Wireless Telegraphy and Telephony

WIRELESS TELEGRAPHY 121 tube as sound waves, would strike the ear-drum and repro- duce the speech. Both of these methods were later very much improved by the employment of Koenig’s manometric flame in place of the silvered mirror as a transmitter. As explained in the last chapter, speech delivered into the mouthpiece causes the gas to become compressed or rarefied in direct accordance with the sound waves, and the flame rises and falls with a rapidity too great to be detected by the naked Fig. 137.—The Electric arc. eye. These rapid alterations in the intensity of the illumi- nation of the flame act on the selenium cell, and reproduce the original voice perfectly in the telephone receiver. It is obvious, however, that such methods as these are only capable of transmitting speech over very limited dis- tances, and if greater ranges are to be traversed much more powerful transmitters must be employed for the purpose. Ernest Ruhmer, after long and laborious researches, finally succeeded in transmitting speech many miles by taking advantage of the speaking arc, discovered by Simon, who observed that an arc lamp gave out a loud rattling noise if its current supply was interfered with. An electric arc consists of two carbon rods, connected to a generator.