Propagation of Waves in Gaseous Media. 163 



necessary to be traversed for the explosion to become inaudible. 

 I have further endeavoured to measure the much longer path, 

 at the end of which the inaudible wave ceases to give any indi- 

 cation upon the most sensitive membranes* which I have used.y ' 

 I have thus found that : — 



(1) In a gas-pipe at Ivry, having the internal diameter of 0*108 

 metre, the explosion is heard at the other end at a distance of 

 566-7 metres, but the sound is very faint. If the further ex- 

 tremity be hermetically closed with a piece of sheet iron, and if 

 the ear be placed at the end where the pistol was discharged, it 

 requires the utmost attention to catch the sound of the return 

 wave. So that in a straight cylindrical tube of 0*108 metre in- 

 ternal diameter a length of 1150 metres is sufficient to extin- 

 guish entirely the sound produced by the discharge of a pistol 

 containing one gramme of powder. 



(2) In a gas-pipe in the Rue milit aire, 0"30 metre in diameter, 

 the discharge of the pistol is heard very clearly at the other end 

 at a distance of 1905 metres. If this end be closed by a sheet of 

 iron and the ear be applied to the end where the discharge takes 

 place, the reflected wave is indeed heard, but with extreme diffi- 

 culty. In this case the wave has traversed in the pipe a distance 

 of 3810 metres. 



(3) In the great pipe of the St. Michel sewerf, of 1*10 metre 

 diameter, the wave produced by the discharge of the pistol gives 

 an intense sound when it reaches the other end B after having 

 travelled 1590 metres. After one reflexion at B it returns to the 

 point A, whence it started. Its entire path has then been 3180 

 metres. Its sound is found to be weakened, but it still has suffi- 

 cient intensity to be heard outside without there being occasion 

 to remove the membrane J which closes the opening A. After a 



* As stated by the author, the details of the experiments are still un- 

 published; reference is, however, made to them in this Compte Rendu. 

 Judging only from what is herein stated, it appears to the translator that, 

 for detecting and measuring the velocity of inaudible waves, the author 

 closed one or both of the ends of his tubes with elastic thin iron plates 

 (membranes) which marked or were marked by strips of blackened paper 

 passing with uniform velocity over them. It does not appear whether the 

 marking was continued while the air in the tube was at rest, and ceased at 

 the moment of the arrival of the wave, or whether the mark was only made 

 when the wave arrived. In either case, of course, the length of the strips 

 of paper between the successive marks (or interruptions of marking) would 

 be measures of the velocity of the wave. This suggested explanation of 

 what might perhaps otherwise not be clear is, of course, only made under 

 correction. — F. G. 



f "Dans la grande conduite, du diametre de 1*10 metre de Vegout Saint 

 Michel." I suppose this is a gas-pipe (certainly enormous) laid in a sewer. 

 Is it the sewer itself? It does not much matter. — F. G. 



X Probably a thin metallic plate. In this case it appears that both ends 

 of the tube are closed. — F. G. 



M2 



