hich is fired by means of a fuse.
--Contributed by Henry Peck, Big Rapids, Mich.

** Simple Electric Lock [60]

The illustration shows an automatic lock operated by electricity,
requiring a strong magnet, but no weights or strings, which
greatly simplifies the device over many others of the kind.

[Illustration: Lock Operated by a Magnet]

The weight of the long arm, L, is just a trifle greater than the
combined weights of the short arms, A and S. The fulcrum of the
lever is at C, where there is a staple. The lever swings on one
arm of the staple and the other arm is so placed that when the
lever is in an upright position, with the long arm at L', it will
not fall because of its greater weight but stays in the position
shown. The purpose of this is to leave the short arm, A, when in
position at A', within the reach of the magnet. Arm L rests on an
L-shaped hook, H; in this position the door is locked.

To unlock the door, press the button, B. The momentum acquired
from the magnet by the short arms, A and S, is sufficient to move
the long arm up to the position of L'. To lock the door, press the
button and the momentum acquired from the magnet by the short
arms, now at A' and S', is sufficient to move the long arm down
from L' to the position at L.
--Contributed by Benjamin Kubelsky, Chicago.

** Direct-Connected Reverse for Small Motors [60]

A simple reverse for small motors can be attached directly to the
motor as shown in Fig. 1. Fig. 2 shows the construction of the
reverse block: A is a strip of walnut 5/8 in. square and 3/8 in.
thick with strips of brass or copper (BB) attached as shown. Holes
(CC) are drilled for the wire connections and they must be flush
with the surface of the block. A hole for a 1/2 in. screw is bored
in the block. In Fig. 1, D is a thin strip of walnut or other
dense, hard wood fitted to the binding posts of the brush holders,
to receive the screw in the center.

Before putting the reverse block on the motor, remove all the
connections between the lower binding posts and the brush holders
and connect both ends of the field coil to the lower posts. Bend
the strips BB (Fig. 2) to the proper position to make a wiping
contact with the nuts holding the strip of wood D, Fig. 1. Put the
screw in tight

[Illustration: Direct-Connected Reverse]

enough to make the block turn a little hard. Connect as shown in
the illustration. To reverse, turn the block so the strips change
conn