Wireless Telegraphy and Telephony

- - - . ■ ■ . - _______________________________________________________________________________________ 78 WIRELESS TELEGRAPHY wave lengths and when properly accomplished renders the apparatus highly selective. 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 devise - ment of several successful systems for confining the propa ■ gation of the electric waves to certain directions. Fig. q6.—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 waste- ful 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 appa- ratus 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.