808 
=w1On= 
The face-on record shows the overshoot, accompanied by the almost 
instantaneous time of rise, whereas the time of rise in the case of the 
edge-on record is of the order of 16 microseconds. 
On all edge-on records oscillations are apparent on the sloping time 
of rise, and when, as in the case of the 1" gauge, this time is relatively 
long the film speed makes them more pronounced. [These are the natural 
oscillations set up in the tourmaline orystal, and their frequenoies are 
dependent on the size of the gauge itsclf. In the case of the 1" crystal 
gauge the osoillations have frequencies of approximately 240,000 .c/s. 
They are referred to here for the first time in this report, but of-vourse 
close examination of the records obtained with the $" and 4" diameter 
gauges reveal similar oscillations in edge-on positions. The smaller 
the diameter of the gauges, the higher these frequencies become, tho 
further reference to then appears in Appendix 1. 
On Plate 11, Record 3, is exhibited the pressure-time pulses 
obtained from the 1" gauge with its crystal faces parallel to the water 
surface and the cable leading away from the pressure wave front. Plate 11, 
Records 4, 5 ond 6 show similar pressure~time signatures with the orystal 
faces perpendicular to the water,surface, Record 4 in the oase of the 
44 1b. T.N.T. charge in its standard canister, Record 5 for a bare 14 1b. 
T.N.T. charge, and Record 6 for a 14 oa. spherical bare P,E. charge without 
@ primer. It will be seen that there are oscillations similar to those 
mentioned above, a finite time of rise of the pressure wave (46 microseconds) 
and that smoother contours are obtained with the bare charges, particularly 
the spherical types. 
When the high frequency response of the amplifier was cut down from 
about 500,000 c/s to about 1/10th of this value, the sharp peak was rounded 
off and the amplitude reduced by about 20/. 
EXPERIMENTAL WORK: PART 6. 
This work constitutes the records finally obtained with the newly 
designed 3" gauge, both single-ply and twin-ply. The method of construction 
of twin-ply gauges was being developed simultaneously with this experimental 
work. This is described in Appendix 2. Here, there is only need to 
mention that the central electrode of silver foil only 0-0025" thick is 
strictly comparable with the burnished silver paste sintered and baked onto 
the outer crystal faces. Flat ligaments of annealed copper are soldered 
onto the outer silver films but the central electrode of silver foil is so 
cut as to provide its own silver tag for soldering onto the central core 
of the cable. 
(a) The single-ply 4" gauge. 
The construction is on similar lines to that given in Appendix 2, 
the thickness of crystal being 1/16". 
(b) Results with the 3" single crystal gauge. 
It was not considered necessary to repeat the normal face-on and 
edge-on records. Shots were fired therefore with the gauge having its faces 
parallel and perpendicular respectively to the water surface and the cable 
attached to the gauge leading away from the pressure front - these are 
edge-on records with the cable having its effect in distorting the pressure 
field reduced to its symmetric minimun. 
On Plate 12, Records 1 and 2, are shown pressure-time records for @ 
standard 1: 1b. T.N,T. charge and for a 14 oz. P»E. spherical bare charge 
respectively, with the gauge having its faces parallel to the water surface. 
On Plate 12, Records 3, 4. and 5, pressure time pulses are exhibited for a 
standard 14 1b. 1.N.T. charge in its standard case, for a 14 1b. T.N.T. 
bare charge and for a spherical charge respectively, the gauge having its 
faces perpendicular to the water surface. The times of initial pressure 
TISe eocece 
