1571 
where weight is in pounds, distance in feet ,and time in milliseconds. 
Inserting (150), and (151) into (148): 
Ya 
bn wy 2 oe = 
Pa + H(Rcos8-a)+ t/t) p y,0) PGE) = Pe (153) 
To find Wi at any point (R,],6) one calculates Ro and X% by 
(149), @ by (152),and finally W; from (153). The limits of the 
cavitation region are found by varying Ry at a fixed 6 5 the value 
of R, which makes Wi = W determines a point on the upper boundary of 
cavitation and that which makes Wj a minimm, Wnin, determines 
@ point on the lower boundary. On this particular ray, according 
to (¢) we then set Wi = W above the cavitation and Wi = Wysy, 
below. The process is repeated for other values of @ until the 
cavitation region is mapped to the degree desired. 
The cavitation region found in this way, due to the explosion 
of a 0-5 lb. pentolite charge 40 feet below the surface is shown in 
true scale in Figure 18a. It is seen to be a thin layer of wide 
extent near the surface, though never touching it. In 18b the same 
region is shown with an eight-fold magnification in depth scale. 
Here the shading is meant to imply qualitatively that the cavitation 
is most vigorous along the top side of the region and gradually 
dies out to nothing along the bottom and at the outer tip. 
The pressure drop in the reflected wave arriving at the 
Ww 
o3 ,2), computed for the gauge position. 
The theoretical curve of Figure 17 was obtained in this way. In no 
gauge is taken to be P< 
case was the receiving gauge theoretically in the region of cavi- 
tation in this particular series of measurements- At small ranges 
