640 Original Articles. | Oct., 
On a careful inspection of the above summary, it will be seen that 
a great difference exists in the retentive powers of the different imsu- 
lators under severe pressure: these anomalies almost defy attempts at 
comparison. If we take No. 1, the Gibraltar core, cured by Mackintosh, 
we have, after an immersion of 282 hours, at the enormous pressure of 
10,000 Ibs. per square inch, a power of retention of 136 minutes; at 
325 hours’ immersion, it is reduced to 100 minutes; and at 405 hours’, 
it is still further reduced to 32 minutes, showing that the insulation 
is very considerably affected when a sufficiently long period of time is 
allowed for the permeation of the cable. In the next series of experi- 
ments, on a core impregnated with an insulating liquid, we have 
totally different results, as there is a steady and progressive gain in 
the insulating powers of the core. At 24 hours of immersion, we have 
11 minutes 40 seconds; at 48 hours, 27 minutes 25 seconds; and so 
on till, at 170 hours, the charge is retained for a period of 105 minutes. 
Wray’s core was too small to be fixed in the cylinder ; but it retained 
a charge under atmospheric pressure for 1,300 minutes, and hence 
manifested a superiority to all the other cables tried. In another trial 
with a larger cable, this insulator also gave very satisfactory results. 
In No.5 core, of twenty alternate coats of gutta-percha and Chatterton’s 
compound, there are the variable results of an increase in the first five 
experiments from 43 minutes in 121 hours to 118 minutes in 150 
hours; whilst in the sixth experiment, the retention after 170 hours’ 
immersion again falls to 100 minutes. These discrepancies are diffi- 
cult to account for, and a more lengthened series of experiments is 
required for the attainment of accurate results. No. 6, a core of pure 
india-rubber, indicated very good insulation before the pressure was 
apphed; but after 80 hours’ immersion the insulation was almost 
entirely destroyed. 
The very important question of insulation in deeply-submerged 
cables is far from*having received, as yet, a complete solution. The 
foregoing experiments are satisfactory, in so far as they show approxi- 
mately the relative porosity of various materials; but they do not 
point out how we are to obtain an insulator impermeable to water, and 
at the same time a good non-conductor. This desideratum has yet to 
be attained. 
We might have extended our illustrations on the permeability, effects 
of temperature, and other conditions connected with the insulators now 
in use; but having already enlarged the article considerably beyond 
the usual limits, we must conclude with observing, that in the second 
attempt to ensure success, as regards both the manufacture and laying 
of the cable, a second serics of elaborate experiments had been insti- 
tuted, under the direction of a scientific committee appointed for that 
purpose. The results of the experiments are satisfactory and interest- 
ing, but we must reserve them for a future notice, at a time when the 
manufacture is further advanced, and when we may confidently hope 
that the efforts now making on the part of the directors of the Atlantic 
cable will be crowned with success. 
In the meantime, let us present our readers with drawings and 
particulars of the two cables, showing that which failed in 1858, and 
