164 
I. GENERAL SURVEY 4 
3. AFTERFLOW 
is exactly proportional to the excess pressure, as in plane waves. The second compo- 
nent represents an additional motion that is left in the water by the wave as it trav- 
els outward. This component, possibly representing the "surge" of some writers but 
called here the afterflow, tends to be inversely proportional to the square of the 
distance from the point of origin of the waves. The afterflow is important, there- 
fore, only close to the source. 
II. THE EXPLOSION| 
II. THE EXPLOSION 
It will be assumed that the explosion process is of the type called deto— 
nation. In such a process a detonation wave, initiated at one point, sweeps through 
the explosive material. The front of the detonation wave is extremely steep. Each 
particle of the material, as the front passes over it, undergoes a sudden and fairly 
complete chemical change, its temperature and pressure rising to very high values; at 
the same time the intense pressure gradient in the detonation front imparts to the ma- 
terial a high forward particle velocity. Behind the detonation front, the pressure, 
temperature and particle velocity tend to fall off gradually to lower values, which 
are determined in part by conditions elsewhere in the exploded material. 
The velocity of propagation of the detonation wave, or detonation velocity , 
D, is a constant for a given kind and density of material, provided the dimensions of 
the mass are not too small. Observed values of D for several substances, and a few 
estimates (not very reliable) of the maximum pressure p,, and centigrade temperature 
tm in the detonation front, are as follows (1), (2) and (13) [cf. also (20)]: 
Picric Acid TNT 
20, 700 23, 700 22,700 
1.61 x 106 
3780 
D, feet per second 
Pp, » pounds per square inch 
t,,, degrees centigrade 
When the detonation wave reaches the surface of separation between the ex- 
plosive and the water, it is partly continued as a wave of high pressure in the water, 
partly reflected as a wave of expansion traveling back through the exploded gas. The 
initial pressure in the water wave, however, should be considerably less than the 
pressure in the detonation wave itself. 
The waves set-up in the gas globe may strike the surface of separation be- 
tween gas and water repeatedly, and in this way oscillations may be produced in the 
pressure wave that is sent out through the water. Furthermore, in actual cases, the 
detonation wave may reach different parts of the surface of the explosive at differ- 
ent times, depending upon the shape of the mass of explosive and the location of the 
