98 THE EXPLOSIVE WAVE. 



It sometimes happens that the flame does not reach the end 

 of the tube, probably in consequence of the insufficient heating 

 of the sections in advance of the mixture in ignition. One of 

 the trials led to some important observations on this point. The 

 flame being stopped in its course, without however going out, 

 the aqueous vapour, condensed behind it, produced a backward 

 draught upon the gas, and a return of the flame was observed 

 very clearly towards its starting-point, this movement lasting 

 during a very appreciable interval of time, a second, perhaps, 

 for a distance of 2 metres. This shows well the difference 

 between the progressive combustion of the gaseous compound 

 and its detonation properly so called. 



Diameter of the Tubes. In order to investigate more fully 

 the influence of the diameter of the tubes, it was thought 

 advisable to make fresh measurements with a leaden tube, the 

 internal diameter of which was equal to 15 mms., i.e. three 

 times as great as the preceding one, and 30 '43 metres long. 

 Three experiments gave 2754, 2975, 3019 metres; mean, 

 2916 metres. 



The experiments made with a leaden tube, the diameter of 

 which was equal to 5 mms., having given 2841 metres, we see 

 that the velocity is to all intents independent of the diameter 

 of the tubes, reckoning from 5 mms. 



It must be noted, however, that in a capillary glass tube 

 (diameter 1*5 mms.), the velocity was found to be equal to 

 2341 metres, i.e. it was somewhat lower. 



Closing of the Tube. It may be asked is the rate of pro- 

 pagation of the detonation the same whether the tube be 

 open or closed ? It is only the latter case that strictly fulfils 

 the conditions of combustion within a constant volume. To 

 meet this question, experiments were made (with the caoutchouc 

 tube), leaving open first the orifice farthest from the point of 

 ignition ; then the one nearest to this point ; and, finally, both 

 at once. 



Three experiments of this nature gave 



Velocity per second. 



The farthest orifice only being open ... 2645 metres. 

 The nearest orifice only being open ... 3052 ,, 

 The two open together ... ... 2766 



Mean ... 2821 



The mean, with the same tube entirely closed, was 2810. 



Thus the velocities have been found to be to all intents the 

 same in all four cases. We see by this that the propagation of 

 the detonation is so rapid that while it is taking place the gases 

 are not projected forward, and have not time to escape from the 

 tube to any appreciable extent at least, in narrow tubes. This 

 is explained by the fact that the detonation proceeds more 



