Heroes of the Telegraph/Chapter 4 > 자유게시판

The result of this phenomenon is, that messages sent over one wire are liable to be received on all of the other wires, and, in the case of the telephone, this phenomenon is noticeable on cables one thousand feet long, and on a cable one mile long the parties on one wire can easily understand what those on the other wires are saying. The Meyer-Baudot and the Quadruple receive four messages at once and record them separately; while the harmonic telegraph of Elisha Gray can receive as many as eight simultaneously, by means of notes excited by the current in eight separate tuning forks. It consists of a very long fine coil of silk-covered copper wire, and in the heart of the coil, within a little air-chamber, a small round mirror, having four tiny magnets cemented to its back, is hung, by a single fibre of floss silk no thicker than a spider's line. 1. If an electric conductor be brought near to a large mass of conducting matter, as is a wire when it is taken down from a pole and buried in the earth, there appears in the current the phenomenon of retardation, by which each signal, instead of being sharp and distinct, is partly kept back, so that it overlaps and mingles with the next; the result is to limit the speed of working of the apparatus; or if, like the telephone, it be an apparatus in which the currents are necessarily extremely frequent, to confuse and destroy the signals altogether.

Strong head winds kept the Agamemnon back, and two American ships which got into her course had to be warned off by firing guns. Next morning a grand salute of 100 guns resounded in New York, the streets were decorated with flags, the bells of the churches rung, and at night the city was illuminated. It must be remembered, however, that these various systems have cost from ten to twenty times as much as similar overhead lines; that, for every mile of under-ground wire, there are many miles on poles; and that in Paris, which is the only city in the world having a complete under-ground system, there are unusual facilities for the running of wires, as sewers large enough to walk about in extend even under the less important streets of the city. In Vienna, Prague, Brünn, Munich, Augsburg, Nuremberg, and many other cities, the telegraph-wires are carried under-ground by armored cables to the outside of the city. With ordinary Morse telegraphic apparatus, what is electric cable this is not very troublesome on under-ground lines a hundred miles long. Professor Morse and De Sauty, the electricians, failed to restore the communication, and the engineers were preparing to cut the cable, when quite as suddenly the signals returned, and every face grew bright.

In 1855 the French government, having failed in their attempt to use gutta-percha wires, laid down a large number of bare wires in a trench filled in with bituminous compounds. If the signals on one wire of such a cable be sharp and quick, they cause fac-simile signals on all of the neighboring wires, and this too, though the insulation may be absolutely perfect; indeed, above a certain point, the more perfect the insulation the greater the induction. In 1853 the Telegraph Company of England laid down a cable of ten gutta-percha-covered wires, in wooden troughs, along the high-road between London and Manchester, a distance of two hundred miles. He was joined by E. O. Whitehouse in these researches, and when later he was appointed engineer to the Atlantic Cable Company, Whitehouse became electrician to the company. During the same year the Electric Telegraph Company laid down a somewhat similar system between London, Manchester, and Liverpool, though iron and earthenware pipes were substituted for the wooden troughs. The submarine hill, with its dangerous slope, was passed in safety, and the 'telegraph plateau,' nearly two miles deep, was reached, when suddenly the signals from Ireland, which told that the conductor was intact, stopped altogether.

The present complete system, as used between Liverpool and Manchester, was constructed as follows: Iron or stoneware pipes were laid from one to two feet below the level of the road-side with flush-boxes coming to the surface every two hundred yards. This system, costing from eight to ten times that of a thoroughly built pole line, never worked satisfactorily, and soon had to be abandoned. On August 16 Queen Victoria sent a telegram of congratulation to President Buchanan through the line, and expressed a hope that it would prove 'an additional link between the nations whose friendship is founded on their common interest and reciprocal esteem.' The President responded that, 'it is a triumph more glorious, because far more useful to mankind, than was ever won by conqueror on the field of battle. With delicate relays, and more especially with quick working printing telegraphs, or automatic telegraphs, such lines are very troublesome; and, with telephones, the retardation is a very troublesome matter on under-ground lines ten miles long. 2. The second difficulty is called induction, and is noticed when two or more wires are run side by side and near together, as they necessarily are in an under-ground cable.