163 
3 [ GENERAL SURVEY 
2. EXPLOSION PHENOMENA 
as indicated roughly in Figure 1. The impulsive wave or pressure wave, as it is con- 
monly called, travels eventually at the speed of sound, and may then be regarded as 
an intense sound wave; but at first its velocity should be much greater than the or- 
dinary speed of sound. As the wave moves outward, both the pressure and the particle 
velocity in it decrease; when the distance r from the center exceeds about 10 times 
the radius of the mass of explosive material, the decrease is nearly in proportion to 
1/r, as in ordinary sound waves, but at first the rate of decrease should be much 
greater. The length of the pressure wave in the water, according to Hilliar's mea- 
surements, Cie is of the order of 10 times the radius of the original mass of ex- 
plosive; hence at a given point the duration of the pressure is one to several mil- 
liseconds. 
The form of the pressure wave as indicated by Hilliar's measurements is 
shown in Figures 1 and 2. Figure 1 refers to a brisant explosive such as TNT. Fig- 
ure 2 shows the wave from black powder, in which the rise of pressure is more gradual. 
® 
2 5 
el wo 
wo wn 
: 2 
S a 
Time Time 
Figure 1 - From a Brisant Explosive Figure 2 - From Black Powder 
The ordinate shows the pressure in the impulsive wave as observed at a given 
point in the water, as a function of the timet. 
The same figures also serve to represent the distribution of pressure in 
the water at a given instant, in a wave being propagated toward the left. 
The true curves, however, are doubtless more or less wavy or even oscilla- 
tory. Furthermore, several lines of evidence point toward the occurrence of repeated 
impulses, following each other at intervals much longer than the time occupied by one 
impulse. These impulses are believed to be due to oscillations of the globe of ex- 
ploded gas. 
I. GENERAL SURVEY 
3. AFTERFLOW 
3. THE AFTERFLOW 
It is well known that in a spherical wave the particle velocity consists 
of two components (Appendix I, Section 1; topic: Spherical Waves). One component 
* Numbers in parentheses indicate references at the end of this report. 
