HISTORY. In 1795 Sala, a Spanish physicist, suggested that it might he possible to charge the earth at Majorca with positive electricity and that at Alicante with negative electricity, when the attraction of the opposite changes would establish communication between the two cities. The earliest actual experiment by which it was demonstrated that an electrical connection could be established between a transmitting and a receiving instrument with only water as a con necting medium was performed by SiMimerring of Munich on June 5, 1811; this lie (lid by the dispersion or leakage method. The next step to ward wireless telegraphy was made when Stein lieu] accidentally discovered in 1838 that by grounding the terminals of a single telegraph wire the earth would act as a conductor for the returning electrical energy. Prior to this time the Morse wire telegraph employed a complete metallic circuit, which was evidently a modifica tion of the leakage method. To Morse appears due the credit of making the first practical test of wireless telegraphy based on the principles of the dispersion of an electric current. lie having connected Island with Castle Garden, New York, a distance of a mile.
In 188n Amos E. Dolbear of Tufts College. Mass.. evolved his electrostatic method of wire less telegraphy. by which he was enabled to trans mit and receive signals'a distance of half a mile. Thomas A. Edison in 1891 took out a United States patent on what he termed an induction method. but it was based on the principles of electrostatics. Wireless telegraphy' by true in duction gore so little promise that flu at tempts were made to apply it until 1891, when John Trowbridge advocated the method and de duced the conclusions necessary to be attained for transatlantic signaling. In 189n, however, a new method was brought to light by William Marconi, and although the principles underlying it were known, its practical application had not as yet been tested. This was the electric wave method, and its history began with Michael Faraday's theory of the electromagnetic origin of light in 1845. This theory was deduced mathe
matically by James Clerk Maxwell in 1sn4, but it was not until 1888 that it received a physical demonstration, when Heinrich Hertz experi mentally proved that electric waves followed exactly the same laws as light waves. But Hertz did more; he showed how to produce these electric waves by purely physical means as well as how to detect them.
His apparatus, especially his wave detector, was crude, consisting merely of a circlet of wire severed at a given point so that an air-gap formed a miscroscopie portion of it. llis trans mitter was not unlike those in use at the pres ent time in wireless telegraphy; it consisted of an induction coil, battery, key, and oscillator. This was the real beginning of wireless teleg raphy, and from this time its development may be said to date.
What was now needed to transmit signals to greater distances was a more sensitive detector, and this was forthcoming in 1890. when Eduard Branley constructed his radio-conductor or co heror. consisting of a little glass tube contain ing some metal filings. This was a marvelously sensitive detector to the electric radiations. In 1895 Professor Popoff employed the coherer in meteorological observations. and connected one of the coherer terminals to an aerial wire and the opposite terminal to the earth; a relay, elec tric bell. and battery completed the apparatus.
Marconi in 189G produced the first wireless telegraph capable of propagating and indicating electric waves over long distances. This he did by connecting one side of the spark-gap to an aerial wire and the opposite side to the earth. By adapting the receiver of Popoff, connecting an aerial and earthed wire to the receive-, and improving the coherer he was enabled to send messages a distance of 300 feet on his arrival in England in 189(1; this distance he gradually ex tended until now it is possible to signal without cables across the _Atlantic ?Iceart.