Wireless Telegraphy and Telephony

WIRELESS TELEGRAPHY 135 charged with electricity and called “ions.” These ions pass through the grid and discharge against the plate. When the aerial is connected to the “grid,” and the plate to the ground, the stream of ions carries that part of the alter- nating current in the aerial which flows in the same direc- Fig. 149.—Showing the brush discharge from a Marconi transatlantic aerial at night. tion, across, but does not allow the current tending to pass in the opposite direction. In reality it is a valve, or “recti- fier,” opening one way and closing the other; thus changing the current into an intermittent, direct current, capable of manifesting itself in a telephone receiver. The Audion is a very sensitive device, and is much em- ployed for wireless telephone purposes. With such a system it has been found possible to trans- mit speech and music to a distance of two hundred miles. In fact, even greater distances have been covered, and there