key. This is done by moving W to the right or
left. If the current enters at X, it will pass along C and out at Y,
when C is pressed down. By moving C up and down according to a
previously arranged set of signals, messages can be sent by means of the
electric current. (See telegraph alphabet.) This apparatus is not a good
one where the line is to be run with a "closed circuit battery," or
where it is to be used very often. It will do, however, for places where
a push-button would be too tiresome to use. The right end of C is
curved. This curve serves as a handle. D and E are wires leading from X
and Y.

APPARATUS 119.

_193. Telegraph Key._ Fig. 93. The base is 5 x 4 x 7/8 in. The key, C,
is made of two thicknesses of tin. It is made into a strip 5-1/2 x 3/4
in., then the front end is bent up for a handle, as suggested in Fig.
92, the front end being above the base so that it will not touch the
strap, D, unless it is pressed down. C is fastened to the base by a
screw, H, which also binds one end of the copper wire, C W. About 3/4
in. from H is placed X, which is a screw-eye binding-post. Under C is
the wire, W, which is used to regulate the amount of spring in C, by
moving it forward or backward. S I shows the position of a screw-eye, or
of an ordinary screw put into the base through C. The hole in C should
be made so that C can move up and down easily around the screw. This is
used to make a click when the key is allowed to spring up. The downward
click is made when C strikes D at each depression.

[Illustration: Fig. 93.]

The Strap, D, is made of tin. It is 4 x 1/2 in. before bending up the
right end a little. It is fastened to the base by the screw, F, and by
the other binding-post, Y. Its right end is raised enough to allow the
arm, E, to pass under it, but it must press down well upon E when E is
forced toward F.

The Swinging Arm or Switch, E, is also made of tin, and measures,
finished, 4-1/2 x 1/2 in. Its front end should be bent up a little for
convenience in handling it. (See Fig. 92.) E is pivoted at G by a screw,
which also binds the wire, C W. Fig. 24 shows another way to make the
pivot and connection.

194. Operation. See Fig. 99 for the details of the connections of a
home-made telegraph line. When you are using the line and telegraphing
to your friend, the switch, E, of your instrument must be open, as in
Fig. 93, and the corresponding switch on his instrument must be closed;
that is, the cir