PROFESSOR II. B. DIXON ON THE MOVEMENTS 
;U0 
the increase of chemical action, and this pressure would produce not only the forward 
wave of detonation, hut also a sudden backward wave of comjDression into the gases 
still slowly ljurning behind it. This compression-wave must raise the temperature of 
the ignited gases and so cpiicken the residual burning; its propagation would then be 
analogous to that of the detonation-wave, but modified by the extent to which the 
slow comljustion has proceeded. I believe this view accounts for the facts described 
and also for the phenomena observed in the initial period of the explosion (see 
Part VI.). 
Tlie retonatlon-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 
tlie 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 true detonation. Fig’. 45 shows the retonation-wave 
developed at the closed end of the tube in the mixture CnH^-l-20o. 
Fig. 46 shows the formation, propagation, and collision of two retonation-waves 
produced hy firing the gases in the middle of a long tube. The picture shows the 
two flames travelling from the spark to the light and the left, and the two points of 
detonation at either edge of the film. The two retonation-waves return symmetri¬ 
cally to the centre and tliere come into collision, producing reflected waves. If we 
compare this photograph with fig. 47 or with fig. 48, we see the effect of the 
retonation-waves starting from the two ends of the tube. If the point of detonation 
occurs just before tlie end of the tulie is reached, the reflected wave runs back nearly 
parallel witli tlie retonation-wave, as is shown in fig. 49. 
In order to make a direct comparison of the velocity of the retonation-wave 
starting from the end of the tube with the detonation-wave, two tubes were fixed 
jiarallel one above another, and were filled with the same gases. One tube was 
connected with a long leaden pi^ie, in which the explosion was started, so that the 
detonation-wave alone traversed the glass tube ; the second glass tulie was fitted 
with firing wires at one extremity, so that the initial phase of explosion up to the 
detonation point sliould just occupy its length. The t'sro flames were then jihoto- 
graplied simultaneously on the moving film. 
Fig. 50 shows the detonation-wave in tlie mixture ( moving Irom right 
to left in the lower tube, and jirst aliove the point where it meets the closed end ot 
its tube the beginning of the explosion in the second tube can be seen. The second 
flame travels .slowly from left to riglit, striking the end of the tube at the detonation 
point. Its intense retonation-wave, i-eturning from right to left, travels in a line 
parallel with the detonation in the first tuhe, fie., their velocities are ajiparently 
ecpial. The same tiling is shown in fig. 51, where the mixture used was CS,, -fi 60^. 
In the lower portion of the picture the flame is .seen travelling slowly from left to 
right in the first tube ; it ciusses the image of the detonation-wave, which is travelling 
