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But as soon as the electric current ceases, the magnetic power of the core is lost. Hence it is called an electro-magnet, or a temporary magnet, to distinguish it from a permanent magnet. While the discovery of the electro-magnet was very important in the respect that it afforded great magnetic power by the use of a limited or economic galvanic force, or, in other words, by the use of smaller and fewer Voltaic batteries, it was not until Faraday began his splendid series of electrical discoveries, in , that a new and exhaustless wellspring of electricity was found to lay at the door of science.
He began his experiments with what became known as an induction coil, which, though then crude in his hands, is the same in principle to-day. It consists 26 of an iron core wrapped with two coils of insulated wire. One coil is of very lengthy, thin wire, and is called the secondary coil.
The other is of short, thick wire, and is called the primary. When a magnetic current is passed through the primary coil, with frequent makes and breaks, it induces an alternating current of very high tension in the secondary coil, thus powerfully increasing its effects. So magnets were found to have a similar effect upon one another. The secret of these phenomena was found to lie in the fact that a magnet, or a conductor carrying a current, was the centre of a field of force of very considerable extent.
Such a field of force can be familiarly shown by placing a piece of glass or white paper sprinkled with fine iron filings upon the poles of a magnet. So also the extent of the field of force surrounding a conductor carrying a current may be familiarly shown. In these instances the filings brought within the fields of force are magnetized. So would any other conducting substance be, and would become capable of carrying away as an independent current that which had been induced in it. Here we have the essential principle of the modern dynamo-electric machine, commonly called simply dynamo.
Faraday actually constructed a dynamo, which answered very well for his experiments, but failed in commercial results because the only source of energy he could draw upon in his time was that supplied by the rather costly voltaic cells. From the date of the discovery that electricity could be conducted to a distance, dreams were indulged that it could be made a means of communicating 27 intelligence.
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In the eighteenth century, many attempts were made to carry intelligent signals over electric wires. Some of these were quite ingenious, but in the end failures, because the old-fashioned frictional electricity was the only kind then known and employed. Even after the discovery of the voltaic cell or battery, which afforded an ample supply of chemical electricity to operate a telegraphic apparatus, the time was not ripe for successful telegraphy, for up till no battery had been produced that was sufficiently constant in its operation to supply the kind of current required.
For feasible telegraphy, two important steps were yet necessary. One was the discovery of the electro-magnet, — But even before these two indispensable requisites had been supplied by human genius, much had been done to develop the mechanical methods of conveying intelligence.https://kinun-houju.com/wp-content/ryfafapi/345.php
In , Ronalds, of England, constructed a telegraph by means of which he operated a system of pith-ball signals which could be understood. In , Dyar, of New York, perfected a telegraph by means of which he made tracings and spaces upon a piece of moving litmus paper, which tracings and spaces could be intelligently interpreted through a prearranged code. A little later, , Baron Schilling constructed a telegraph which imparted motion to a set of needles at either end. From this time up to , which last year was a memorable one in the history of telegraphy, the genius of such distinguished men as Morse in America, Wheatstone and Cooke in England, and Steinhill in Munich, was brought to bear on the further evolution of the telegraph.
While all these names have been associated with the invention of the first practical telegraph, it is impossible, with justice, to rob that of Morse of the distinguished honor. Morse conceived his invention on board the ship Surry, while on a voyage from Havre to New York, in October, It consisted, as conceived, of a single circuit of conductors fed by some generator of electricity. He devised a system of signs, which was afterwards improved into the Morse alphabet, consisting of dots or points, and spaces, to represent numerals. These were impressed upon a strip of ribbon or paper by a lever which held at one end a pen or pencil.
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The paper or ribbon was made to move along under the pencil or pen at a regular rate by means of clockwork. In accordance with these conceptions, Morse completed his instrument and publicly exhibited it in In this form it was entirely original in the important respects that the ribbon or paper was made to move by clockwork, while a pen or pencil gave the impressions, thus preserving a permanent record of the message conveyed.
In that year, amid the jeers of congressmen and the adverse predictions of the press, Morse erected the first American telegraph line in America, between Baltimore and Washington, a distance of 40 miles, and, to the confusion of all detractors, sent the first message over it on May 27 of that year. From that date the fame of Morse was established at home, and soon became world-wide. His system of telegraphy, with slight modifications, became that of all civilized countries. As was to be expected in a century so full of enterprise as the nineteenth, a science so attractive, so useful to civilization, so commercially valuable, so full of possibilities, as telegraphy, could not remain at rest.
Everywhere it stimulated to improvement and new invention and discovery; and as the century progressed, it witnessed in steady succession the wonders of what became known as duplex telegraphy, that is, the sending of different messages over the same wire at the same time. Again, the century witnessed the invention of quadruplex telegraphy, that is, the sending of four separate messages over the same wire, two in one direction and two in another.
