1030 
(b) 
(c) 
(a) 
(i441) Summary and remarks. As shown in Figure 111, the peak pressure of the shock 
wave produced by ca.364 gm TNT at 16.0 in, is 17,050 lbs./in.2, The results 
for both peak pressure and time constant are in essential agreement with 
piezoelectric results obtained at UERL both for small bare charges and depth 
bombs (scaled down). The agreement is within the accuracy of either method 
for these experimental conditions (ca 10%). 
This experimental method has the disadvantage that the results obtained are 
rather sensitive to the geometry of the experiment. For example, to obtain 
the desired accuracy for these shots, the point at which the line from the 
camera lens, perpendicular to the grid, intersected the grid had to be deter- 
mined in the actual set-up to within 1/16 in. For this reason, a single 
rigid frame had to be used to support the camera, the main charge, and the 
grid. It has been demonstrated, however, that the method is satisfactory 
if the experiment is carefully set up. 
Further experiments in fresh water for comparison with those made in salt 
water should be done. 
Spherical shock wave; charge on the optical axis; charge in prid plane. -- 
The theory for peak pressure determination has been worked out for an experimental 
arrangement similar to that of Section (a) except that now the charge is located 
directly in front of the camera (See Appendix II, 2). Figure 112 (Film 526) 
shows a photograph obtained according to this method. 
Non-spherical shock wave; charge on the optical axis; charge in grid plane. -= 
The theory for peak pressure determination has also been worked out for an experi- 
mental arrangement similar to that of Section 3(b) except that the shock wave 
surface is not required to be spherical, but expressible only by some definite 
equation of the form f(x, y, z) = 0 (See Appendix II, 3). 
Spherical shock wave; charge on the optical j charge in front of grid plane. -- 
Partly to increase the amounts of distortion measured on the photograph, and thus 
improve the precision of the measurements, and partly in an effort to find an 
experimental arrangement in which less precision would be necess in setting up 
the apparatus, one photograph (reproduced in Figure 113 (Film 531)) has been 
taken in which the grid was mounted in back of the charge, as viewed from the 
camera. Inspection of Figure 138 in Appendix II, 4 will show how the measured 
distortion is increased by allowing the refracted ray, (considered as projected 
backwards) to traverse a greater distance than in the other experimental set-ups. 
Another evident advantage of this arrangement is that at the time of the photo- 
graph the shock wave need not have reached the grid, so that there is no danger 
of mechanical distortion of the grid. 
In this particular shot, the charge was 250 gm cast pentolite and was placed 51 in. 
in front of the camera. The grid was positioned 8 in. behind the charge, and a 
flash charge 28 in. behind the grid. Since the charge and grid are at different 
distances from the camera, both the shock wave and the grid cannot be in perfect 
focus, but this is not likely to be troublesome if a reasonably small lens aperture 
is used. 
Not enough work has been done using this method to warrant a comparison with the 
method described in Section III, 3, (a). 
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