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.