7 , 91 
explosion of | lb. of 40/60 amatol is roughly 10° foot-pounds, it appears that about 3 
quarter of the whole energy of the explosion gets away in the pressure wave. 
(5) Regularity and Symmetry of the Pressure Wave. 
A mass of evidence was collected showing that the pressure wfive from a high- 
explosive charge under water is very regular and symmetrical; the pressure wave 
springs away from the charge with practically the same strength in all directions, and 
when similar charges are fired under similar conditious the results are nearly 
identical. 
The time-pressure curves illustrating this report represent in most cases the 
average of several shots. In only one instance (referred to in Section 10) did the 
results of any individual shot differ by more than about 5 per cent. from the group 
average. Three typical groups are shown in the following table, and some other 
figures are given at the end of Section 18. 
TaB_e I. 
D = distance in feet from centre of charge to gauges. 
P = maximum pressure, in tons per square inch. 
I (t = 3) = time integral of pressure for the first three thousandths of a second, 
in units of 1 ton per square inch for one thousandth of a second. 
Charge. Shot. D. 
1,600 Ibs. 80/20 amatol =- = - | 85 634 
86 
87 
Average. 
272 lbs. R.D. No. 30 mixture - ~— - 69 50 
71 
94 
Average. 
312 Ibs. guneotton = - - - 2 60 50 
63 
67 
Average. 
The symmetry of the pressure wave was tested, in a very large number of shots, 
by comparing the indications of two groups of gauges at equal distances from the 
charge in opposite directions, one group on the side away from the “ Malapert,” the 
other on the near side, and in some cases a third group of gauges was hung at an 
equal distance vertically underneath the charge. The ratios of the results in these 
three directions are shown in Table II. When copper gauges were not available for 
this purpose, use was made of the plasticine gauges described in Section 20. The 
distance of the gauges from the charge was in nearly all cases 50 feet from a 300-lb. 
charge and corresponding distances (Section ¥) from other charges. It will be seen 
that there was only one instance of pronounced dissymmetry (Shot 27); in all other 
cases the differences are slight, averaging only about 5 per cent. Considering that 
the differences recorded in the table must be partly due to errors of the gauges and 
inexactness of the measured distances it is clear that the strength of the pressure wave 
is generally very nearly the same in all directions. 
The.special case cf a charge of very elongated shape is dealt with in Section 15. 
