FIG. 95.—Transmitting condenser (molded dielectric).
Directive Wireless Telegraphy is an interesting phase of this new art which is receiving considerable attention in the hands of investigators and has resulted in the devisement of several successful systems for confining the propagation of the electric waves to certain directions.
FIG. 96.—Braun's method for directing wireless telegraph signals.
A general diffusion of waves is often very undesirable for the reasons that the message may be received by an unfriendly neighbor or enemy and also because it is wasteful of energy. By so directing the waves that they may be sent over the earth to any desired point of the compass and only in that direction, it is possible to communicate without disturbing another station and also for a vessel at sea to secure its bearings and position by tuning its apparatus to respond to electric waves from two different known stations.
The manner in which the problem has been solved varies considerably according to the inventor. All are interesting and ingenious.
It will be remembered that electric waves possess all the characteristics and properties of light waves, etc., and may be reflected, refracted and polarized.
Ferdinand Braun has devised a system consisting of a number of metallic strips arranged to compose a parabolic surface. Another similar set of strips below the first set completes the arrangement. The two sets are connected to the terminals of a spark gap and induction coil. This apparatus acts as a huge reflector and sends out waves in one direction only, but however interesting and ingenious it may be is not entirely practical.