In the cities, supporting poles proved to be unsightly and dangerous, and they were succeeded by underground conduits carrying insulated wires. In , we read of what may be reckoned the first successful experiment in telegraphing under water by means of an insulated wire, or cable, as a conductor. The experiment was tried at Calcutta, and under the river Hugli. In , Morse experimented at New York with an under-water cable, and showed that a successful submarine telegraphy was practical.
In , a cable, insulated with gutta-percha, was laid under water between New York and Jersey City, and successfully operated. In , a submarine cable was laid and successfully operated under the English Channel. An enterprising American, Cyrus W.
Field, of New York, now took up the subject of submarine telegraphy, and suggested a cable under the ocean between Ireland and Newfoundland. One was laid in , but it unfortunately parted at a distance of three hundred miles from land. A second was laid under Mr. These disasters, though furnishing much valuable experience, checked the enterprise of submarine telegraphy for a number of years.
Not until , when a deep-sea cable was successfully laid and operated between Malta and Alexandria, and in , when one was laid across the Persian Gulf, did enterprise gain sufficient courage to dare another attempt to cable the Atlantic. In , that attempt was made. Again the cable broke, but this did not dissuade from another and successful attempt in What the overland telegraph has done toward bringing local states and communities into contact, the submarine cable has done for the remote nations.
In form, an ocean cable differs much from the simple wire which constitutes the conductor of an overland or even underground telegraph. It is made in many ways, but mostly with a central core of numerous copper wires, which are more flexible than a single wire. These are thickly covered with 30 an insulating material, such as gutta-percha, after first being heavily wrapped in tarred canvas or like material.
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The central cores may be one, two, three, or even more in number. Where a cable is likely to be subjected to the abrasion of ship-bottoms, rocks, or anchors, it has an outer covering or guard composed of closely united steel wires. In submarine telegraphy, the instruments used in sending and receiving the message are very much more ingenious, delicate, and costly than in overland telegraphy.
Whereas at the beginning of the nineteenth century electric telegraphy was an unknown science, and even up to the middle of the century was of limited use and doubtful commercial value, nevertheless the end of the century witnesses in its growth and application one of its most stupendous marvels. From the few miles of overland wires in , the total mileage of the century has expanded to approximately 5,,, and the submarine to , A single company the Western Union in the United States operates , miles of wire, conveying 60,, messages per year, while throughout the world more than ,, messages per year serve the purposes of enlightened intercourse.
The capital employed reaches many hundreds of millions of dollars. The close of the nineteenth century opened possibilities in telegraphy that may be classed as startling in comparison with its previous attainments. It would seem that the intervention of the familiar conducting wire is not absolutely necessary to the transmission of intelligence. This system has been put to practical use on at least one railway, and pronounced feasible. But a greater marvel than this springs from the discovery of Hertz, about , that every electrical discharge is the centre of oscillations radiating indefinitely through space.
The phenomenon is likened to the dropping of a stone in a placid lake. Concentric undulations of the water are set up,—little waves,—which gradually enlarge in diameter, and affect in greater or less degree the entire surface. In , Professor Branley found that the electric vibrations in ether could be detected by means of fine metallic filings. No matter how good a conductor of electricity the metal in mass might be, when reduced to fine filings or powder it offered powerful resistance to a passing current; in other words, became a very poor conductor.
An electric discharge or spark near the filings greatly decreased their resistance.
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If the filings were jarred, their original resistance was restored. Branley placed his filings in a tube, into either end of which wires were passed. These were connected with a galvanometer. Ordinarily, the resistance of the filings was such as to prevent a current passing through them, and the galvanometer remained unaffected. But when an electric spark was emitted near the tube, the resistance was so 31 much decreased that the current passed readily through the filings, and was detected by the galvanometer.
This is simply equivalent to saying that the discharge of the electric spark made the filings to cohere and become a better conductor than when lying loosely in the tube. Here, then, was opportunity for an instrument which had but to regulate the number of sparks and indicate the presence of the electric waves in order to produce dots and dashes similar to those used in the common telegraph. Such an instrument was brought nearest to perfection by Signor Marconi, a young Italian, in With it he succeeded in sending electric waves through ether or space, and without the use of wires, a distance of four miles, upon Salisbury Plain, England.
Later, he transmitted messages by means of space wireless telegraphy across Bristol Channel, a distance of 8. Whether space telegraphy will eventually supersede that by wires is one of the problems that time only can solve. But such are the possibilities of electrical science that we may well be prepared for more wonderful revelations than any yet made. Telegraph Gr. Telephone Gr.