And, in fact, Lemond's telegraph was of the most interesting character, for it was a single wire one, and we already find here an alphabet based upon the combination of a few elementary signals.
The apparatus that next succeeds is the electric telegraph that Reveroni Saint Cyr proposed in 1790, to announce lottery numbers, but as to the construction of which we have no details. In 1794 Reusser, a German, made a proposition a little different from the preceding systems, and which is contained in the Magazin für das Neueste aus der Physik und Naturgeschichte, published by Henri Voigt.
"I am at home," says Reusser, "before my electric machine, and I am dictating to some one on the other side of the street a complete letter that he is writing himself. On an ordinary table there is fixed vertically a square board in which is inserted a pane of glass. To this glass are glued strips of tinfoil cut out in such a way that the spark shall be visible. Each strip is designated by a letter of the alphabet, and from each of them starts a long wire. These wires are inclosed in glass tubes which pass underground and run to the place whither the dispatch is to be transmitted. The extremities of the wires reach a similar plate of glass, which is likewise affixed to a table and carries strips of tinfoil similar to the others. These strips are also designated, by the same letters, and are connected by a return wire with the table of him who wishes to dictate the message. If, now, he who is dictating puts the external armature of a Leyden jar in contact with the return wire, and the ball of this jar in contact with a metallic rod touching that of the tinfoil strip which corresponds with the letter which he wishes to dictate to the other, sparks will be produced upon the nearest as well as upon the remotest strips, and the distant correspondent, seeing such sparks, may immediately write down the letter marked.
Will an extended application of this system ever be made? That is not the question; it is possible. It will be very expensive; but the post hordes from Saint Petersburg to Lisbon are also very expensive, and if any one should apply the idea on a large scale, I shall claim a recompense."
Every letter, then, was signaled by one or several sparks that started forth on the breaking of the strip; but we see nothing in this document to authorize the opinion which has existed, that every tinfoil strip was a sort of magic tablet upon which the sparks traced the very form of the letter to be transmitted.
Voigt, the editor of the Magazin, adds, in continuation of Reusser's communication: "Mr. Reusser should have proposed the addition to this arrangement of a vessel filled with detonating gas which could be exploded in the first place, by means of the electric spark, in order to notify the one to whom something was to be dictated that he should direct his attention to the strips of tinfoil."
This passage gives the first indication of the use of a special call for the telegraph. The same year (1794), in a work entitled Versuch über Telegraphie und Telegraphen, Boeckmann likewise proposed the use of the pistol as a call signal, in conjunction with the use of a line composed of two wires only, and of discharges in the air or a vacuum, grouped in such a way as to form an alphabet.
Experiments like those indicated by Boeckmann, however, seem to have been made previous to 1794, or at that epoch, at least, by Cavallo, since the latter describes them in a Treatise on Electricity written in English, and a French translation of which was published in 1795. In these experiments the length of the wires reached 250 English feet. Cavallo likewise proposed to use as signals combustible or detonating materials, and to employ as a call the noise made by the discharge of a Leyden jar.
In 1796 occurred the experiments of Dr. Francisco Salva and of the Infante D. Antonio. The following is what we may read on this subject in the Journal des Sciences:
"Prince de la Paix, having learned that Dr. Francisco Salva had read before the Royal Academy of Sciences of Barcelona a memoir on the application of electricity to telegraphy, and that he had presented at the same time an electric telegraph of his own invention, desired to examine this machine in person. Satisfied as to the accuracy and celerity with which we can converse with another by means of it, he obtained for the inventor the honor of appearing before the king. Prince de la Paix, in the presence of their majesties and of several lords, caused the telegraph to converse to the satisfaction of the whole court. The telegraph conversed some days afterward at the residence of the Infante D. Antonio.
"His Highness expressed a desire to have a much completer one that should have sufficient electrical power to communicate at great distances on land and sea. The Infante therefore ordered the construction of an electric machine whose plate should be more than forty inches in diameter. With the aid of this machine His Highness intends to undertake a series of useful and curious experiments that he has proposed to Dr. D. Salva."
In 1797 or '98 (some authors say 1787), the Frenchman, Betancourt, put up a line between Aranjuez and Madrid, and telegraphed through the medium of discharges from a Leyden jar.
But the most interesting of the telegraphs based upon the use of static electricity is without doubt that of Francis Ronalds, described by the latter, in 1823, in a pamphlet entitled Descriptions of an Electrical Telegraph and of some other Electrical Apparatus, but the construction of which dates back to 1816.
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.