1121 
8. Time Phenomena 
The abrupt increase in the rate of decay of pressure with tine, 
which was observed in the records dof Figs. 4 and 5, may be qualitatively 
correlated with the termination of sustaining contributions to the 
pressure by the detonation of new elements of the explosive charge. 
The times at which these breaks should occur may be estimated from 
simple considerations involving the velocity, v, of detonation, 
the velocity, c, of the shock-wave transmission through the sea water 
(assumed acoustic as a first approximation), and the geometry of the 
gauge-charge system. Figure 3 shows the geometric arrangement for the 
three cases involving detonation at one end of the straight line charge. 
Figures 4 and 5 are actual photographic reproductions of typical 
piezoelectric records for the various experimental conditions. In the 
shot illustrated by Fig. 5C, the detonations of the two ends of the 
charge were not simultaneous. It will be noted that the second peak, 
which is barely visible at To = 5 ft, is equal to the first peak when 
[oo 58 ft. The records for this shot are included for interest only. 
No quantitative analysis of any sort was attempted. 
It should be noted that the pressure scales in Figs. 4 and 5 are 
different for the various distances. 
A. Gauge Position A, on Charge Axis, Near Detonator. Let t = 0 
at the time of initiation of detonation. The first signal of the 
explosion then arrives at gauge A at the time 
ty = r,/e (1) 
and the signal from the last element of charge contributing to the 
pressure arrives at the time 
te = ble + (b+ r,)/c (2) 
The difference 
te ft, = be + Iv) (3) 
represents the time after the shock front that the gauge pressure-time 
record should show an increase in the decay rate. This "duration" for 
gauges on the charge axis is seen to be independent, in the acoustic 
aauie 
