1058 
Results. 
Typical pressure-time records obtained in the tests are reproduced in Figure 3(a), (b), 
(c), (d) and (e). It is seen that the records consist of a main pulse followed about 2 milliseconds 
later by reflections from the bottom and the sloping sides of the tank. The two lower records show 
further waves wich occur 5 to 6 milliseconds after the Initial wave. The origin of these waves 
is not known but they may be due to the bubble produced by the charge. The pulses were probably 
too small to be detected in the other records. 
The main pulses in Figures 3(a), (b) and (c) are similar to those produced by a charge of 
normal shape, i.e. a cylindrical charye with height equal to diameter and have a shock front followed 
by a rapid decrease of pressure behind the front. In Figures 3(d) and (e), however, the rate of fall 
of pressure is much lower. 
The variation of peak pressure and impulse with distance along the perpendicular bisector of 
the line charge are shown in Figures 4 and 5 for lengths of 30 feet, 14 feet and 5 feet of Cordtex. 
These figures 21so show the values for a 1 oz. Charge of P.E.T.N. Of normal shape. It is seen that 
in these tests the length of Cordtex did not appreciably affect the peak pressure at a given distance 
from it but that the impulse decreased with decreasing length of charge. 
The velocity of detonation along the Cordtex is about 20,000 ft./sec. whilst the velocity of 
sound in water is only about 5,000 ft./sec. Hence the pressure-wave front in the water will resemble 
somewhat the bow wave produced by firing a bullet in air. The state of affairs will be approximately 
aS represented in Figure 2 where sin. M equals 0.25. The first part of the pressure wave to reach 
a point at a perpendicular distance d from the middle of the line charge thus comes from a point 
at a distance x from the centre of the Cordtex where x = 0.260 approximately. For the lengths of 
Cordtex and the distances d used in the tests, x was less than half the length of the charge and it 
is therefore to be expected that the initial peak pressure will be independent of the length of the 
charge. This acoustic approximation is not strictly true for explosion waves but serves to indicate 
the nature of the effects involved. Since the tail of the wave is due to the cumulative cffect 
of all the wavelets produced by al) parts of the Cordtex, the impulse will decrease with length of 
Charge, aS was in fact observed. 
The pressure and impulse values at points on the perpendicular bisector of the 1u fect 
Charge were about the same as those from 1 oz. P,£.T.N, at equal distances from the centres of the 
charges. Thus at these points 1.63 0z. P.E.T.N in Cordtex is about equivalent to 1 oz. P.E.T.N. 
in a charge of normal shape. 
in Figures 6 and 7 the variations of pressure and impulse at points round 5 feet of Cordtex 
are shown as functions of the shortest distance from the charge. It is seen that the pressure was 
greatest on the perpendicular bisector of the lime charge and least on the axis when detonation was 
towards the gauge. The difference in peak pressure at points on the axis of the charge may have 
been due to the contribution of the detonator which contained about 1 gm. charge since the pressure 
was greater wnen the detonator was near the charge. This is indicated by the pressure-time curves 
(Figures 3(d) and (~)) where the initial peak pressure falls rapidly to about the same value in 
each case. 
Figure 7 shows that under the test conditions at points at the same distance from the charge, 
the impulses along the axis of the charge were independent of the direction of detonation and were 
about half those on the perpendicular bisector. Reflection from the free surface, however, reduces 
the impulse along the axis. Figure 3(c) shows that perpendicular to the line charge the pressure— 
time curve is not appreciably affected by the surface reflection and the measured impulse Is 
approximately the total impulse. On the axis of the charge where the rate of decay of pressure 
behind the shock front was less rapid, Figures 3(d) and (e) show that the negative surface reflection 
Cuts off an appreciable part of the tail of the pulse. Consequently the measured impulse was 
probably considerably less than the total impulse produced by the charge in the water. 
