have been produced by the caufe here men- 

 tioned, I determined to repeat the experiment in the open 

 air. 

 The experiment For this purpofe I took two glafs bells, the tones of which 

 opcn^?."^ ^^""^ ^^ ^" o6lave and a fifth, that is, the ratio of their vibra- 



tion was as 1 to 3. A hammer was fo adjufted as to ftrike 

 both the bells at once, and make them found at the fame in- 

 ftant. Carrying this inftrument into the fields, I endeavoured 

 to afcertain whether the two founds reached the ear in unequal 

 times. Several experiments repeated in various places, made 

 me believe a long time, that their velocity was unequal ; but 

 having obferved, that on fome occafions the founds reached the 

 The double ear at the fame time, I was led to remark, that whenever I 

 e° en here by ^an ''"^g^"^^ I diftinguiflied a difference of velocity, this difter- 

 ccho. ence liad been occafioned by a repetition of the found, and 



that frequently very trifiing obfiacles, as trees or hedges, were 

 Grave and acute fufficient to produce this repetition. I repeated my experi- 

 iame velocity, "^^nts therefore anew in the midfl: of plains of greater or lefs 

 extent, as thofe of Montronge, Grenelle, St. Denis, &c. and 

 whenever I was remote from any obftacle capable of producing 

 a repetition, both founds were heard at the fame time. With 

 my inftrument I could diflinguifli the found of the two bells at 

 the diftance of 700 paces or 631 yards; whence it follows,, 

 that both experiment and theory concur to demonftrate, that 

 grave and acute founds have the fame velocity. 

 Cwidufions from from the experiments related in this paper it follows: I ft, 

 the experiments, that the velocity of found differs according to the medium by 

 which it is propagated: 2dly, that this velocity is much more 

 confiderable, when it is propagated by folid and very denfe 

 bodies, than when by aeriform bodies, and of little denfity : 

 3dly, that both grave and acute founds have the fame velocity; 

 a refult to which theory led us. 



A-Ttcry 



