On the Production of Sounds in Vapours, 277 



which originate from the brain, and the much greater which 

 branch off in succession from the spine into the adjacent 

 pans ; an arrangement which distributes the source or vita- 

 lity along the whole frame of the animal. 



I am, sir, your most obedient humble servant, 



John Carr. 



Princess Street, Manchester, 

 October 7, 1809. 



XXXIX. Experiments on the Produclio7i of Sozinds in 

 Vapours. By M. Biot. — Read at the Institute, October 

 12, 1807*. 



XNuMBEHLEss experiments have been made by natural 

 philosophers on the production and propagation of sound 

 in diflert^nt mediums : they have demonstrated that it nei- 

 ther iri produced nor propagated in vacunm; they have ex- 

 amined its transmission through Hquid and solid bodies : 

 but no one, to my knowledoe, has repeated chose experi- 

 ments in vapours, and yet this research is well adapted to 

 excite curiosity ; for in discriminating between the facts 

 which experience has disclosed relative to .the constitution 

 of v^ipours which lill a space, and in applying to them 

 mathematical principles, the foundations ot the established 

 laws of the minute vibrations of elastic fluids, it is evident, 

 that absolutely no sound shoidd be produced in them. 



In fact, it is proved by the experiments of Deluc, Sn.us- 

 snre, and Dalton, that the qu;\utity of the vapours of water, 

 or of any other liquid formed in vacuum, depends alone on 

 the dimensions of -the space and on the temperature : in 

 short, if lliis va|)onr has an elastic force, capable of sus- 

 taining the manometer at a certain height, and if it be 

 slowly' compressed, so that it may occupy less space, the 

 elastic force will not increase by this compression, as would 

 happen to a permanent gas ; but part of the vapour will 

 assunie the li()ui(l state, without which the manometer va- 

 ries, and It becomes stationary only as it agrees with the 

 new hmits to which the space is reduced. But the contrary 

 will happen if the space is increased instead of being dimi- 

 nished : afresh quantity of vapour will arise to fill it, with- 

 out producing anv change either in the elastic force or in 

 the manometer. These results are perfecily established by 

 philosophers, whom I shall hereifter quote, and we may 

 with great ease be convinced of their accuracy. For the 



* From Mtmoira ih la Sucuti! d'Arcuvil. 



S 3 purpose 



