1214 
-ye- 
APPENDIX 
THE MECHANISM AND TIMING OF THE MULTIPLE PULSE EFFECT 
BY SYMPATHETIC DETONATION 
An attemot is made below tc oescribe now the multiple pulse effect Is obtained by 
symcathetic detanation. 
Assume that the ¢harge X (sce late 1, Figure 1) Jetonates instantaneously. The 
‘rays* of the oressure oulse travel radially outwards from the charje through the water at a 
velocity yrsater than 5,000 ft. 2=r second, and strike the charge Y along the 1ine L M, ana, 
until detonation, travel through that charge with the velocity of souna through T.N.T. (about 
6,000 ft. 2er second — sce Wood, S.S. Recort Nc. 1064). at some time t, after the rays 
arrive at LM the charge Y is detonated symoatnetically. Curing detonation the detonation 
wave travels from the coint of initiation in all directions through the charge at apcroximately 
20,000 ft. over second (the velocity of detonation for T,N.T.)» On reaching the far slae of 
charje Y at (® Q) the pulse then travels through the water with a velocity whieh soon drops to 
aporoximately 5,000 ft. oer second. 
Two culses therefore arrive at gauge C, one from X diffracted round the charge Y, which 
travels through the water at 5,000 ft. cer second (aporoximately) and the other originating from 
Y t seconds after the X culse arrives at L M, which travels to the © Q side of Y¥ at 20,000 ft. 
per second, ang then travels through the water at a velocity soon falling to 5,000 ft. cer second. 
Consider the times of arrival of the two oulses at C. That due to the charge Y nas, 
as comoared with that due to X, a lag t seconds ana gains (1) due to the detonation wave 
travelling at 20,000 ft. ser second through part of the charge Y (as compared with 5,000 ft. 
per second) (2) due to the voint of initiation cf the charge Y not veing at the sage of the 
Charge, along L M, but at some coint in the Interior cf the charge. 
If the 129 t, is equal to the sum of the gains the two culses arrive at ¢ simultaneously. 
As discussed in the recort tne cifference between tne lay t, and the two gains Is of the order 
of 75 microseconds. 
Gauje A recoraed the multicle oulses secarately (see >late 3, Figure 5). The time lag 
between the arrival of the peaks was always slightly more tnan is accounted for by the pulse 
travelling at 5,000 ft. per second from X tc the cage of Y (at LM) and back to the point in 
space which was originally the centre of the charge X. The extra time ts not necessarily the 
time lag t, between the arrival of the pulse at L M ana the sympathetic detonation, because 
the return culse arrives at the Gauge A after travelling through the gas bubble from X and the 
velocity cf the pulse on the return path may drop below 5,0 ft. cer second In passing through 
the gas bubbls, 
