Se 
1484 
covered in NavOrd 424. The derivation of equation (19) extends 
the treatment to include higher order reflections. 
Experimental verification of the character of the phase distortion. 
3.1 Experimental pressure - time curves were obtained by 
cathode ray oscilloscope recording of signals from tourmaline 
piezoelectric gauges>. The overall, effective high frequency 
response of the system depends upon the size of the gauge, 
which in turn is selected on the basis of expected pressure 
amplitude and corresponding sensitivity requirements. Gauge 
diameters varied from 1/2 to 1 inch, and it is estimated that 
the frequency at which the response would be down to 70% of 
midband would be 30 and 15 ke. respectively. (The high frequency 
response oft the amplifiers was known to be much higher than tnat 
of the gauges.) 
Cathode follower preamplifiers were used to obtain high 
input impedance. The low frequency response was determined by 
the overall time constant of the oscilloscope amplifier and is 
estimated to be down to 70% of midband at O.1 cycle per sece 
The experiments were performed with 1/2 1b. pentolite 
charges and 25 and 55 lb. TNT charges in Vineyard Sound off 
Naushon Island near Woods Hole. Gauges were placed at a depth 
of about 25 ft. below the surface; charges at about 40 ft. Heavy 
tidal currents in this region insure rapid mixing of the water, 
which was always found to be very nearly isothermal over its 
average depth of about 70 ft. 
~ §u 
