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Prof. H. B. Dixon. On the Movements [June 5, 



Part V. — On the Initiation of the Detonation-wave and on the Wave of 



Retonation. 



[In conjunction with E. H. Jones and J. Bower.] 



Our photographs show abrupt changes in the acceleration of the 

 explosion before the final spring which marks the detonation-wave. 

 These sudden changes are accompanied by a luminous wave thrown 

 back through the ignited gases. 



The strongly luminous wave thrown back from the point where the 

 detonation is started we call the " Betonation-wave." A study of a 

 number of photographs leads to the conclusion that the retonation is 

 faster and more luminous when no other bright waves have been 

 thrown back by the advancing flame before the point of detonation is 

 reached. 



The collision of two flames, in which detonation had not yet been 

 determined, gave rise to reflected waves more rapid and more luminous 

 than the incident waves. Now these reflected waves could not owe their 

 increased velocity to the mechanical impact, which could only result in 

 the reflected waves being copies of the incident waves. It is evident 

 then that chemical action must occur to assist these reflected waves, 

 and, therefore, the combustion is obviously not complete when these 

 waves return. From this it would appear probable that the period 

 before the detonation is distinguished not only by a slower propagation 

 of the flame, i.e., of ignition, but also by a slower process of combustion. 



At the point of detonation the rapid rise of pressure produces not 

 only the forward wave — that of detonation — but also a backward wave 

 of compression into the gases still slowly burning behind it. This 

 compression-wave must raise the temperature of the ignited gases and 

 quicken the residual burning ; its propagation would thus be analogous 

 to that of the detonation-wave, but modified by the extent to which 

 the slow combustion had proceeded. 



The retonation- wave attains its greatest rapidity and brightness 

 when it is developed at the closed end of a tube, i.e., when the gas is 

 fired at such a distance from the closed end that the explosion, 

 gradually increasing in intensity, just reaches the detonation point as 

 it arrives at the stopper. Under such conditions the reflected wave is 

 superposed on the wave of retonation, and the result is a wave which 

 Cannot be distinguished from a detonation-wave. 



As regards the dark space formed at the point where the detonation- 

 and retonation- waves originate, it is no doubt a space of cooler gas. It 

 persists for some time, and its damping effect on the passage of collision- 

 waves can be observed in several of the photographs. 



