708 
Ba Oia 
over the regions from t = 0 to t # 9, where t is the time measured from the 
peak and @ is the time constant of the shock wave. The response of mechan- 
ical gauges to the shock wave is some function of the initial portion of 
the pressure-time curve out to a time t corresponding to the completion of 
action of the particular gauge. Thus mechanical gauges with a response 
time that is short relative to the duration of the shock wave measure quan- 
tities associated closely with the peak pressure, while gauges with long 
response time measure quantities related more to the impulse of the shock 
wave. These measurements are with respect only to the primary shock wave, 
and are not affected by secondary pulses resulting from oscillations of the 
"bubble" in the water, although the piezoelectric gauges may be used for 
this purpose when so desircd. 
Due to the urgency of the work at the time it was undertaken it was im- 
possible to complete the instrumentation before the actual comparison of ex-— 
plosives was begun. Thus during the early experiments only 2 piezoelectric 
gauges and a few diaphragm, ball-crusher and Modugno gauges were used on 
each shot, while in later experiments as many as 8 piezoelectric gauges, 25 
ball-crusher, 8 diaphragm, 8 Modugno, and 8 Hilliar—type momentum gauges 
were used. While the early work may have suffered somewhat because of the 
small amount of instrumentation, it was nevertheless possible to produce 
useful results that could not otherwise have been obtained. 
The greater part of the work of the RELIANCE has been in the comparison 
of various explosives in standard service weapons, such as depth bombs, 
depth charges, and aircraft—dropped mines. Other types of more fundamental 
research have been done whenever possible, including the determination of 
similitude curves from spherical charges, the study of the pressure ficld 
about line charges and multiple charges. 
