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On aërial telegraph-lines this increase in the intensity of the battery occasions no particular inconvenience, other than by tending to the more rapid destruction of the small copper coils, or helices, employed; but upon submarine lines it has the effect of increasing the static electricity, or electricity of tension, which accumulates along the surface of the gutta-percha covering of the conducting-wire, in the same manner as static electricity accumulates on the surface of glass, or of a stick of sealing-wax, by rubbing it with a piece of cloth.
"Just consider, from the time the first one was laid, in 1851, between Dover and Calais, till now, about fifteen years, many thousands of miles of conducting-wire have been laid along the bottom of the sea to many parts of the world, and they are in full and successful operation at this moment.
But it is alleged that it worked slowly and with difficulty, which is true, and hence it is thought that the distance would be at least a very great obstacle. But we have shown, that, practically, by the increased size of the conducting-wire, the new cable has been reduced in length four-fifths, and will work five times as fast as the old one.
Take, for example, a schoolmaster, and suppose him to be a dynamite cartridge. His heart is a detonating cap. The schoolroom and boys form a galvanic battery. His brain may be likened to a conducting-wire. He enters the schoolroom; the chemical elements are seething in riot, books are being torn and thrown, ink spilt, etcetera.
It is overcome by increasing the number of cells in the battery, or, in other words, by increasing the intensity or force of the current. The retardation in a telegraphic cable, on the contrary, is proportional to the length of the conducting-wire and the intensity of the battery.
In the former case, by increasing the electrical force you overcome the resistance; while in the latter, by augmenting the electrical force you increase the retardation. From the foregoing law it will be seen that there are two ways of lessening the resistance upon telegraphic conductors, one by reducing the length, and the other by increasing the area of the section of the conducting-wire.
If, then, by comparison, we estimate the resistance in the old Atlantic cable to have been equal to two thousand miles of ordinary telegraph-wire, the increased size of the conducting-wire of the new cable reduces the resistance to one-fifth that distance, or four hundred miles.
In the old Atlantic cable the copper conducting-wire weighed but ninety-three pounds to the mile, while in the new cable it weighs five hundred and ten pounds to the mile, or more than five times as much.
Now, as already remarked, the copper conducting-wire in the old cable weighed but ninety-three pounds to the mile, while in the new cable it weighs five hundred and ten pounds to the mile, or more than five times as much.
By locally raising the temperature of an inconceivably fine strip of platinum serving as the conducting-wire in a circuit, the flow of electricity is impeded at that point, and the included galvanometer records a disturbance of the electrical flow.
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