168 M. V. Regnault on the Velocity of the 



est wave, the velocity which I call the minimum velocity (vitesse 

 minima) . This determination could only be made with any pre- 

 cision in the wide tubes of 1*10 metre diameter. It was found 

 that 



W = 330-30, 



a value which differs very little from the mean limiting velocity. 

 In tubes of smaller diameter the minimum velocity is still less. 



III. When the wave is produced, not by the sudden explosion 

 of a detonating mixture, but by the injection of a small quantity 

 of air more or less compressed, its' velocity of propagation in the 

 same tube is greater when the intensity is greater ; so that the 

 velocity of such a wave, like that caused by the discharge of a 

 pistol, diminishes continually. 



In the tube of 1*10 diameter the waves produced by the injec- 

 tion of compressed air have sensibly the same initial velocity of 

 propagation as those caused by the discharge of the pistol; but 

 their mean limiting velocity is a little less. The same fact ap- 

 peared in a tube of 0'30 metre diameter when the excess of the 

 pressure of the injected air was sufficiently great. 



IV. The behaviour is the same of the wave produced by the 

 sudden closing of the orifice on striking it with a disk moving at 

 a great rate. The velocity of propagation diminishes sensibly ac- 

 cording as the path increases. This is shown very clearly by ex- 

 periments made by means of a piston impinging upon a tube 

 0-216 metre diameter (la route Choisy-le-Roi). In the great 

 tube of 1*10 diameter which forms the service-pipe of Ville- 

 monble, the mean rate of propagation, in the same path of 9773*5 

 metres, was found to be 



y' =333*ll metres when the sound is produced by a pistol. 

 V — 332*56 „ „ an impinging piston. 



So that the wave caused by the piston travels a little slower 

 than that caused by the discharge of a pistol ; but this is entirely 

 due to the less intensity of the former. The wave caused by the 

 piston never gave any indication on the membrane of a second 

 return which would correspond to a distance traversed of 19547 

 metres, while the wave caused by the pistol never failed to indi- 

 cate frequent returns. 



V. The experiments which I have made upon the waves pro- 

 duced by the human voice and by wind instruments are described 

 in detail in my Memoir : the description of them would be too 

 long for this extract. 



VI. Our theoretical formula? of the velocity of sound in air do 

 not take into account the barometric pressure to which the air is 

 subjected. If these formulae are exact, it would follow that the 

 velocity of a wave in a gas is the same ivhatever be the pressure to 



