542 - 4 - 



Having regard to the relatively long interval between flashes, the difficulty of measuring the 

 volufne accurately, and the uncertainty concerning the correct value to 6e assumed for the "virtual 

 mass" of the water moving with the bubble very little accuracy is possible in a diroct measurement of 

 the momentum from the photographs. An attempt has, however, been made to estimate the linear momentum 

 at a timfi- near thf. minimum radius from the photographs and the values of the "raomentum constant" are 

 given in Table III together with the corresponding calculated values (the actual momentum in non- 

 dimensional units is 4 31 rn. where m is the quantity denoted as the "momentum constant"). The observed 



momenta are at any rate of the same order of magnitude as those calculated. 

 This confirms the deduction made from displacement results. 



Conclusions , 



(1) The displacement of the bubble towards the target plate at the first minimum is in reasonable 

 agreement with values calculated from the theory of the attraction of an explosion bubble 

 towards a rigid disc. 



(2) The observed agreement is regarded as indicating that the th-jory provides a correct estimate 

 of the linear momentum of the bubble, except possibly during a very short time near the 

 occurrence of the minimum radius. 



(3) There is considerable discr^jpancy in the predicted ^nd observed v=;lues of the minimum radius 

 and the maximum velocity. This discrepancy in radius and velocity may, however, only occur 

 for a smill interval near the time of minimum radius. 



Feferences . 



(1) Deflection-Time Curves at the centre of box-model plates, resulting from underwater 

 Explosions. 



(2) The Attraction of an underwater Explosion Bubble to 3 rigid disc. 



(3) A Technique for Multiflish Photography of underwater Explosion Phenomena. 



(4) Photographic Measurements of the size, shape and movement of the Bubble produced by 1 oz. 

 charges of Polar immon Gelignite detonated underwater at i depth of 3 feet. 



(5) The Behaviour of an underwater Explosion Bubble. 



(6) The Behaviour of an underwater Explosion Bubble further approximations. 



