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

TIHE TRANSMITTING APPARATUS. 257
also another key at 7, for uniting the wire D and D. In this
figure, however, the keys themselves are omitted, in order to
render more clear the arrangement of wires under and around
them. Another figure, 2, is here introduced to illustrate the
plan of one set of wires and their two keys. In fig. 2 is represented, in a top view, the two wooden keys, A and B, and
their axes, at E and P. G is the battery, of which 9 is the
positive pole, and 10 the negative pole. The small circles,
marked 1, 2, 3, 4, 5, 6, 7, and 8, represent the mercury cups.
c and c', and also D, are the extended wires. The keys, A and
B, have each two wires, passing at right angles through the
wooden lever. The wires of the key A are marked 1 and 2,
and 5 and 6, and those of the key B are marked 3 and 4, and
7 and 8. These wires, directly over the mercury cups, are bent
down a convenient length, so as to become immersed in the
cups, when the lever is depressed, and rise out of them, when
the lever is elevated. Now, if the key A is depressed, the cup
1 is brought in connection with cup 2; and 5 is connected with
6 by the wires, supported by the lever, being immersed in the
mercury; and the key B not being depressed, there is no connection of the cup 3 with 4, or 7 with 8. At x and x, under
the lever, are springs, which keep the lever elevated, and, consequently, the wires out of the cups, when the keys are not
pressed down.
Fig. 3.
Cl CC
Fig. 3 represents a side view of the lever or key A, and its
axis at E. R is the platform supporting the standard of the
axis, the stationary wires, the battery G, and the mercury cups,
ac and 10. x is the spiral spring, for the purpose of carrying
back the lever, after the finger is taken off, and sustaining it
in its elevated position. Through the centre of the spiral passes
a rod, with a head upon it at the top of the lever, to limit its
upward motion. At its lower end, the rod is secured in the
platform R. 4 and 8 are the two wires supported by the lever
A, and are seen to project down directly over the mercury cups,
a and a, so that by depressing the key, they both enter the cups
17