sses through a pair of metal brackets (C, D), the bracket C
having a screw to hold one of the line wires, and the other bracket
having a metal switch (E) hinged thereto. This switch bar, like the
brackets, is made of brass, one-half inch wide by one-sixteenth of an
inch thick.

Below the forward end of the key (A) is a cross bar of brass (F),
screwed to the base by a screw at one end, to receive the other line
wire. Directly below the key (A) is a screw (G), so that the key will
strike it when moved downwardly. The other end of the bar (F) contacts
with the forward end of the switch bar (E) when the latter is moved
inwardly.

[Illustration: _Fig. 67._ TELEGRAPH SENDING KEY]

The forward end of the key (A) has a knob (H) for the fingers, and the
rear end has an elastic (I) attached thereto which is secured to the end
of the base, so that, normally, the rear end is held against the base
and away from the screw head (G). The head (J) of a screw projects from
the base at its rear end. Key A contacts with it.

When the key A contacts with the screw heads G, J, a click is produced,
one when the key is pressed down and the other when the key is released.

You will notice that the two plates C, F are connected up in circuit
with the battery, so that, as the switch E is thrown, so as to be out of
contact, the circuit is open, and may be closed either by the key A or
the switch E. The use of the switch will be illustrated in connection
with the sounder.

[Illustration: _Fig. 68._ TELEGRAPH SOUNDER]

When the key A is depressed, the circuit of course goes through plate C,
key A and plate F to the station signalled.

THE SOUNDER.--The sounder is the instrument which carries the
electro-magnet.

In Fig. 68 this is shown in perspective. The base is six inches long and
four inches wide, being made, preferably, of wood. Near the forward end
is mounted a pair of electro-magnets (A, A), with their terminal wires
connected up with plates B, B', to which the line wires are attached.

Midway between the magnets and the rear end of the base is a pair of
upwardly projecting brackets (C). Between these are pivoted a bar (D),
the forward end of which rests between the magnets and carries, thereon,
a cross bar (E) which is directly above the magnets, and serves as the
armature.

The rear end of the base has a screw (F) directly beneath the bar D of
such height that when the rear end of the bar D is in contact therewith
the armature