1029 
points of mean distance of the light rays behind the shock front should go 
to zero in this limit. The peak pressure obtained from two prints of the 
same shot (Figures 109 and 110) agree to within 4.5% (17,200 and 18,000 
lbs./in.2). Correcting the result from Figure 108 (pig, = 16,700 1bs./in.2) 
to a shock wave radius of 14.4 in., using a distance exponent of 1.13, one 
obtains a pressure of 17,400 ibs./in.2, which agrees with the average of 
Figures 109 and 110 to within 1.5%. 
This method of peak pressure determination was also applied success- 
fully to the other two shots, consisting of ca, the equivalent of ca. 
364 gm TNT and using a shock wave radius of ca. 16 in. Measurements 
were made at several pairs of grid line intersections for each 
of the two films. The values of log p,, were plotted against (IRI - ray) as 
before and one straight line was drawn through the data from both films, 
since the value of iRi, the shock wave radius, for the two films was identical. 
Extrapolation of this line to |R|I - rz, = 0 gave a value for Ppax of 17,050 
lbs./in.2, This plot is given in Figure 111. The average deviation of the 
points from the straight line is ca 5.5%, with no systematic difference 
between the points for the two shots. 
(ii) Tdme-constants. The results for the two torpex shots were also used for 
calculation of time-constants of the shock wave. Since the detailed 
development of the theory, together with a sample calculation, is given 
in Appendix II, only the results will be reported here. In general, the 
calculations are considerably more tedious than for the peak pressures. 
Five points were used in the calculations, two from one shot and three from 
the other. The ones whose images were the clearest, and thus the most 
accurately measured, were selected. They were picked from the plot of 
Figure 111 at different yalues of ({RI - ry) and at different deviations 
from the line. The results of the calculations are shown in Table VI. 
Table VI. Results in the evaluation of time constant. 
— No. Point No. (RI 1 ae 6. ae D,. e, a 
536 22 0.61 B515 14.76 3901 
537 5a 0.63 3.39 4.72 41.3 
537 12 0.94 3.23 4.11 39.6 
536 8 0.97 3.68 14.03 43.8 
537 18 1.13 3.09 13.71 38.1 
Av. @, = 40.4 (sec, average deviation from mean = 1.7 yi deedd 
It will be noted that there is no systematic trend of 0, with distance 
of the point selected for calculation behind the shock front ( {RI -ray). 
47 15518 
