FIG. 13.—Lightning discharge near Montclair, N. J.
"Static," that "bugbear" of the wireless operator, is very much more in evidence in the eastern parts of the United States and in South America than it is on the western coast of the country. If any one should ask a wireless operator what "static" is, he would probably reply, "a nuisance." In reality, it is caused by atmospheric electricity. When atmospheric electricity "jumps," it is called "lightning." 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 surface 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 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 lightning 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 and located on land are usually housed in a small building in the immediate neighborhood of the tall wooden mast which supports the aerial. Commercial stations are usually situated on the top floor of a high office building, or a hotel, and the aerials supported by a steel lattice-work tower. Amateurs place a small pole on the roof of the house, or in a tree, and locate their station in any convenient room near the top of the house.
FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.
FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.