214 



PHOTOGRAPHY OF UNDERWATER EXPLOSIONS 



detonation wave strikes this layer and a brilliant flash of light results 

 from emission following excitation of the atoms by the high temperature 

 and pressure of the shock wave in the gas. The duration of intensity 

 can be made very short by decreasing the thickness of the layer, which 

 is excited at supersonic velocity, and the total illumination can be varied 

 by using different charge sizes. A 0.55 pound charge 2.5 inches in 



PRIMACORD 



LEAD SHEATH 



PRIMACORD 



PLASTER OF 

 PARIS 



ARGON GAS 



ARGON GAS 



Co) SPHERICAL (b) CONICAL 



Fig. 6.1 Explosive flash charges for underwater photography. 



diameter with an argon layer 0.19 inches thick has been estimated to 

 give approximately one million candlepower with a duration of about 

 one microsecond. 



Two adaptations of this basic design are shown in Fig. 6.1.^ The 

 spherical charge in Fig. 6.1(a) is detonated at its center by a piece of 

 primacord, a detonating fuse, which is wrapped in a lead sheath to pre- 

 vent initiation of the main charge luitil the detonation wave reaches the 

 end of the fuse. The charge is cast in a plaster of paris mold with the 

 fuse in place, and mounted in a split round bottom flask of larger in- 

 ternal diameter; the two halves of the flask are then cemented together 

 and the air space evacuated and filled with argon. This design from its 

 symmetry gives nearly uniform illumination over a sphere. Charges 

 without the glass flask and argon filling have been found to give remark- 



2 Methods of preparing these and other types of explosive charges are given in 

 reports by Eldridge, Fye, and Spitzer (31), and by Newmark and Patterson (79). 



