OF THE FLAME IX THE EXPLOSION OF GASES. 
339 
PAET V. 
On the Initiation of the Detonation-Wave and on the Wave of 
“ Retonation.” 
[In conjunction with II. H. Jones and J. Bower.) 
Several of the photographs previously described have illustrated the abrupt spring 
with which the detonation-wave is started. Sometimes, apparently, one such abrupt 
change alone occurs, marking the place where the gradual acceleration of the 
explosion changes; ou other photographs one or more abrupt changes occur in the 
acceleration before the final spring which marks the detonation-wave. Figs. 29, 30, 
and 33 show one or more such sudden changes in the curve always accompanied liy a 
luminous wave thrown back through the ignited gases. 
The' strongly luminous wave thrown back from the point where the detonation is 
started I propose [nominis egestate) to call the retonation-ivavc. This wave has not 
the same constant characteristics that mark the detonation, but when generated 
under certain conditions it resembles detonation most closely. Fig. 43 (Plate 14) 
shows a wave of retonation travelling parallel with and therefore at the same velocity 
as the collision-wave. Fig. 44 shows a retonation-wave travelling more quickly than 
the wave reflected from the end of the tube. A study of a number of photogi’aplis 
leads to the conclusion that the retonation is faster and more luminous when no other 
bright waves have been tlirown back by the advancing flame before the point of 
detonation is reached. 
In considering the cause of the intensity of the retonation-wave we must remember 
the facts illustrated in many of our photographs on collisions. The collision of two 
flames, in which detonation had not yet lieen determined, gave rise to reflected waves 
more rapid and more luminous than the incident waves. Fig. 25 shows this for both. 
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. In the initial period the molecules of the gas 
might meet many times l)efore chemical reaction occurred; in the detonation-wave 
the molecules miglit ]je so intensely agitated that most collisions between chemically 
opposite molecules would result in chemical change. 
At the point of detonation the rise of pressure must be exceedingly rapid owing to 
2x2 
