Page:Ballantyne--The Battery and the Boiler.djvu/75

 wires all breaking at the same spot was so remote as to be almost impossible, and if even one wire out of the seven held, the continuity would remain. Nay, even all the seven might break, but, so long as they did not all break at the same place, continuity would not be lost, because copper would still continue to touch copper all throughout the cable's length.

In the process of construction, the central wire of the copper core was first covered with a semi-liquid coating of gutta-percha, mixed with tar—known as "Chatterton's Compound." This was laid on so thick that when the other wires were wound round it all air was excluded. Then a coating of the same compound was laid over the finished conductor, and thus the core was solidified. Next, the core was surrounded with a coating of the purest gutta-percha—a splendid non-conductor, impervious to water—which, when pressed to it, while in a plastic state, formed the first insulator or tube to the core. Over this tube was laid a thin coat of Chatterton's Compound for the purpose of closing up any small flaws or minute holes that might have escaped detection. Then came a second coating of gutta-percha, followed by another coating of compound, and so on alternately until four coats of compound and four of gutta-percha had been laid on.