To receive messages on a car, electric impulses on the telegraph wire W, sent from the vibrator of an induction coil, cause induced currents as follows: Car roof R, wire a, key K, telephone b c, car wheel and earth. In sending messages closure of key K works induction coil I C, and vibrator V, through battery B, and primary circuit d, c, f, g, and the secondary circuit a, h, i, charges the car roof and influences by induction the telegraph wire W and the telephone at the receiving station.
In 1881 William W. Smith proposed the plan of communicating between moving cars and a stationary wire by induction (U. S. Pat. No. 247,127, Sept. 13, 1881). Thomas A. Edison, L. J. Phelps, and others have further improved the means for carrying it out. In 1888 the principle was successfully employed on 200 miles of the Lehigh Valley Railroad.
FIG. 13.—WIRELESS TELEGRAPHY, INTERNATIONAL YACHT RACES, OCTOBER, 1899.
FIG. 13.—WIRELESS TELEGRAPHY, INTERNATIONAL YACHT RACES, OCTOBER, 1899.
Wireless Telegraphy, or telegraphing without any wires at all, from one point to another point through space, is the most modern and startling development in telegraphy. To the average mind this is highly suggestive of scientific imposition, so intangible and unknown are the physical forces by which it is rendered possible, and yet this is one of the late achievements of the Nineteenth Century. Many scientists have contributed data on this subject, but the principles and theories have only begun to crystallize into an art during the first part of the last decade of the Nineteenth Century. Heinrich Hertz, the German scientist, was perhaps the real pioneer in this line in his studies and observations of the nature of the electric undulations which have taken his name, and are known as “Hertzian” waves, rays, or oscillations. Tesla in the United States, Branly and Ducretet in France, Righi in Italy, the Russian savant, Popoff, and Professor Lodge, of England, have all made contributions to this art. It will aid the understanding to say, in a preliminary way, that electric undulations are generated and emitted from a plate or conductor a hundred feet or more high in the air, are thence transmitted through space to a remote point, which may be many miles away, and there influencing a similar plate high in the air give, through a special form of receiving device known as a “coherer,” a telegraphic record. The “coherer,” invented by Branly in 1891, is a glass tube containing metal filings between two circuit terminals. The electric waves cause these filings to cohere, and so vary the resistance to the passage of the current as to give a basis for transformation into a record.
In March, 1899, Signor Guglielmo Marconi, an Italian student, then residing in England, successfully communicated between South Foreland, County of Kent, and Boulogne-sur-mer, in France, a distance of thirty-two miles across the English Channel. Signor Marconi used the vertical conductors and the Hertz-oscillation principle, and his system is described in his United States patent. No. 586,193, July 13, 1897.