have a practical reality, and that they were pure speculations which it
is erroneous to consider as the first ideas of the electric telegraph.

We shall make a like reserve with regard to certain apparatus that
have really existed, but that have been wrongly viewed as electric
telegraphs. Such are those of Comus and of Alexandre. The first of these
is indicated in a letter from Diderot to Mlle. Voland, dated July 12,
1762. It consisted of two dials whose hands followed each other at a
distance, without the apparent aid of any external agent. The fact
that Comus published some interesting researches on electricity in the
_Journal de Physique_ has been taken as a basis for the assertion that
his apparatus was a sort of electrical discharge telegraph in which the
communication between the two dials was made by insulated wires hidden
in the walls. But, if it be reflected how difficult it would have been
at that epoch to realize an apparatus of this kind, if it be remembered
that Comus, despite his researches on electricity, was in reality only a
professor of physics to amuse, and if the fact be recalled that cabinets
of physics in those days were filled with ingenious apparatus in which
the surprising effects were produced by skillfully concealed magnets, we
shall rather be led to class among such apparatus the so-called "Comus
electric telegraph."

We find, moreover, in Guyot's _Recreations physiques et
mathematiques_--a work whose first edition dates back to the time at
which Comus was exhibiting his apparatus--a description of certain
communicating dials that seem to be no other than those of the
celebrated physicist, and which at all events enables us to understand
how they worked.

Let one imagine to himself two contiguous chambers behind which ran