Wireless Telegraphy and Telephony

l6 WIRELESS TELEGRAPHY sance.” In reality, it is caused by atmospheric electricity. When atmospheric electricity “jumps,” it is called ^light- ning-.” A lightning discharge sets up very powerful waves in the ether, which strike the aerial of the wireless station and produce a peculiar rumbling, scratching sound in the telephone receivers, and sometimes seriously interfere with a message. In fact, it is possible for a wireless operator to predict a thunder shower by many hours from the sounds he is able to hear in his telephone receivers. The cause of lightning is the accumulation of electric charges in the clouds. The electricity resides on the sur- face of the particles of water in the cloud. These charges grow stronger as the particles of water coalesce to form larger drops, because, as they unite, the surface increases proportionally less than the volume and, being forced to lodge on a smaller space, the electricity becomes more “concentrated,” so to speak. For this reason the combined charge on the surface of the larger drop is more intense than were the charges on the separate particles, and the “potential” is increased. As the countless multitudes of drops grow larger and larger, in the process of forming rain, the cloud soon becomes heavily charged. Through the effects of a phenomenon called “induction,” a charge of the opposite kind is produced on a neighboring cloud or on some object of the earth beneath. These charges continually strive to burst across the intervening air and neutralize each other. As soon as the potential becomes sufficient to break down this layer of air, a light- ning stroke from one to ten miles long takes place. The heated air in the path of the lightning expands with great force, but immediately other air rushes in to fill the partial vacuum, thus producing atmospheric waves, which impress the ear as the sound called thunder. Wireless stations belonging to the United States navy