THE ELECTRIC TELEGRAPH. [From the Edinburgh Review.]

New Zealand Spectator and Cook's Strait Guardian, Volume VI, Issue 501, 22 May 1850, Page 4

THE ELECTRIC TELEGRAPH. [From the Edinburgh Review.]

Good people have perplexed themselves with speculations as to why the electricity never wanders, misses its road, or fails to find its way back. But, as has been implied already, in the case of the double wire, electricity, -like a prudent general, always takes care that a retreat be provided for, before it begins its march. Till an unbroken circuit of conductors connect the terminal plates of the battery, no electricity can be set free. It is not essential, however, that those conductors should be metallic ; a column or stratum of moist earth, we have seen, will do quite as v/ell as an iron or zinc wire. One half in length of the connecting conductors must however be insulated ; so that the electricity may be compelled to travel to the farthest point to which messages are to be telegraphed. But the other half of the conductors need not be insulated, and cannot be too large. The quicker the cuirent can pass the better ; and it will pass most quickly when conveyed by one or other of the two great electrical con-

ductors which man has at his disposal — the solid mass of the globe, and the ocean with its tributary waters. The last allusion leads us directly to the Marine Telegraph. It requires, however, no detailed description — as it differs from the Land Telegraph only in having the space between the buried plates occupied by water instead of by earth. Broad estuaries or channels do not permit the insulated wire to be carried across the bridges. The wire therefore proceeding from the copper end of the battery is embedded in gutta percha, or aDy other waterproof insulator, and sunk in the waters to a depth sufficient to secure it against fishing nets, ships, anchors, or large seaanimals. In this way it is conveyed from one shore to the other, and bending backwards after being connected with the index needles, terminates in a broad plate of metal sunk in the waves close to the further shore. A second uninsulated wire proceeds from the zinc end of the battery to a metal plate sunk below low-water mark, at the side from which the insulated wire set off. Between the immersed plates on the opposite shores, the mass of water, though ever changing, acts in relation to electricity as if it were an undisturbed gigantic metallic wire. Theoretically, there is no limit to the ocean spaces which electricity may traverse in this way. Already, accordingly, schemes for telegraphing across the Atlantic and the Pacific have been triumphantly expounded to ihe wonder-lo,ving public. One of these, whether hopeless or not, for immense distances, is so very ingenious, and so likely to succeed across limited spaces, that we cannot pass it unnoticed. It dispenses, except to a very trifling extent, with wires, and carries the current both ways through moist earth and water. It is desirable, for example, to telegraph from the right to the left bank of a broad river. From the copper end of a battery on the right bank, a wire is carried to the shore (on the same side) and soldered to a plate buried in the river below water mark. A wire is also led from the zinc end to a long coil of wire which ends in a metallic plate. This likewise is buried in the river below water mark on the same right bank — but a distance from the battery, " considerably greater than the breadth of the river across which signals are to be sent." On the left bank two plates are immersed opposite those on the right bank, and connected by a wire. The electricity on leaving the battery has therefore the choice of two paths. It may either keep entirely on the light bank passing from the one buried plate on that side to the other, and so back to the battery by the long coiled wire. Or it may cross to the left bank through the water, traverse the wire on that side, return across the water to the right bank, * and regain the battery by the shorter coiled wire. The Thames, as we learn, has been actually crossed by electric currents in this way ; the resistance to their passage by the water between the banks being less than that between the ends of the wires on the right and left banks respectively. A wire stretched from the Land's End to John O'Groat's House, would indeed measure but a small portion of the breadth of the Atlantic, — but by twisting the wire into coils, we might include in a short space an enormous leugth.