OF ELECTEIC SIGNALS THEOIJGH SUBMAEINE CABLES. 
1001 
negative electrification, and that a great part of the observed change was completed 
before the end of the first minute after the cable was connected with the battery. This 
gradual improvement of insulation would gradually increase the received current long 
after all inductive phenomena had ceased. For instance, the resistance of the total 
gutta-percha sheath of 2192 knots at 60°, after negative electrification for about 15", 
would be 104x10^® absolute British units; after one minute, this resistance would 
increase to 132 x 10'“. The resistance of the conductor was about 55 x 10'“. 
If the insulation had remained constant at the first-named figure, the final maximum 
arriving current would have been only 78‘4 per cent.* of the entering current; and if 
the insulation-resistance had remained constant at the second figure, the final arriving 
current would have been 82 ’4 per cent, of the entering current. It is not therefore 
surprising that the observed curve, subject to the infiuence of imperfect and varying insu- 
lation, should not more perfectly coincide with the theoretical curve, in which perfect and 
constant insulation is assumed. When allowance is made for the change in the enter- 
ing current due to the change in the total resistance of the circuit caused by the change 
in the insulation-resistance from 104x10'“ to 132x10'“, the final arriving current with 
the lower insulation would by calculation be about 97 per cent, of the arriving current 
with the higher insulation, and this proportion very exactly corresponds with the slow 
increase observed during the last forty seconds of the minute. This increase has there- 
fore no connexion whatever with the retardation properly so called. 
The identity of the curve of increase with the curve of decrease seems to show that the 
apparent increase of the resistance of the gutta percha is rather due to an absorption 
of electricity which is again given out, than to a real change in the conductivity of the 
material f . 
The effect of varying insulation would be much less felt during the actual trans- 
mission of signals, for then the greater part of the cable is constantly electrified in one 
manner, and the resistance of the gutta percha under such circumstances remains 
sensibly constant ; we might therefore here expect a better agreement between theory 
and observation. 
In order to examine the results of the experiments on repeated signals, the number 
of dots sent per minute, and the corresponding amplitude of oscillation observed in the 
received current, might be used respectively as abscissae and ordinates, to give a curve 
expressing the rate at which, for each length of cable, the effect of the signals dimi- 
nished as their speed increased ; but, by the mathematical theory, the time required for 
any electrical operation varies as the square of the length of the cable. The product of 
the square of the length into the number of dots producing a given amplitude of varia- 
tion should therefore be constant for all lengths of the same cable ; and by using this 
product as an abscissa, instead of the simple number of dots, one curve should give the 
* Appendix, Section I. 
t The truth of this conclusion has been established by the results of some experiments on the Malta- 
Alexandria cable, made by Dr. Esselbach, and received by the author since writing the above. 
