1400 
Figure 4A shows, for example, a typical shock-wave record 
in the acoustic region, while Fig.4B shows the record at the 
same pressure level for a much more oblique incidence, Here, 
no measurement of Tp may be made since there is no apparent 
rarefaction front. With charge and gauges at the same depth, 
D, results were obtained for varying D. These are shown in 
Table I for those angles of incidence at which measurements of 
Tp were possible, 
TABLE I 
GAUGE CROSSING TIMES 
Average 
Tg 
V. RESULTS 
4. Low-Pressure Series 
Because the first series of shots was made in sea water with 
surface ripple always present, a charge depth of 2 ft and gauge 
depths of 1, 2, and 3 ft were used, these being the shallowest 
values at which depth variations due to ripple could be considered 
negligibly small. At such depths relatively large charge-to-gauge 
distances were required, to obtain small incident angles, & in 
Fig. 3, and -the pressure levels at the pote of incidence, S, 
were consequently quite low. Values for W 3/R at point § 
varied from 0. 364 (corresponding to a free water similitude 
pressure of 8200 psi) at an angle, «, of 51.2° down to 0.024 
(535 psi) at & = 3.8°. 
Experimental pressure and duration results obtained under 
these conditions show no great deviation from the values predicted 
by Kirkwood for pressure in free-water, or from the durations 
predicted by the acoustic theory. As shown in Table II, the only 
duration measurement that shows a significant difference 
from the acoustic value was obtained for the smallest angle of 
incidence in the series and the lowest surface pressure. On the 
other hand, the individual pressure-time records, of which repre- 
sentative examples are shown in Figs. 9-13 reveal curves that 
deviate considerably from the free water exponential decay 
pattern. Note, for example, how the decay curve varies for a 
2 ft gauge depth as the charge-to-gauge distance is increased, 
ae 
