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.