PRODUCTION OF SOUND IN VAPOUR. |73 



of the fluid mass, so as to permit sound to be produced and 



transmitted in it. 



Experiments oh the production of sound in vapour there- This may be 



fore are calculated to decide the question, wiiether heat be yfoug^ttothe 



7 , '^^"^ °f experi-. 



really evolved in an aeriform medium by the eifectof the vi- ment. 



brations of sonorous bodies, as we see it in general extri- 

 cated by any rapid compression. Thus we may subject to 

 decisive proof the ingenious idea of Mr. J^aplace, by which 

 he has found means of reconciling the mathematical theory 

 of the transmission of sound iu air with the results of expe- 

 rience, taking into account the heat evolved: for, if the 

 effect he supposes do not take place, the vibrations of sono- 

 rous bodies in vapour should not produce any sound; and, 

 if they do produce sound, it can be only in consequence of 

 the evolution of heat. 



Induced by these motives, I made some experiaients on Sound was 

 the subject, which completely succeeded. I then repeated P^<^^"'^^° '» 

 them in a more perfect manner, in the philosophical apart- 

 ments at Arcueil, with my friend Aniadeus Berthollet. Mr, 

 fjerthol'et, and Mr. Laplace were present at these experi- 

 ments,and themselves verified the facts I am going to relate. 



We took a glass globe that held 36 litres [near 38 wine Apparatus d«^ 

 quarts]. Its orifice was closed by a well made cock, so that ^^"'^^* 

 a vacuum might be made in it, which it preserved with great 

 accuracy. To this cock another could be screwed ; so that, 

 by pouring a liquid into the space between them, and clos- 

 ing both, this portion of liquid could be afterward intro- 

 duced into the globe, without admitting any air from with- 

 out. The sonorous body was a small bell, suspended within 

 the globe by a slender string fastened to the lower cock. 



A vacuurn was first made within the apparatus to the Experiment, 

 greatest nicety, and eyen so as to exhaust a great part of no^oy^^^""' 

 the hygrometrical water, that might have existed in the 

 globe, which however was very dry. ffhen, holding the 

 globe by the copk, we set the bell in motion, so as to satisfy 

 ourselves, that the clapper struck very forcibly against tiie 

 sides : yet, with all the attention we could bei^tow, even 

 close to the globe itself no sound could be perceived ; so 

 that there was no perceptible sound in a vacuum, agreeably 

 to the ejtperirnents of Hawksbee, and all other philosophers. 



We 



