Note A — Chapter XVI · VICTORY AT LAST.
Reading edition
The new method is thus explained by Mr. Deane:
"The fundamental difference between last year's system of testing and that of the present expedition is, that now all the ordinary tests for continuity may be made simultaneously with the test for insulation, which is not interrupted at all; whereas, last year, during half the time spent in laying the cable, the insulation test was wholly neglected.
"Last year, each hour was divided into four parts. The first half of the hour was spent in testing for insulation. During the second half, which was divided into three periods of ten minutes each, tests were made to ascertain the resistance of the conductor and to prove the continuity of the same. All these tests were of such a nature as to afford no criterion whatever of the state of the insulation during their continuance, so that during the half of each hour, or, in other words, during half the time spent in laying the cable, the insulation test was neglected. Also, while the insulation test was being made, there was no means of communicating with the shore, as the observations were taken on board only. This year, a test for insulation is constantly kept on, and, by Mr. Willoughby Smith's arrangement, corresponding observations are made both on ship and shore. At stated times during the hour, the continuity test is made at the shore station by means of a condenser applied to the conductor of the cable. The effect of this is to increase the deflection on the ship's insulation galvanometer, thus serving as a continuity test. Communications from shore to ship are also made by these means. The ship can send signals to the shore by simply reversing the current for certain lengths of time, answering to some understood code, or by increasing and diminishing the tension of the line, according to a preärranged plan. All these operations may be performed without interrupting the insulation test, except for a few seconds while the current is being reversed. So far for the new system in the electrical room as compared with last year."