805 
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(a) Alteration in gauge thickness. 
The investigation was continued with the single-ply gauge 4" in 
diameter, and 4" thick, and in addition with single-ply gauge of thioxmesses 
$" and 4/16" 
(b) Single=-ply gauge with copper electrodes and wax-paraffin 
insulation layer. 
For all three thicknesses of gauges, the electrodes consisted of 
the annealed copper foil 0,022" thick as used recently, the insulator being 
a thin layer of the paraffin wax-vaseline mixture. 
(c) Results of single-ply gauges, having wax=paraffin insulation. 
For comparison with previous rocords shown in this report, typical 
reoords are given only for the pressure pulse signatures obtained with the 
4" thick gauge. Those are showm on Plate 7, Records 1, 2, 3 and 4. 
Records 1 and 2 were obtained with the gauge face-on and edge-on to the 
pressure wave respcotively whereas in Records 3 and 4, the gauge had its 
faces parallel and perpendicular respectively to the water surface. 
It will be observed that in Record 1, there is an overshoot and that 
the time of rise is certainly of the order of a microsecond. ‘/hereas, 
with the remaining records, although Record 2 is slightly different in 
form from Records 3 and 4, the times of rise of the wave fronts have been 
Measured and found to be about 8 microseconds, which is the time that the 
pressure wave takes to traverse the diameter of the gauge. In Record 1, 
the overshoot is due to the fact that the gauge was rigidly held, the 
tendency being to record a peak pressure double that of the incident Wave. 
When the gauge is held face-on in a scmi-rigid manner to the pressure wave, 
some intermediate but indcterminate value between the peak pressure and 
double the peak pressure value of the explosive wave would be expected. 
Therefore whilst a thin gauge held face-on to the pressure wave would be 
advantageous in giving extremely sharp times of rise provided the amplifier 
and recording film is capable of following and resolving the signatures, 
the better arrangement is to hold the gauge edge-on to the wave and 
preferably perpendicular to the water surface with the cable leading away 
in the direction of the motion of the pressure wavc. Allowance has to be 
made for the effect of the reduction in peak pressure; this is brought 
about by averaging the pressure over the size of gauge. For a 3" gauge, 
it amounts to a 34 reduction in peak pressure. 
On the whole it was found that the same features were exhibited with 
the thinner gauges. 
(a) Gauges with sintered silver elcotrodes. 
The method of sintering silver onto the orystal faces is desoribed 
in Appendix 2 of this report. The silver is estimated to be only 0.0025" 
thick. The insulation is still a layer of paraffin wax-vaseline mixture. 
Three such gauges of thicknesses 4", 4" and 1/16" respeotively were tested. 
(ec) Results with single-ply gauges, having silver eleotrodes and 
Wax-vasoling insulation. 
The conneotion between the electrodes and the cable leads was made 
by soldering annealed copper strips 4" long to the silver film. The 
reoords obtained are not given but in the main they are almost identical 
to those shown in Plate 7. It would appear therefore that sintering 
silver electrodes onto the crystal faces is not greatly superior to cementing 
metal foil clactrodes of copper, although it is known that cementing metal 
peat os steel with gelva is not mechanically satisfactory for long 
Ons. 
(eyes 
