1005 
water-air interfaces were provided by filling with air to hydrostatic pressure a 
6 in. pipe open on the bottom as shown in Figure 50. Other experiments were 
carried out substituting a 20 x 10 in. sheet metal trough for the pipe, and 
finally by using the surface of the sea on a calm night. It was found that such 
a critical angle existed ani was greater for greater size of surface. 
Ocean surface to compressed air supply 
Interface 
a Primary 
95 shock 
Reflected wave 
tension 
wave 
25g tetryl charge 
Figure 50. Sketch showing experimental arrangement for Figs. 51 = 56. 
The results of the experiments with the six in. pipe are listed in Table IV, 
and six representative pictures are shown in Figures 51, 52, 53, 54, 55, and 56. 
The critical angle is about 70° for the conditions of these experiments. 
Table IV Data of riments on Oblique Reflection of 
Shock Waves from Water-air Interfaces 
Distance, Angle of Estimated 
Charge Charge to Incidence Peak 
Film Weight Shock Front p Pressure 
No 8 in degrees 2 Cavitat 2 
256 25 23 1/2 0 3700 yes 
270 250 45 45 4200 yes 
258 25 22 1/2 50 3900 yes 
261 25 19 1/2 56 4500 yes 
264 25 19 1/2 62 4500 yes 
265 250 45 1/2 69 4100 no 
259 25 21 70 4200 no 
267 25 20 1/2 71 4300 ? 
269 250 46 71 4100 no 
257 25 23 90 3800 no 
With the large trough, pictures have been taken up to 80° and, using the surfac 
of the ocean, up to 83°. Cavitation was present in all cases, although it was 
much fainter at the larger angles. See Table V for complete date and Figures 
57, 58, 59, and 60 for typical examples. 
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