9 93 
(7) Variation of Pressure with Distance. 
This was investigated by hanging gauges at different distances D in the same 
radial direction from the charge. The results, which are recorded in Table IIL, were 
calculated in the form— 
Pressure (or time integral of pressure) at distance D, _ (as 
Pressure (or time integral of pressure) at distance D, D, 
It will be seen that the maximum pressure appears to fall off slighty more than 
in proportion to the distance (x > 1), but roughly speaking the time-pressure curve at 
distance D, is a copy of the curve at distance D, with all the ordinates altered in the 
proportion a Examples are shown in Figs. 14 to 18, 20 and 23. 
2 
The results indicate that the wave spreads with very little dissipation of its 
energy. 
TaBLe III. 
D = distance in teet from centre of charge to gauges. 
P = maximum pressure in tons per square inch. 
I(t = 1), I(t = 5) = time integral of pressure for the first thousandth of a second 
and for the first three thousandths of a second, in units of one ton per square inch for 
one thousandth of a second. 
Charge. Shot. D. P x W@=1) x I¢@=3) «x 
1,900 Ibs. 50/50 Amatol - | Average of 88, 90 - 46} Wirz F — 1:96 P 
92h | -85 4 1°08 - -96} 1:08 
185 — _— 47} 
1,600 Ibs. 80/20 Amatol- | Average of 85,86, 87 635 ester) 1-21 ‘i 
Paps coies se ei} 799 
1,000 Ihs. ‘P.NZT. - - | 90) = - - = Hh 1b) — “deel ae “$6 4 
| 250 a Msifigee 232 oe 
1,000 Ibs. T.N.T. - - | Average of 32,33 -| 75 — SEL) *“$6)]| 2 
" 120 7 +335 5 101 a5 Aiea 
#20 Ibs. 40/60 Amatol - | Average of 36,37 - 69 — “48 x a) ees 
11 = ont | 02 -4g{ “9! 
820 Ibs. 10/60 Amatol - | 52 - - - -| 69 = 455) ee 
| 169 = aaah 95 ‘39 f 05 
80D lhs. T.N.T. = - | Average of 17,25 -| 30 — 64 : | 27a 
50 a= 37 {1 ps -60 ( “9 
300 Ibs. 40/60 Amatol - | 29 - = = 5 50 = ey, -60 : 
120 ais = 73} 1 00 
300 Ibs. 40/60 Amatol - | Average of 105, 106, 12 4 00}, 16 
107. 28 | 1-501 8 
A0n) V-O2 a a 4 = = 
70 oy} 
(8) Surface Effects. 
When a charge is fired at moderate depth the effect observed at the surface is 
always twofold. ‘lake, for example, the case of a 300-lb. amatol charge at a depth 
of 344 feet. At the instant of firing (actually a few thousandths of a second after 
detonation) the surface above the charge begins io rise into a white dome of broken 
water, which reaches a height of about 35 feet on a diameter of 140 feet. About 
a second later the top of the dome is broken through by a rush of gas, which carries 
up plumes of spray to a height of LOO to 200 feet. The first effect signalises the 
arrival of the pressure wave at the surface ; it has nothing to do with the products of 
the explosion, in fact there is “solid’’ water between the exploded charge and the 
surface at the moment when the dome begins to form. The second effect represents 
the venting of the explosion gases. 
A large number of measurements of the dome and plumes are recorded in 
Section 26. The plumes are very variable, as might be expected; they generally 
appear as a broad bush-like eruption, but sometimes take the form of a single thin 
spout, rising to a much greater height (e.g., Shots 51 and 65). The dome measure- 
ments are more regular, and might have been even more so if it had been possible 
O AS 7498 
