1 70 On the Velocity of the Propagation of Waves in Gaseous Media , 



In my Memoir I give two series of direct experiments upon 

 those gases which I have been able to prepare in sufficient quantity. 



The first series was made upon the tubes of 0*108 metre dia- 

 meter in the route d'lvry, the available length of which is 567*4 

 metres. This tube I was able to fill successively with hydrogen, 

 carbonic acid, and coal-gas. 



For the second series, I made use of the little tube in the Col- 

 lege de France, which has the same section but a length of only 

 70*5 metres. I was able to use this tube for carbonic acid, prot- 

 oxide of nitrogen, and ammonia. In the following Table the 

 results obtained by means of both the tubes are thrown together. 



Tube of length Tube of length 

 567'3 metres. 705 metres. 



V? 



Hydrogen .... 3-801 3*682 



Carbonic acid . . . 0*7848 0*8009 0*8087 



Protoxide of nitrogen 0-8007 0*8100 



Ammonia 1*2279 1*3025 



V 



If we compare the ratios =* of the first two columns with the 



calculated values of a/ we find a rather remarkable coinci- 

 dence. The differences would certainly have been less if the 

 experiments could have been performed on pure gases ; but this 

 is very difficult in tubes of such great capacity. Further, the 



values of a /-k are not very exact, because we are often obliged 



to take the theoretical density of the gas with regard to air, and 

 not its actual density, which is the only one really concerned. 



My experiments show that we may accept the law -=r = a / _; 



but only as a law true in the limit (loi limite), a law which gases 

 would exactly satisfy if they were placed under circumstances 

 where they would behave as perfect gaseous media. 



VIII. My experiments for the determination of the rate of 

 propagation of waves in the open air were made by the method 

 of reciprocal cannon-reports. It is clear that at its commence- 

 ment the wave has a very great intensity; but this diminishes 

 very quickly as the wave spreads through space. Further, at the 

 moment of the explosion of the cannon the layers of air next to 

 the cannon undergo a true displacement which still further in- 

 creases the velocity of the propagation. Thus, in consequence 



