TELEGRAPH, ELECTRIC. The attempts to render one or other of tho phenomena of electricity subservient to the purposes of tele graphy, have been numerous. From the earliest date which we can assign to the existence of an electric telegraph, its essential parts have been the same. These are, 1st, the source of electrical power; 2nd, the conducting material by which this power is enabled to travel to the required locality ; and 3rd, the apparatus by which at the distant end of the line, the existence of this power, its amount, or the direc tion of its action, is made known to the observer. In the earlier stages of the invention, the investigations of its promoters were confined to the last of these three essentials; and so long as the illustration of the Idea was confined to the lecture.table, this part claimed pre-eminence. But, with the proposed application of the principle to purposes of general utility, there arose the necessity for an equal degree of atten tion to the two former requisites.
The experiments of Dr. Watson in England, in 1747, and of Franklin, in 174S, on the banks of the Schuylkill river, may have suggested the conveyance of information by means of electricity. The earliest authenticated instance of any attempt to reduce this idea to practice, appears to have been that of M. Lesago at Geneva, in 1774, and of Lomond in France, in 1787. They employed as an indicator a pair of pith balls, suspended from one end of en insulated wire, at the other end of which was the operator, provided with an electrical machine. On charging the wire with electricity, the pith balls would exercise mutual repul sion, and diverge from one another; but on removing the electrical charge from the wire by the contact of some conductor, the balls would collapse. It is evident that certain numbers of successive divergences might be made to denote particular preconcerted signals. Subsequeutiv to this, the phenomenon of the spark, as seen on the passage of electricity through an uninterrupted conductor, was used for the transmission of signals. Were the various letters of the alpha bet formed in this manner, upon a table, and connected each one with a distinct and insulated wire, any particular letter might be rendered visible in a darkened room, by passing an electrical charge through the appropriate wire. This iu fact constituted the telegraph of Ileus.ser, or Reiser, invented in 1704. Betancourt and Dr. Salve in Spain, iu 1798, appear to have made experiments on the transmission of the charge through wires of great length.
A somewhat similar form of apparatus, involving the same principle, was constructed by arranging the several wires in succession, with a single break in each. The various wires bore the names of the dif ferent letters or figures, and any required signal was indicated by passing the charge through the proper wire, when the spark visible at the interruption of the circuit would denote the letter to the observer at the farther end.
This was the point to which the invention had advanced, at the commencement of the present century. The discovery by Volta, iu 1800, of the pile which bears his name, forms the commencement of a new era in electric telegraphs, although there was no immediate application of the phenomena of the galvanic current to the purpose. Indeed S3veral important discoveries had to be made before an electric telegraph of any value was possible.
In 1807, Summering at Munich proposed to coustruct an electric telegraph on the principle of the decomposition of water by the Voltaic current, as discovered in 1800 by Nicholson and Carlisle. The form of his apparatus was the following :—In a glass trough containing water, thirty-five gold pegs or pins were arranged vertically, this number of pegs corresponding to the letters of the alphabet, together with the nine digits. Each of these pins was connected with a wire, which extended to the place whence the signal was to be transmitted. At this point they terminated in brass strips, arranged in a frame side by side, but, like the wires and pins, insulated from each other. Each brass strip bore the name of the letter or figure which belonged to the pin to which it was connected. The operator, when wishing to send any communication, connected the two poles of the battery with the brass strips bearing the names of the two first letters required. Decomposition of the water in the trough at the distant end was instantly indicated by the evolution of bubbles of gas from the two gold pins, which thus became the two electrodes or poles of the battety. The letters forming any communication were to be in this manner denoted in pairs, the inventor ingeniously availing himself of the different quantities of the two gases evolved to point out the relative position of the letters in each pair, the hydrogen being employed to indicate the first letter. Schweigger proposed to add to this system a plan for calling the atteution of the correspondent at, the distant station by the discharge, by the current, of a pistol charged with the mixed gases.