switch; G, wire from bell to switch; H, wire from
light to switch; I, dry batteries; J, bell; X, point where a
splice is made from the light to wire leading to batteries from
brass strip under clock. Push the switch lever to the right before
retiring.

To operate this, set alarm key as shown in diagram, after two
turns have been made on the key. When alarm goes off, it turns
till it forms a connection by striking the contact post and starts
the electric bell ringing. Throw lever off from the right to
center, which stops bell ringing. To throw on light throw levers
to the left. The bell is then cut out but the light remains on
till lever is again thrown in the center,

[Illustration: Details of Alarm Construction]

In placing clock on shelf, after setting alarm, be sure that the
legs of clock are on the brass strip and that the alarm key is in
position so it will come in contact with the contact post in back
of clock. The contact post may be of 1/4-in. copper tubing, or
1/4-in. brass rod.

The advantage of this is that one can control the bell and light,
while lying in bed, by having the switch on the baseboard, near
the bed, so it can be reached without getting out of bed.
--Contributed by Geo. C. Brinkerhoff, Swissvale, Pa.

** How to Hold a Screw on a Screwdriver [337]

A screw that is taken from a place almost inaccessible with the
fingers requires considerable patience to return it with an
ordinary screwdriver unless some holding-on device is used. I have
found that by putting a piece of cardboard or thick paper with the
blade of the screwdriver in the screw head slot, the screw may be
held and turned into places that it would be impossible with the
screwdriver alone.
--Contributed by C. Chatland, Ogden, Utah.

** How to Make a Lead Cannon [338]

Any boy who has a little mechanical ability can make a very
reliable cannon for his Fourth-of-July celebration by following
the instructions given here:

[Illustration: Lead Cannon Construction]

Take a stick--a piece of curtain roller will do--7 in. long. Make
a shoulder, as at A, Fig. 1, 4 in. from one end, making it as true
and smooth as possible, as this is to be the muzzle of the cannon.
Make the spindle as in Fig. 1, 1/4 in. in diameter. Procure a good
quality of stiff paper, about 6 in. wide, and wrap it around the
shoulder of the stick, letting it extend 3/4 in. beyond the end of
the spindle, as at B, Fig. 2. Push an ordinary shingle nail
thr