813 
aoe 
If L = 750 feet, P = 1000 lbs./in® 
then Vp 2 ply = 0-278 volts. 
2. CABLE SIGNAL. 
The ratio Cable Signal/Gauge Signal:- 
Let cable signal per foot of cable per lb. /in? pressure per foot 
length of cable in circuit = v volts. 
Then cable signal per foot of cable per 1b./in2 pressure per L feet 
of cable in circuit = op SEE 
And cable signal per foot of cable per P lbs ./in2 pressure per L feet 
of cable in circuit = a volts, 
If 1 foot of this cable is immersed in the water and subjected to tl} - 
same pressure as thg miniature gauge, then the cable signal per 1_foot of 
cable per P lbs,/in“ pressure per L feet of cable in circuit = 1 volts. 
Hence percentage ratio, 
Cable signal $Pvi 0.0822 nA P 
Ol Ue ae aia At ee L =, 100% 
4216 ee 
EXAMPLE : - 
For a two-ply miniature gauge $" in diameter, assume that a trial is 
carried out Where pressure measurements are required involving 30 feet of 
the cable immersed completely in water and therefore subjected to the same 
pressure as the gauge from the underwater explosion, 
oo i 44.380 Vv y 
Now, with the special cable, experiment has shown that when 1 foot of 
the cable is subjected to a pressure of 1000 1bs./in2 pressure in a circuit 
capacity of 2500 micromicrofarad (135 feet), the voltage developed is 
certainly less than 4 of a millivolt, but taking this figure as an upper 
maximum, 
; 
then vy = SHOX 15 _ 45x 10° 
Streastes 44.380 x 45 x 4076 qs 
= 0.657%, 
As described in the body of the report, firing against ‘the cable has 
confirmed the fact that cable signal is not significant. 
3. OSCILLATIONS IN TOURMALINE DISCS FROM SHOCK EXCITATION. 
Various complex modes of vibrations may be set up in crystal discs 
of tourmaline when these are subjected to underwater explosions. It is very 
probable that with the present miniature gauge ditrected edge-on to the 
pressure wave, the pressure-time signature registered by the cathode ray 
oscillograph is so faithful that only resonant vibrations of the crystal 
slices remain superimposed on the pressure pulsc. This is particularly 
noticeable in the case of the 1" diameter gauge where about 4 oscillations 
appear on the slope of the wave front (complete period 16 microseconds), 
paving thercfore a frequency of oscillation of 250,000 o/s. Moreover, if 
he wave-length is assumed to be equal to the disc diameter, the frequenoy 
calculated is approximatcly in agreement with the observed frequency, assuming 
sound velocity for tourmaline to be 6000 meters per second. 
