802 
Sikes 
telcothene. The inference was that not only thickness of insulation, but 
thickness and material of electrodes had an effect on the pressure-time 
Signatures. 
(g) Original two-ply gauge with tinfoil eleotrodes. 
The construction remained as hitherto except that the outer steel 
electrodes 1/16" thick were replaced by tinfoil 0.001" thick. 
(h) Results with the two-ply gauge, having tinfoil outer 
eleotrodes. 
Plate 3, Records 1a and 1b, 2a and 2b, were obtained with the gauge 
face=-on (two opposite faces) and edge-on (two opposite edges) respootively. 
As pointcd out under paragraph (f), tho records for the two opposite faces 
are not identical nor are thoy identical for the two opposite edges. This 
can be acoounted for partly by the fact that the gauge was not truly 
face=-on nor truly edge-on in any one position, but as proved later, this 
is not the complete explanation. 
It can be seen that with the two-ply gauge, the records obtained aro 
cleaner than when thick stccl outor electrodes aro used. Moreover thoro 
is again confirmation that the amplitudes are less with thin tinfoil 
electrodes. The double peak has still a tendoncy to remain when the 
gauge is face-on to the pressure wave; and the wave front is less stcep 
than expected. 
(i) Single orystal with thin spring steel cleotrodes. 
The construction remained as hitherto, except that the two elcctrodes 
wore made from spring stccl 0.0015" thick. 
(Jj) Results with singlo orystal gauge, having stocl foil 
oleotrodos. 
The records obtainod aro showm on Plate 3, Reoords 3 and 4 with 
the gauge face=-on and edge-on rospectively with respect to the pressure 
wave. Rocords (not shown) wore again somewhat different for the opposite 
face and cdge. 
(k) Alterations in amplifier. 
During the above mentioned series of tests considerable temporary 
alterations were made to the amplifier used with a view to ascertaining 
the oause of the curious signatures recorded. These comprised changes 
in cable termination such as the shorting out of the inserted resistance 
equal in value to the surge impedance, the shorting out of the grid- 
inductance which reducod the flat responso of the amplifier at the higher 
frequenoy range from 550,000 o/s to about 200,000 o/s. The conclusion 
reachod was that tho amplifior did not account for the distortions in 
the recorded pressure=timo pulso. 
(1) Firing against tho ocablo. 
A singlo orystal gaugo was comploted in the normal manner except 
that its oleotrodos were disconnooted frem the oable conductors. Two 
charges ‘ore firod against tho cable with the olrouit as normally 
connected to the amplifior and cathode ray tube. No movoment of the 
cathode ray spot was obtained. This provod that the oable was froe from 
pick-up duo to prossuro ohanges in the wator. 
(m) Iwo-ply gauge with three steel foil eleotrodes. 
The construction was standard except that the three electrodes were 
made from spring steel 0.0015" thick. 
(n)) ciicie's 
