1566 
1t is believed that the oscillations noted in the tail of 
the reflected wave do not originate in the gauge response or record- 
ing system, nor in the immediate vicinity of the gauge, for in 
some cases a striking qualitative correlation has been observed in 
the detail of the oscillation as recorded by the several channels, 
It is felt that these small pulses originate in or near the 
cavitation region and may be associated with the formation and 
collapse of bubbles. 
The pressure drop in the reflected wave is always less than 
that to be expected ideally. In Figure 17 the measured ratios of 
reflected to direct peak pressures from 0-5 pound pentolite 
charges are plotted against range, both for the drop to the tip 
of the negative spike and the drop to the level region smoothed 
through the oscillations. The scatter of the data is considerable, 
but the trend is clear. The reflected wave has an amplitude of but 
a few tenths of the direct shock at short ranges and increases to 
an appreciable fraction of it at large ranges. On the same plot 
is shown the ratio to be expected if there were no drastic atten- 
uation due to cavitation. This curve is not horizontal because 
account has been taken of the extra distance traveled by the 
reflected wave in its passage to the gauge. Also displayed is a 
curve showing the ratio to be exvected when a crude account of 
cavitation is taken by the method described below. 
