1075 
_- 3 - 
figure 3, there is evidence of a shock wave moving ahead of the spray. In the case of 
figures 3 and 4 the water surface, which was illuminated by bright sunlight, has recorded. 
woz, charges. 
Figures 6, 7 and & show selected frames from the Marley camera records. 
Evaluation of records. 
16-1b. charges. 
The distance vertically above the charge which it was necessary for the shock wave or 
vater plume to travel in order to intercept the light pencils subtended at the camera by the 
lamps was deduced from the geometry of the layout. A reduced distance scale corresponding to 
the position of the charge was obtained in this way. (The error in height introduced by 
assuming that the shock wave first cuts the light pencils vertically above the charge instead of 
slightly nearer to the camera, is very small). 
. 
From the records time—-displacement curves have been plottrd, In the case of records 3 
and 4 the trace terminations were not sufficiently well defined to give a satisfactory displacement 
qrve for the water surface. 
Velocity curves have been plotted from the displacement curves and these are shown in 
figure 5, compared with the corresponding results in (4) sealed up, 
4-oZ, charges. 
The distance’scale for the Marley camera records was obtained by taking a record of a 
graduated pole supported vertically over charge position. From this scale time-displacement 
qurves for the water surfaco havo beon plotted. Deduced velocity curves are shown in figure 9, 
compared with the corresponding acetylene jet results reported in ({). 
Discussion of results. 
tn (2) a table was given in which water surface and air shock wave velocities were 
tabulated with the corresponding pressures in the water surface and the air shock wave. This 
dat. can be used in conjunction with the curves given in figure 5 to obtain values for the 
water and air shock pressures at various heights above the undisturbed water level. 
As in the case of the previous 4~oz. charges the velocities fall off rapidly so that it 
is difficult to extrapolate back to initial velocities with much accuracy. On the basis of such 
extrapolated values however, the pcak shock pressures in the water surface obtained are 135, 
42 and 34 tons/sq.in at depths of 8, 16 and 32 in. respectively, The corresponding figures 
calculated from the Penney and Dasgupta formula for charges at depths of 2, 4 and 8 charge radii 
are 61, 19 and 7 tons/sq.in. and those calculated from the later work of Temperley and Craig 
are G1, 25 and 8 tons/sq.in 
There is evidence to suggest that the detonation process in the T.N.T. was initiated 
near the detonator and not at the centre of the charge. This may in part account for the high 
experimental results at the shallow depths. The disagreement between theory and experiment at the 
32-in, depth is probably attributable to thc unsatisfactory character of the record (figure 4), 
interpretation of which is particularly difficult over the first 2 ft. above water level, 
u-0Z. charges. 
The Spray velocities obtained by the Marley camera technique, figure 9, are in reasonable 
agreement with the drum camera results given in (1), except at the 2-in. depth. Extrapolation 
gives initial spray velocities of approximately 3209, 1300 and 580 ft./sec, respectively for the 
2, 4 and 8 in. depths corresponding to peak shock pressures in the water surface of 78, 24 and 
9.5 tons/sq.in, respectively for the three depths. 
'f, as in (2), the charges are regarded as 2-in. diameter spheres of C.E, at depths of 
2, 4 and 8 charge radii, the results agree closely with the theoretical values given above. 
(For comparison with T.N,T. the experimental results should be reduced by about 5%). 
CONCIUSION sesee 
