MOTION OF THE GAS SPHERE 



277 



found that the variation of maximum radius with depth and charge 

 weight agreed very closely with the formula 



(8.10) 



Pofl. 



constant • W 



where W is the mass of explosive and Po the hydrostatic pressure at the 

 depth of explosion. By comparison with Eq. (8.6), it is seen that the 

 right side of Eq. (8.10) should represent the energy available after 

 emission of the shock wave, which Ramsauer computed to be about 



8 



D 4 



o 



< 

 q: 



10 



20 



30 



TIME (msec) 



Fig. 8.2 Measured and calculated radius of the gas sphere from a detonator 

 one foot below the surface. 



forty-one per cent of the total energy. Ramsauer also found that 

 probes placed directly below^ the charge indicated a maximum radius 

 some ten per cent less than that from probes at the side, thus indi- 

 cating upward migration (assuming a spherical bubble). A method 

 basically that of Ramsauer has been used by Bancroft (114) for similar 

 measurements on other explosives. 



Ramsauer's method, ingenious though it is, suffers from the disad- 

 vantage of giving only a limited amount of information concerning iso- 

 lated points on the bubble. An obviously more powerful tool is that 

 of high speed motion pictures of the bubble motions, by methods such 

 as those described in Chapter 6. The earliest records of this kind were 



