*S Tubes rendered harmonious ly Hydrogen Gai, 



than the volume of the bulb. To determine it, I {luit with 

 my finger the orifice of the tube : at the moment when it 

 began to found, 1 immcrfed the orifice in mercury, removed 

 my finger, and left the apparatus to cool. The vapour be- 

 came CO n den fed ; and I could judge, by the quantity of mer- 

 cury which the preilure of the atmofphcric air made to afcend 

 in the tube, the fpace which the vapour had occupied. 



Such are the four conditions eflcntially neceffary for ob- 

 taining founds : a bulb at the extremity of the tube ; the. 

 prefence of a very fmall quantity of water or mercury in the 

 bulb; the application of a ftrong beat to the bulb while the 

 rcll of the tube remains cold ; and, in the laft place, the 

 Cmultaneous prefence in the apparatus of vapour and atmo- 

 fphcric air. It is not neceffary to add, that the orifice of the 

 tube mu(t alwavs be open. Let us now examine what may 

 be the caufe of the found. I wiflied firft to afcertain whe- 

 tlier any chemical decompofition of the liquid employed took 

 place. For this purpofe I took a tube of fuch a length that 

 the liquid might be entirely condenfed in it. I weighed it 

 carefully before I made the experiment : I then made it emit 

 founds,' and found, after producing this efFeft feveral times, 

 that its weight had neither increalcd nor dccreafed ; whence 

 I concludecT that caloric produces no chemical efftft on the 

 liquid, and that the latter merely undergoes fucccflive eva- 

 poration and condenfation. Is it to this evaporation, then, 

 of the liquid, and its condenfation, that the founds ought to 

 be afcribed ? At firft I believed that this qucftion might be 

 anfwered in the affirmalivc ; but the following confidcraiions 

 made me change my opinion : I firft obfcrvcd that there 

 might be a fucceffive evaporation and condenfation, without 

 the tube emitting any found, on applying to the bulb a fufii- 

 cient heat, but Icfs intenfe than that neceffary for making 

 the tube found. Secondly, in making the experiment with 

 a drop of water, I confiantly found that the moment when the 

 apparatus began to enter into aftiun was that when the whole 

 of the water was evaporated, and, confequently, when the 

 heat aclcd on the vapour : if a fingle atom of liquid remained 

 in the bulb, the tube' was mute. From this fact I conclude 

 that the found is produced by the a6lion of the caloric on 

 the vapour, and the readlioii of the latter on the alinofpheric 

 air. The following is the manner in which I conceive that 

 this phsenomenon takes place : The vapour contained in the 

 bulb receives, by an addition of caloric conveyed to it from 

 every part in a large quantity, an inereafe of volume and of 

 tlafticity ; it proceeds with force from the bulb to the tube, 

 and expels the air contained in it j but this air and the fides 



of 



