498 
RESULTS OF THE EXPERIMENTS. 
The object of the experiments, it has been stated above, was to express, if possible, the under- 
water pressure-time curve to an explosion in terms of certain distances, weights, etc., which could 
easily be measured or assumed. Many pressure-time curves have now been completely determined by the 
methods described in the report, but, from the point of view of expressing the damaging capacity of an 
explosion, it has been found easier to speak of the numerical values of the maximum pressure, momentum 
and energy of the pressure-train, and of the times taken for the pressure to rise to its maximum and to 
die away, rather than of the somewhat cumbersome mathematical formulae which can be used to express the 
shape of the pressure-time curve. The five quantities, maximum pressure, momentum, energy and times of 
rise and fall of pressure, have some clear relations with damaging power, while the equation of the pressure- 
time curve has no obvious interpretation in terms of damage, nor has it yet been found possible to refer 
any given amount of damage definitely to the numerical factors which determine mathematically the shape 
cf the pressure time curve. 
Shape of the pressure Time Curve, 
In general, the pressure-time curves due to under-water explosions show a rapid rise of pressure 
to a maximum value, followed by a fall lasting about twenty times as long. These times are Clearly 
related to the rate of growth and collapse of the bubble of hot gases produced in the water by the explosion, 
and the results of experiments are in good agreement with a theoretical investigation which has been made 
into the movements of the surface of the bubble. The time taken for the pressure to rise to its maximum, 
and the maximum pressure reached, may be modified by the presence of air in the case containing the charge, 
the mechanical properties of the case, and the method of initiating the explosion. The average time of 
rise of pressure for al) charges of the high explosives tested of weights between 24 and 1000 lbs. is about 
five hundred—thousandths of a second, and the average time of fall is about one thousandth of a second. 
Measurements of the time taken for the pressure to fall to a definite fraction of its maximum 
value indicate that this time is approximately proportional to the linear dimensions of the charge, i.e. 
to w4, The shape of the curve is often seriously irregular and the departures from smoothness have been 
traced to irregularities in the charge and its case, and to bodies in the neighbourhood which may reflect 
or absorb the pressures in the water. 
The relations between maximum pressure, momentum and energy, and weight of explosive 
and distance 
The mean of a large series of observations made with charges whose weights varied between 24 Ibs. 
and 2000 1bs. may be expressed as follows - 
(1) Maximum w° 38 : 
pressure = 12000 D lbs. per sq. in. 
+65 
1.90 x lbs. secs. per sq. in. 
(3) Total Energy = 3.5 x 10 
of the 
spherical 
wave due to 
an explosion 
under water 
(2) | Momentum 
5 wy ft. Ibs. 
or Energy per 
sq. ft. of wave 
front ata 4 oW 
dletancelo =) 22799 x00 32 ft. Ibs. 
from origin 
where WwW = weight of charge in lbs. 
D0 = distance, in feet between the centre of charge and the point at which the pressures 
are measured. 
These wo oe 
