ILLUSTRATIONS 



Page Figure 



Basic design of horn gap 

 Variety of underwater spark gaps 



investigated 

 Methods used to insulate and encapsulate 



spark plugs 

 High- vacuum switch for energy transfer 

 Plot of acoustic power vs. sound pressure 

 Spark gap before and after firing 

 Laboratory tank and camera installation 

 Pictures of bubble development produced 



in laboratory tank under various 



conditions 

 Deep-water test installation at Lake Pend 



Oreille 

 Assembly for underwater high-speed 



photography 

 Circular spark gap with underwater lights 

 Inside view of spark capsule 

 Oscillograph traces and high-speed photo- 

 graphs of typical underwater spark 



signal 

 33-35 14 High-speed photographs of bubble devel- 



opment at NELPOCS 

 36 15 Arrangement for studying effect of magnetic 



field upon spark gap 

 Experimental magnetic spark gap 

 Typical resonant chamber 

 Waveforms produced by resonant spark 



sound source 

 Resonating coil for underwater spark 

 Spark gap in compliant resonant chamber 

 Waveforms produced by spark source in 



compliant resonant chamber 

 Pneumatic high- power If sound source 

 Molds for rubber spheres 

 Pneumatic spheres of various wall 



thicknesses 

 47-48 2 5 Photographs of bubble development from a 



2- inch sphere 

 49 26 Experimental models of rubber spheres 



51 27-28 Plots of frequency vs. depth for 



pneumatic sound sources 



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