- 2 - 

 40 



bubbles after application of a positive pressure; another example 

 is the observation by A, tiviing and his associates at the Woods 

 Hole Oceanographic Institution that multiple shocks are heard 



by a microphone placed near a submerged pipe with a diaphragm at 



2 



one end which is burst by water at high pressure inside the pipe. 



Although this article and the others in this volume are concerned 

 primarily with explosion bubbles, and although additional factors 



such as surface tension may have to be invoked in applying the 



■J 

 theory to tiny bubbles , it is worth bearing in mind that similar 



principles govern a variety of widely different phenomena. 



The essential features of the pulsation phenomenon arise 

 from the fact that an explosion creates a cavity filled with high 

 pressure sas, which pushes the water out radially against the 

 opposing external hydrostatic pressure. The high velocity thus 

 imparted to the water causes it to overshoot the equilibrium 

 radius at which internal and external pressures are equal, and 

 when the external pressure finally succeeds in bringing the ex- 

 pansion to a halt a contraction sets in, which again overshoots 

 and recompresses the gas to a high pressure. This sort of oscilla- 

 tion may be repeated a number of times, until the original energy 

 has become dissipated in one way or another. At each compression 



2 



Private communication from Dr. Ewing. 



3 



See for example R. S. Silver, Engineering 15i, 501 (19^2), 



