801 
= 5a 
(a) The first miniature tyo-ply gauge. 
This gauge had two tourmaline disos $" in diameter and 4" thick, a 
central stecl electrode 0.013" thick and outer stecl electrodes 1/16" thick, 
-comented with "gelva" to the crystal faces. The insulating layer was 
telcothene enveloping the gauge itself and connected to that surrounding 
the cable braid. Threc layers of good quality rubber tape served as a 
further protcotive outer covering and this was joined to the rubber 
covering of the cable. 
(b) Results of first shots against two-ply gauge. 
The charges used for the first experimental tests were 14 1b. blocks 
of T.N.T. in standard cases. No attempt was made initially to orientate 
the gauge, and although there was similarity between some of the pressure- 
time records, the variations were considerable both in form and amplitude. 
Later, therefore, thc gauge was orientated towards the pressure wave, and 
this resulted in omsistent records being obtained with the gauge cdge-on, 
and face=on respectively, but the types of records in the two directions 
differed considerably from each other, 
Plate 2, Records 1 and 2, respectively show typical face-on and 
edge-on records with a sinusoidal 100 microsecond time base, Reoord 1 
(face-on) has two peaks about 23 microseconds apart but the significance 
of this is not clear, and the spurious frequencies associated with both 
Signatures mar the theoretical condenser discharge type of pressure=time 
signal normally associated with an underwater explosion. The time of rise 
of the facc-on pressure pulse is slightly shorter than for the edge-on 
condition. Had the records been faithful ones, this feature would have 
been more pronounced, as will be showm later. 
(co) A single crystal gauge. 
This was of similar construction to the two-ply described briefly in 
paragraph (a) above, the two electrodes being of steel 1/16" thick. 
(ad) Results with singlo crystal gauge 
Plate 2, Records 3 and 4 show face-on and edge-on records. These, 
except for minute details are very similar to the results discussed in 
paragraph (b) above, I+ was concluded that whatever the explanation for 
the curious form of the pressure-time signatures, in general the single-ply 
and two=ply gauges behaved with remarkable similarity, but for fundamental 
exploration, it was decided to continue firing against a single crystal gauge. 
(c) Single crystal gauge with thin olcgtrodes. 
The construction remained the same as indicated in paragraphs (a) 
and (0), except that tinfoil 0,001" thick was used as eleotrodes. 
(f) Results with the thin electrode single crystal gauge. 
Plate 2, Records 5 and 6 are typical reoords for face-on and edge-on 
positions. There is still a tendency for the facc-on record to show a 
double peak. The signatures are considcrably oleaner, however, but the 
times of rise of the wave front are considerable. Moreover there was a 
difference (records not shown) between the recorded signaturcs for the 
opposite faces and edges. 
It was noted also that the pressurc amplitudes were considerably 
less than for the thick stcel clectrode single orystal under approximately 
Similar firing conditions. 
; This gauge was reconstructed and only one layer of rubber used as 
the outer insulating cover. The records (not shown) were differcnt, but 
not to a vcry marked degree. The inner insulation layer wes still 
telcothenc .«.+.- 
