PHOTOGRAPHY OF UNDERWATER EXPLOSIONS 



219 



argon-filled tubes excited from an auxiliary charge, the angle and lengths 

 of the tubes giving illumination for 70 microseconds. The resulting 

 streak record, a tracing of which is shown in Fig. 6.2(b), can be measured 

 to give displacement as a function of time, and the velocity then ob- 



REDUCED 



5 10 



DISTANCE R/Oo 



Fig. 6.3 Shock front pressures from velocity data compared with theory 

 and piezoelectric gauge measurements. 



tained by differentiation. Values obtained for spheres of a cast explo- 

 sive two inches in diameter and of density 1.80 are listed in Table 6.1, 

 together Avith shock front pressures computed from Kirkwood and 

 MontrolFs calculations (59, II) for fresh water. The values of both 



1 Measured at a flat surface of explosive. 



Table 6.1. Peak pressures for spherical pentolite charges, calculated from the 



shock front velocity. 



velocity and pressure are uncertain at the surface of the charge, the 

 former because of the rapid change in velocity at this time, and the 

 latter both for this reason and because the shock front calculations 

 have not been extended to these velocities. A minimum value is 



