The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

FRENCH ELECTRIC TELEGRAPH —THE ALPHABET. 333
a single wire, whether use is made of a special apparatus having a single indicator, or whether an apparatus is employed of
two indicators of which only one operates. This must necessarily take place when the lines have but a single wire, or when
the different wires of a line are separated in order to correspond
with several stations. In this case, the same alphabet is used
as on the instruments constructed for two wires; but the signals are divided into two parts, and are made by a single indicator. First, form the angle of the left, and then make the
angle of the right. This change, which at first seems to render the manipulation complicated, is attended with no difficulty in practice, and a few days are sufficient to accustom
the operator to its use.
The transmission by a single wire is slower than by two
wires; but the signals thus passed are not reduced to one
half. From 80 to 90 letters per minute, instead of 130, can
be sent with facility. The rapidity of transmission is claimed
to be greater than that obtained by a dial-plate apparatus, although it requires two stoppages for each letter. The reason
is explained thus: for two turns of the crank, that is to say,
for eight emissions of the current, are produced 64 combinations-while only 26 are obtained with the dial-plate apparatus, in the French instrument, and the current passes 130
times.
When two lines, each of one wire, terminate in the same station, and the operator is required to transmit in the two directions, these two wires are generally placed at the two sides of
the same apparatus, thus occupying a middle or betwixt position. Attempts have been made to use repeaters in connection
with the French system, but all the efforts have proved unsuccessful.
For ordinary purposes, however, it will be sufficient to insulate the two screws x and y, fig. 2, by means of strips of ivory,
and to make them, as well as the pallet, communicate with the
exterior binding screws, which will establish the following communication:
1st. The screw x, with another similar receiver. 2d. The
pallet with one of the lines which terminate at the post; and
3d. The screw y with the battery.