27 
76. The reflected pulse is produced in effect by a "negative" charge 
above the water tending to suck the water towards it. The particle 
velocity in the water due to the reflected pulse is thus upwards, that is, 
in the same direction as that due to the original pulse. If the 
cavitation tension E F is very small, the tension in the reflected pulse 
will be approximately uniform throughout the thin layer A D and equ’.1 to 
the pressure, similarly uniform, due to the original pulse. Each pulse 
will then contribute approximately equal particle velocities and the total 
particle velocity will be approximately twice that due to the original 
pulse. Considering the first very thin layer and using equation 17 the 
velocity of upwards projection of this first layer will be 
2Pn 
Mie ~ fo eco eee eee eee eee eee eco eco (27) 
where py is the pressure at the pulse front. For the next layer the 
same type of formula would hold but P,, represented by DF in fige 12b, 
is replaced by the slightly smaller pressure represented by D E. Since 
the pressure in the original pulse decreases steadily each successive 
layer will be projected with slightly smaller velocity than the preceding 
layer. In particular, therefore, the top of the dome is formed by drops 
from the first initial layer and attention will be concentrated on this 
layer. 
77- So far, only a point 
immediately above the explosion has 
been discussed. In fige13, B 
represents the charge and E' its 
image in the sea surface A C. 
Consider a point P in the direction 
E P making angleO with the 
vertical. Due to the original 
pulse, the initial particle velocity 
at P is u, in the direction E P, 
whilst due to the reflected pulse 
it is u, directed along PE'. The 
resultant velocity v of the water 
projected initially at P is thus 
{ 
! 
(ae 1 oe 2Pm 
a es h>7 iy v = 2u,cos0 = oS cos 2. «.- (28) 
where By refers to the maximum 
pressure at P. Since Py, and u, 
vary inversely as the distance E P, 
Fige13 - Resultant velocity of the variation of v along the surface 
projected water for a given weight and position of 
charge is of the form 
Votcod O's.) ae (29) 
