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shock front by means of the data of Kirkwood and Montroll. o/ Since the distance 
between the shock wave and the piezo gage at position A was only 2.25 in. at the 
instant of the photograph, these corrections amount to less than 0.25 in. 
4 similar experiment was carried out with the shock wave charge just out of the 
field of view and with a diffusion screen between the flash charge and shock wave. 
The whole set-up, shown in the diagram below, 
Screen += Positions of 
Piezo Gauges 
Camera 
Flash Charge 
and Reflector 
@+ 
Charge 
Figure 126 
is similar to that used in this laboratory for cavitation studies. The resulting 
photograph is show in Figure 129. From it one obtains a distance of 3.44 in. 
from the shock wave to the piezo gage as compared with a value of 3.36 in. calcu- 
lated from the piezo records. 
A third experiment compared the image of the shock wave with the projection of its 
shadow on a translucent screen. No piezo gages were involved. Two translucent 
paper screens were put in the same plane with the shock wave charge and perpendicu- 
lar to the line from the camera to the charge. The charge and screens as viewed 
from the camera are sketched below: 
pistieto 20 Fea. 
The whole set-up is shown from the top in the following sketch: 
Figure 128 
ssure wave produced an underwater explosion IJ, July 1, 1942, by J. G. 
Kirkwood and E. W. Montroll, OSRD Report 670. 
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