628 
Gi 
potential difference developed, as registered by the cathode ray, depended 
upon the charge induced and on the total oirouit capacity. 
With high leakage resistance, the charge remained for a long time 
as indicated in the records. This long period may affect measurements of 
impulse and energy in the pressure pulse to a large and unknown degree. 
In the case of the cable under heading (5) in "Tests on other Cables", 
it was concluded that the frictional charging effects in the rubber 
composition dicleotrioc were reduced by the cloth and tape fillings either 
side of the braid. Water penetrating to the braid produced a reversal of 
the signal. 
It was concluded also from the telcothene cable results that the 
cable signal in the main was produced between the inner core dielectric and 
the braid. Consequently, it was presumed that if the braid made a more 
intimate contact with the dielectric, a marked reduction might be obtained. 
Hence, although it was not considered altogether sound to have a oable 
constructed similar to the “standard” cable but without an outer covering 
altogcther, since an outside rubber covering had worsened cable signal as 
compared to a polyvinyl chloride covering, yet on the other hand, tests had 
revealed that the cable signal was about the same with or without a P.V.C. 
covering: conscquently to save time such a sample length was manufacturod 
with a copper foil lapped underneath the braid. The result was disappointing 
although a three-fold reduction in cable signal was definite. 
This naturally led to the further consideration that if the inner 
dielectric core of the cable was covered with say aqua-dag or graphite, 
success might very well result. 
FINAL TESTS ON "STANDARD TREATED" CABLE. 
The inner telcothene core of the "standard" cable with its outer 
rubber covering was now subjected to an aqua-dag or graphite treatment; 
that is, the outer surface of the inner core in intimate contact with the 
braid was covered with this conducting layer uniformly sprayed over it. 
Tests carried out with sample lengths of oable gave very satisfactory 
cable signal reduction. These tests are still not quite completed but 
it is antioipated that they will prove to be completely satisfactory, when 
the cable is produced on a large scale. Results at present have proved 
that hand-made sample lengths have given a greater reduction (of the order 
of 3 times) than cable produced in long lengths of 250 yards for example. 
This discrepancy is being pursued and has been taken up with the 
manufacturer. But it can be statcd that at the present stage of production, 
the reduction is such that when 1 ft. of cable is subjccted to a pressure 
of 1000 1bs./in.? and the circuit capacity is maintained at 2500 wyzF, the 
voltage developed is 1 millivolt compared to 0.172 volts for the same oable 
untreated. Hand-made samples, where by inspeotion, the aqua-dag has been 
thicker and more uniformly sprayed has given a reduction to 4 millivolt 
under the same conditions, so that the rcduotion has been of the order of 
500 and 170 times respectively for the hand-made and the bulk method of 
manufacturing the "standard" treated cable. 
RE-CONSIDERATION OF THE MAGNITUDE OF CABLE SIGNAL. 
Taking the lower cable signal reduction factor of 170, for the 
three types of gauges already described, the following results are 
obtained: - 
Cable signal = 0.92 volts (under conditions already specified, 
namely 30 ft. of cable subjected to 1000 1bs./in.@ 
in a trial where 250 yards of standard cable of 
total capacity 14000 wu F is used). 
Hence cable signal now = o.88 = 0,005 volts. 
(Al) Breceierars 
