WIRELESS TELEGRAPHY AND TELEPHONY. A system of wireless telegraphy has been developed through three different methods, which may be classified as conduction, induction, and wave methods. By the method of conduc tion, currents are sent through the earth from one electrode to another, at the sending station. By the induction method, use is made of a property passed by alternating currents, of exciting simi lar currents in neighboring conductors with the aim of obtaining as intense a current as possible in the secondary circuit. The two methods were com bined by W. H. Preece, of England. The third method is by the use of electro magnetic waves. This was introduced and developed by William Marconi, to whom is generally ascribed the invention of wireless telegraphy. After experi ments were carried on through many years, practical use of wireless teleg raphy was first demonstrated in the rescue of the steamship "Republic", in 1909, and of the survivors of the steam ship "Titanic", in 1912. Both of these vessels were equipped with wireless teleg raphy by which notification of disasters was given. Within a short period, all trans-Atlantic steamers and naval vessels were fitted with wireless telegraph ap paratus, and wireless stations were erected in many parts of the United States, the British Isles, continental Eu rope, and other parts of the world. Serv ice between the Eiffel Tower, Paris, and the United States was put into effect in 1911, and in 1913 wireless communication was established between Sayville, L. I., and Nauen, Germany. Direct communi cation by wireless telegraphy was estab lished between the United States and Japan in 1915. During the World War practically all war vessels, including sub marines, were equipped with wireless ap paratus. Aeroplanes were likewise
equipped with wireless installations and these proved an effective means of lo cating enemy troops and batteries. Wireless telegraphy was developed to a high state of efficiency during the war. It is also used for commercial purposes and in the transmission of news and com mercial matter. The United States has established a widespread system of aerial communication. Stations are established at Arlington, Va., Panama Canal Zone, San Francisco, Pearl Harbor, Hawaii, in Samoa, and in the Philippine Islands.
Wireless Telephony. — A system of telephone communication in which the action of the transmitter brings about fluctuations in electric waves which are radiated through space by a high frequency current. These fluctuations are reproduced at the distant station in the form of the original sounds. Wire less telephony differs from wireless telegraphy in that the transmission of waves is continuous instead of inter rupted. Wireless telephony has become a practical method of communication be tween ships at sea and between moving railroad trains. The distance to which sounds can be transmitted is practi cally limitless. Communication is held between New York and San Francisco, and between Arlington, Va., and Hono lulu. The system was developed to a point of great efficiency in aeroplanes during the war. This use was especially notable in the great Meuse-Argonne cam paign of 1918, when the American Signal Corps successfully directed operations beyond the lines by the um of wireless telephony.