1398 
and the ratio P,/P, is 1.07. The ratio remains roughly the 
same for all values of wl/3/R used in this study, and it was 
therefore concluded that, had extrapolation been possible 
in the results here presented, the values of P, would have been 
7 per cent higher than the values of P, obtained. A derived 
peak pressure, Pp = 1.07 Pag, is therefore presented as an approxi- 
mation of Pp. 
mo 
oa 
a 
a, 
~ 
® 
5 
7) 
n 
® 
f4 
A 
Time (microsec) 
Fig. 2. Free-Water Pressure-Time Curve for 250 gm 
Pentolite Charge. 
3. Time Duration Measurements 
In the accompanying tables, computed values of shock-wave 
duration, t, are given as derived from acoustic theory. These 
values were obtained from the geometric configuration of the 
rig, as shown in Fig. 3, and are derived from the differences 
in path length traveled by the direct shock wave and the re- 
flected tension wave, assuming that both travel with the speed 
of sound, The experimental measurement corresponding to this 
value is called T and is taken as the time interval between the 
top of the rise line, at which instant the gauge is recording 
the apparent peak pressure, and the point at which the pressure 
returns to the hydrostatic value. For gauges small relative to 
the thickness of the shock wave, this corresponds to the time be-~ 
tween the arrival of the shock wave at the edge of the gauge 
farthest from the charge and the subsequent arrival of a steep- 
fronted rarefaction wave at that point. 
=—6= 
