60 



5. I4IGRATI0N OF A SPHERICAL 3U33LE 



The motion pictures from which Fig. 2 was constructed 

 showed the migration effect mentioned in the introduction: the 

 center of the gas bubble was observed to rise slightly up to the 

 time of maximum size and later to sink rapidly, with periodic 

 fluctuations, through a distance of several inches. Only after 

 the pulsations had practically ceased did the bubble rise again. 

 The explanation of this phenomenon, interestingly enough, ap- 

 peared automatically as a by-product of an attempt to understand 

 the deviations of the points of Figure 2 from the theoretical 

 curve, in a way which will now be described. 



It will be noticed that the theoretical curve is too 

 broad, and that there seems to be a slight asymmetry in the 

 experimental curve. Now the theory from which the curve was 

 constructed has disregarded a number of factors, of which the 

 most important are: 



(1) The gas pressure (responsible for the terra G in ($)) 



has been disregarded, 

 (ii) The water has been assumed incompressible, so 

 that the damping effect of acoustic radiation 

 has been ignored, 

 (iii) The bubble has been assumed spherically 



symmetrical, 

 (iv) The explosion has been assumed to take place in 

 an infinite body of water. In the photographs 



