297 
Discussion. 
The calculatlons described above agree better with the observations than did those described 
In Report "A". The pressure¢time curve falls away much more slowly with time, and It seems Ilkely 
that the theoretical curve is monotonic. Probably the most Interesting feature of the present 
calculations is the energy distribution of the disturbance In the early stages. About 65% of the 
energy Is carried by the water by the time that the shock wave front has reached 6 charge radil; 
41% Is useful work and 2% Is unavallable, 
Simllar calculations could be made on other, more powerful explosives, but In the meant ime 
it seems clear that the useful work given to the water wil) Increase with the chemical energy of the 
explosive, but less rapidly than llnearly because the wastage goes up faster, It seems most unlikely 
that an explosive with great energy release will cause energy to be dissipated In the first few 
charge radii so rapidly that Its "damaging effect*® (or more precisely, the useful work left In the 
water) will be less at greater distances than that given by a less powerful explosive, 
Measurements of the pressure-time curves at a distance cannot be used to determine the very 
early stages of an explosion, because of the overtaking effect, described earller, It seems safe 
to say that whatever occurs within 00 microseconds of the detonation wave in a 300 1b, charge 
reaching the surface of the charge Is completely undetectable by measurements at 50 feet. The 
question arises whether the best results at 50 feet might be obtained by preparing the explosive 
in such a way that the pressure does not build up to Its maximum unt!1 100-200 microsecands after 
the detcnation wave has reached the surface. In other words, If aluminium Is present tn an 
explosive mixture for use at a distance under water, there may well be an upper and a lower limit 
to the size of aluminium particles required. 
Description of diagrams. 
Figure 4. Two reversible paths ABC, ADC by which water may be taken from the Initial 
state to the final state of the shock wave transition, 
Figure 2, The pressure and velocity distributions 10 microseconds after complete 
detonation of a 50 cm. sphere of T.N.T., density 1,5, surrounded by water. 
Shock wave at 54.4 cm; Interface at 51.6 cm 
Figure 3. The final version of the 17 step. The two forward, one backward procedure 
gives a tripling of each P and Q curve, but the scale of the diagram Is not 
sufficlent to show all the curves. The & curve Is practically the same 
in all cases; the P, curves vary by about 20 m./second, 
Figure 4. Velocity distribution curve after 24 complete steps (t = 1.25 x 1077 seconds). 
Figure 5. Pressure distribution curve after 24 complete steps, 
Figure 6. The pressure-time curves for a 300 1b, charge at 50 feet. €E experimental; 
T theoretical. The accuracy of the theoretical curve Is not high since It Is 
obtained by an extrapolation of uncertain validity. 
Figure 7. Pressure and velocity distributions at various times t In 10 seconds fora 
charge of Initial radlus 50 cm, 
Figure 8. The useful work and the wastage given to the water In cal./gm. of T.N.T., a8 
a function of the radius of the shock wave x, expressed In charge radlil. 
(A 300 1b. charge, density 1.5, has a radius approximately 11 Inches). 
