Zu^ 2C. 



in conflict with the suggestion that the dome over large charges may consist 

 chiefly of spray, for a charge of an ounce throws spray to a height of a few 

 feet at most. The explanation of the difference may possibly lie in an in- 

 fluence of surface tension upon spray formation. Since the pressure under a 

 curved surface is p •= 2T/r In terms of the surface tension T and the radius 

 r, the relative effect of surface tension, when the pressures are unchanged, 

 will be the same only if T is changed in the ratio of the linear dimensions. 

 Thus surface tension, being actually constant, will have a much larger effect 

 upon small-scale than upon large-scale phenomena. 



On the other hand, as we have seen, a dome of superficially solid 

 water is limited chiefly by air pressure, hence it should follow the usual 

 linear scale. The absence of a noticeable dome over small charges is thus 

 consistent with the estimate of possible dome heights as made in the forego- 

 ing, and in turn constitutes evidence against the supposition that the dome 

 over large charges consists largely of moderately disintegrated water. 



It must be recognized, however, that other causes are possible for 

 the difference In the surface phenomena on large and small scales. For one 

 reason or another, cavitation might occur more easily in the salt water of 

 the sea than In the fresh water in the laboratory. Or It might be that water 

 can stand higher tension for the shorter times involved in the action of 

 smaller charges. More evidence on these points is needed. 



REFERENCES 



(1 ) Work of the Explosion Research Laboratory at Woods Hole with 

 plezo gages by R.H. Cole, in National Defense Research Committee Division 8 

 Interim Report of 15 Noveruber - 15 December 19^+2. 



(2) "Cavitation in an Elastic Liquid," by E.H. Kennard, Physical 

 Review, vol. 63, p. 172, 19^3. 



(3) Superintendent of Mining, Portsmouth (England) Report on 

 "Explosive Trials against Ex-German Submarines," M.S. 3/21, Part II, dated 

 1 6 June 1 921 . 



(4) "Report on Underwater Explosions," by E.H. Kennard, Volume I( 

 of this compendium. 



(5) "Pressure and Impulse of Submarine Explosion Waves on Plates," 

 by G.I. Taylor, R.C. 235, 19'+'1- 



(6) "Effects of Underwater Explosions: General Considerations," 

 by E.H. Kennard, TMB Report 4.89, 19/^2 



