42 



HILL 



[PHAP. ^ 



•\ 



* 



Fig. 2. The barium titanate pressure -sensitive element and part of tlie preamplifier of the 

 hydrophone used below sono-radio buoys. Scale in inches. 



Hydrophone 



-* 100 ft ► 



Fig. 3. The rigging of the hydrophone below a sono-radio buoy. 



