Page:The American Cyclopædia (1879) Volume XV.djvu/638

 610 TELEGRAPH it arrives: 1. The statical attractions and re- pulsions would be impracticable except with frictional electricity. 2. The chemical effect of electricity is capable of making a visible sign and also a permanent record. 3. The magnetic effect is able to make a visible sign, as in the needle telegraph ; it can also prick out its message in an artificial alphabet, or even print it in ordinary type. 4. The physio- logical effect can furnish a signal which may be felt. 5. The luminous and the calorific effects can be used for visible signals, but they cannot write or print. Of the manifold at- tempts at electric telegraphs, the best are now known to be those which employ the chemical or the magnetic effects. As the chemical tel- egraph works silently, an electro-magnet is required even in this case to attract the at- tention of the person who is to receive the message. The electro-magnetic telegraph can address the eye or the ear, and can also write or print. Attempts have been made to prove that the electric telegraph was foreshadowed more than two centuries ago. Prof. Mannoir puts in a claim for Dr. Odier on account of a letter which he wrote in 1773. But Addison, in No. 241 of the "Spectator," written in 1711, quotes from the Prolusiones Academicm of Strada a description of essentially the same arrangement as that proposed by Dr. Odier. Moreover, Schwenter in 1636 had the same idea, but borrowed from a still earlier writer. How chimerical the scheme was in all these cases, and how unworthy of being regarded as an anticipation of the real discovery, will appear from the following brief description of the project: A magnetized needle is free to move over a graduated dial, the marks be- ing the letters of the alphabet. One of these instruments stands in one place, and another in a remote city. If the needle of one is placed upon a particular letter, the needle of the other will move to the same letter by vir- tue of the magnetic forces. Du Fay, Winckler, Lemonnier, Gray, and Desaguliers made ex- periments, which, showed that the effect of electricity could be transmitted to a distance. The discovery made by Dr. Watson in 1747, that electricity would force its way through considerable lengths of wire, and that earth and water could take the place of wire in completing the circuit, furnishes the first facts of any significance in the history of the elec- tric telegraph. He transmitted shocks across the Thames and the New river, in one instance at Shooter's Hill the circuit being composed of about 2 m. of wire and 2 m. of the earth ; and he supported his wires upon posts. Franklin made similar experiments across the Schuyl- kill river in 1748, and De Luc afterward on the lake of Geneva. Signals were commu- nicated by means of the electric shook from one apartment to another by Lesage at Ge- neva in 1774, and by Lomond in France in 1787 by the divergence of pith balls on some concerted plan; and in 1794 Reizen of Ger- many employed the electric spark for tele- graphing, making use of interrupted strips of tin foil, so arranged that the form of the letter or figure was exhibited by the sparks. He em- ployed 36 wires from one station to another, each one of them communicating with one of the letters or figures, and each one connect- ing with a return wire, thus making 72 in all. This plan is described in vol. ix. of Voigt's Magazin. Cavallo in his "Treatise on Elec- tricity " (1795) suggests the explosion of gun- powder to call attention, and then the trans- mission of signals by a succession of sparks at intervals and in numbers according to the sys- tem agreed upon. Don Francisco Salva of Madrid and Sr. Betancourt constructed similar telegraphs at Madrid in 1797 and 1798, one of them extending between Madrid and Aran- juez, about 26 m. (Voigt's Nagazin, vol. xi.) Salva communicated his plans to the royal academy of sciences at Barcelona, and accord- ing to the journals of 1797 they were highly commended by the minister of state. Salvd appears to have had a clear idea of the prac- ticability of electric communication even be- neath the sea, and in the last of his memoirs he proposed to substitute the voltaic pile for the electrical machine. Other attempts to employ frictional electricity were made by Francis Ronalds at Hammersmith, England, in 1816, on a line of 8 m. ; and in 1827 by Harrison G. Dyar at the race course on Long Island, N. Y., on a line of 2 m. The latter made use of iron wire, glass insulators, and wooden posts, and employed for signalling the chemical power of the electric current to change the color of litmus paper. Ronalds introduced the plan of employing a clock at each of the two stations, both of them running together exactly, and each bringing into view one after the other the letters of the alphabet arranged upon a disk which revolved behind a screen with an opening for one letter. Each clock was provided with two pith balls con- nected with an electrical machine at the other station ; and their divergence called the at- tention of the other operator to the letter then in view. The voltaic pile, discovered in 1800, furnished in its continuous current a more prom- ising agent for transmitting intelligence than the sudden and transient discharge of the fric- tion machine. Sommering began his experi- ments in 1809, and devised a plan of telegraph- ing which was as perfect as was practicable at that time. He used 35 wires, terminating in gold points, set up vertically on a horizontal line at the bottom of a glass reservoir of water. In the other direction these wires, brought to- gether in a tube, extended to the other station, where they again diverged, terminating in brass plates attached to a horizontal wooden bar. The plates at one end and the points at the other were marked with corresponding letters, and whenever a momentary current was sent through any two of the plates, hydrogen was evolved at one of the gold points and oxygen at