Propagation of Waves in Gaseous Media. 165 



upon iron columns in a large vaulted gallery. When the wave 

 first passes, a very loud noise is heard outside, in whatever part 

 of the course the observer is situated. Consequently a consi- 

 derable part of the vis viva is thereby scattered abroad. The 

 same takes place at the extremities and at all the openings fur- 

 nished with membranes. This loss necessarily continues after 

 the wave has ceased to have sufficient intensity to affect the ear; 

 and it is, strictly speaking, sufficient to explain why the sound 

 becomes extinguished, and how the wave becomes so enfeebled 

 as no longer to disturb the most sensitive membranes. But I 

 do not think that this is the only cause at work. There is 

 another which arises from an action of the solid wall upon the 

 gas, whose elasticity it sensibly diminishes. I shall give a proof 

 of this immediately. 



II. Laplace^ s formula does not contain the expression of the 

 intensity of the wave. According to this formula the rate of 

 propagation of a wave is the same, whatever its intensity may be. 

 But according to the more general formula which I have given, 

 this velocity should be greater the greater the intensity of the 

 wave. Now we have just seen that in a straight cylindrical tube 

 the intensity of the wave does not remain constant as has been 

 hitherto supposed, but that it diminishes continual!)', and this 

 the more rapidly the smaller is the section of the tube. The 

 necessary consequence of this is that the rate of propagation 

 of a wave in a tube ought continually to diminish as the wave 

 advances; and this diminution should be the more rapid the 

 smaller is the section of the tube. This is, in fact, what occurs 

 in all my experiments. I shall confine myself here to the dis- 

 cussion of the mean velocity of a wave produced by the discharge 

 of a pistol, and which travels through dry air at 0° C, such a 

 wave being measured from its commencement up to the moment 

 when it ceases to be of sufficient intensity to affect the mem- 

 branes. I select from experiments made upon tubes of the dia- 

 meters 0-108, 0-300, and 1-10 metre. 



(1) Tube of diameter 0*108 metre {Route d'lvry). 



Distances 



Mean 



Distances 



Mean 



traversed. 



velocities, V' D . 



traversed. 



velocities, V . 



Charge of powder 0"3 grra. 



Charge of pov 



T der 0"4 grm. 



metres. 



metres. 



metres. 



metres. 



566-74 



330-99 



1351-95 



329-95 



1133-48 



328-77 



2703-00 



328-20 



1700-22 



328-21 



4055-85 



326-77 



2266-96 



327-04 



5407-80 



323-34* 



2833-70 



327-52 







* This last velocit)^ being indicated on only one band, is perhaps not 

 exact. 



