bell from any ordinary electric bell. They are used in places where
the loud sound of a bell would be objectionable. As the buzzer is easier
to make than a bell, we shall discuss it first.

214. The arrangement of the parts, (Fig. 100), is very much like that of
the sounder of App. 121, Fig. 95. The armature is, in this case, a
vibrating one and acts on the same principle as the automatic
interrupter on App. 100, which you should study. (See Sec. 148.) The
general dimensions may be taken from App. 121. The base, B, in this case
is about 1 in. wide. D also is made 1 in. wide. H is 1 x 1 x 1/2 in.,
and is nailed to A. Through its center is a hole for the regulating
screw-eye, I. The end of I presses against F. The exact position of H
will have to be determined after the magnets are in place. The armature,
L, should be about 1/8 or 3/16 in. above the poles. They are not allowed
to strike the poles, as a screw, E, regulates that. (See Sec. 203). Y and
Z are two binding-posts, like App. 46. To these are connected the battery
wires. The strip of tin or copper, which forms Y, is cut like a letter T
there being three holes in it, one near the end of each arm. The
screw-eye, 2, and the screw, 3, are put through the horizontal part of
the T, and the regulating-screw, I, passes through the hole in the
vertical part which springs up against I, thus forming an electrical
connection between Y and I. The magnets are made and fastened as in App.
89.

215. Connections. The inside ends of the magnet coils, (Sec. 123), are
fastened between a screw-head and a copper bur, S. One outside end goes
to Z, and the other under the screw, G, which holds F to D.

[Illustration: Fig. 100.]

216. Adjustment. The part, F, and the screw, E, must be just high enough
to keep L from striking the poles of M. If F is too weak, it will bend
down to M. If F is too strong, it will take too much battery power to
run it. In case there is not strength enough in F to quickly raise L
when the current ceases to pass, arrange a screw-eye and rubber band as
shown in Fig. 96. I should be slowly turned one way or the other, until
it touches F just right to allow L to vibrate back and forth rapidly.

217. Operation. We shall suppose that you have all parts adjusted and
the battery wires joined to Y and Z. If the current enters at Z, it will
fly around through the coils, through G, F, up I, through the T-shaped
tin and out at Y. The current was in L, but it could not