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