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What Everyone Should Know About Radio History
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ship should be interrupted many times a second, a telephone receiver connected to the coil of a neighboring ship would receive a signal and s^ permit the transmission of messages. Trowbridge further pointed out that such coils would permit the determination of the relative direction of the two ships from each other, a role fdled to-day by the radio compass.
DOLBEAR, EDISON, AND STEVENSON
In 1883 Dolbear described his scheme for wireless signaling in which he used at each station an elevated wire, grounded on only one end; he was able to get communication over a distance of half a mile and some of his notes on the working of his scheme indicate that he was very close to a real solution of the problem.
In 1885 Edison and his associates devised a scheme for signaling to moving trains by induction from the telegraph wires running parallel to the railroad tracks. The currents induced in the train receiving apparatus were received with the train at high speed and the system had the advantage that the same wires could be used simultaneously for regular telegraph traffic. In Edison's apparatus the currents had to "jump" from the telegraph wires to
the train, a distance of thirty to forty feet; it was evidently to this extent a system of wireless telegraphy.
The most remarkable achievement using the principle of magnetic induction was accomplished by Stevenson in England in 1892; he was able to establish reliable communication from the mainland to an island half a mile distant, using at his two stations large horizontal coils two hundred yards in diameter. In the transmitting coil the current from a few cells
THOMAS A. EDISON
was interrupted by scratching a contact on a file and in the receiving coil a telephone receiver was used for detecting the induced currents.
WHY "wireless" changed TO "rADIO"
We have now come to the point in the development of wireless communication where the really important work begins; it is worth while to review what had been done m the rather more than half century which had elapsed since Steinheil had used the earth for one of the conductors of his telegraph system
and had then put forth the proposition to do away completely with any wire connecting the two stations communicating with each other. A host of experimenters had worked on Steinheil's idea of using the earth or water as the only connection between the two stations, with some success, the most promising being the work of Bell ; the feasible distance of communication by this scheme, however, seemed to be sharply limited to a few miles at most. Electrostatic as well as electromagnetic induction had both had their adherents, and considerable success had rewarded their efforts as evidenced by Edison's telegraphy with moving trains and Stevenson's transmission from mainland to island. The promise of much greater distance was rather slight with all of these schemes, however, and the time was ripe for the introduction of some new and radical step in the problem.
This new step was rapidly forthcoming; the energy radiated by very high frequency alternating currents and some simple scheme for detecting the high frequency currents, were the new concepts which were to give the development the wonderful progress which it