CHAPTER XII

The system of Professor Braun-The Orling-Armstrong method-Further particulars of the Lodge-Muirhead system-Two American wireless methods-That of Dr. Lee de Forest, Professor Fessenden's Discoveries -His system-The future of wireless telegraphy.

HAVING given as complete an account of the Marconi system of wireless telegraphy, and of the marvelous results which it has achieved up to the present time, as is possible, it remains to refer with some detail to several rival methods that are competing for public recognition. One of the most important of these is that of Professor Ferdinand Braun, of Strasburg.

Professor Braun early came to the conclusion that the Hertzian waves penetrate the earth and water and spread out therein on every side, just as they do in the air, and that it was possible to turn them to account for the transmission of signals through earth and water. But his hopes of success in this regard were based upon the fact that, while slow currents of electricity penetrate and fill the whole diameter of a conductor, like a wire, rapidly alternating currents, or Hertzian waves, which we know, are of great velocity, only skim, as it were, along the surface,

or, at any rate, enter into the substance of the conductor to an extremely slight extent. Moreover, this penetration is the less the more quickly the alternations of current follow one after another.

Putting this law to the test in water, Professor Braun found that there are no electric waves of

FIG. 44.

any noteworthy intensity at a depth of under two meters from the point at which they enter. He accordingly devised a series of experiments to see what results he could obtain from the action of electric waves in the water. His first experiments were made in the disused moats of the old fortifications of Strasburg. One of these moats had the form shown in Fig. 44. The transmitting station was placed at one end of the moat, at the point marked a b, close to a

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quadrangular space covered with buildings, by reason of which Braun held that direct transmission by electric waves through the air was next to impossible. The receiving station-with its two wires dipping in the water—was removed farther and farther from the sending station, transmission remaining perfectly distinct so long as the experiments were confined to the main sheet of water. But immediately the receiving wires were transferred to the basin E, which was

connected with the larger body of water by a shallow channel hardly a meter in breadth, the intensity of the signals dropped off considerably, and was only restored by a corresponding strengthening of the induction coil.

In these experiments Professor Braun made use of variously contrived wave-generators, of which Fig. 45 is the simplest form. By sparking between the spheres, oscillations are excited. which are transferred to the surface of the water, whence, according to Professor Braun, they pass

in part into the water and in part are reflected. Another form of exciter is depicted in Fig. 46. This was found very effective. The condensers, C1 C2, consisted of two Leyden jars of about 2,000 centimeters capacity, the self-induction. coil of spirals of from ten to a hundred and more turns of copper wire, the diameter of the coils being from three to fifteen centimeters. The right selection of these coils was found to be very essential to favorable working.

Braun was satisfied that in these experiments the results obtained were: (1) not the effect of waves through the air, and (2) that they were not produced by induction in the sense of Preece's experiments.

Other experiments were subsequently conducted on the Rhine, and with equally favorable results. In the summer of the following year (1899) Professor Braun tested his method in the sea at Cuxhaven, when, with a Bunsen battery of eight cells and a medium-sized induction coil, and under conditions generally unfavorable, transmission to a distance of three kilometers was completely successful.

Notwithstanding this success, however, Professor Braun appears to have pursued these investigations no further, but directed his efforts in the remainder of this and a considerable portion of the ensuing year to experiments with aerial telegraphy. In these researches, as in those