What is peculiarly interesting in Ronalds' apparatus is that it presents for the first time the use of two synchronous movements at the two stations in correspondence.
The apparatus is represented in Fig. 2. It is based upon the simultaneous working of two pith-ball electrometers, combined with the synchronous running of two clock-work movements. At the two stations there were identical clocks for whose second hand there had been substituted a cardboard disk (Fig. 3), divided into twenty sectors. Each of these latter contained one figure, one letter, and a conventional word. Before each movable disk there was a screen, A (Fig. 2), containing an aperture through which only one sector could, be seen at a time. Finally, before each screen there was a pith-ball electrometer. The two electrometers were connected together by means of a conductor (C) passing under the earth, and which at either of its extremities could be put in communication with either an electric machine or the ground. A lever handle, J, interposed into the circuit a Volta's pistol, F, that served as a call.
When one of the operators desired to send a dispatch to the other he connected the conductor with the machine, and, setting the latter in operation, discharged his correspondent's pistol as a signal. The call effected, the first operator continued to revolve the machine so that the balls of pith should diverge in the two electrometers. At the same time the two clocks were set running. When the sender saw the word "attention" pass before the slit in the screen he quickly discharged the line, the balls of the two electrometers approached each other, and, if the two clocks agreed perfectly, the correspondent necessarily saw in the aperture in his screen the same word, "attention." If not, he moved the screen in consequence, and the operation was performed over until he could send, in his turn, the word "ready." Afterward, the sender transmitted in the same way one of the three words, "letters," "figures," "dictionary," in order to indicate whether he wished to transmit letters or figures, or whether the letters received, instead of being taken in their true sense, were to be referred to a conventional vocabulary got up in advance. It was after such preliminaries that the actual transmission of the dispatch was begun. The pith balls, which were kept constantly apart, approached each other at the moment the letter to be transmitted passed before the aperture in the screen.
Ronalds, in his researches, busied himself most with the construction of lines. He put up on the grounds near his dwelling an air line 8 miles long; and, to do so, stretched fine iron wire in zigzag fashion between two frames 18 meters apart. Each of these frames carried thirty-seven hooks, to which the wire was attached through the intermedium of silk cords. He laid, besides, a subterranean line of 525 feet at a depth of 4 feet. The wire was inclosed within thick glass tubes which were placed in a trough of dry wood, of 2 inch section, coated internally and externally with pitch. This trough was, moreover, filled full of pitch and closed with a cover of wood. Ronalds preferred these subterranean conductors to air lines. A portion of one of them that was laid by him at Hammersmith figured at the Exhibition of 1881, and is shown in Fig. 4.
Nearly at the epoch at which Ronalds was experimenting in England, a certain Harrisson Gray Dyar was also occupying himself with electrostatic telegraphy in America. According to letters published only in 1872 by American journals, Dyar constructed the first telegraph in America. This line, which was put up on Long Island, was of iron wire strung on poles carrying glass insulators, and, upon it, Dyar operated with static electricity. Causing the spark to act upon a movable disk covered with litmus paper, he produced by the discoloration of the latter dots and dashes that formed an alphabet.
FIG. 2.
These experiments, it seems, were so successful that Dyar and his relatives resolved to construct a line from New York to Philadelphia; but quarrels with his copartners, lawsuits, and other causes obliged him to leave for Rhode Island, and finally for France in 1831. He did not return to America till 1858.
Dyar, then, would seem to have been the first who combined an alphabet composed of dots and dashes. On this point, priority has been claimed by Swaim in a book that appeared at Philadelphia in 1829 under the title of The Mural Diagraph, and in a communication inserted in the Comptes Rendus of the Academic des Sciences for Nov. 27, 1865.
