Toy Cannon]

noise. Seven or eight inches is about the right length for a 1-in.
bore. Screw the plug and pipe up tightly and then drill a 1/16-in.
fuse hole at D.

If desired the cannon may be mounted on a block of wood, F, by
means of a U-bolt or large staple, E.
--Contributed by Carson Birkhead, Moorhead, Miss.

** Controller for a Small Motor [42]

An easy way of making a controlling and reversing device for small
motors is as follows:

Cut a piece of wood (A) about 6 in. by 4-1/2 in., and 1/4 in.
thick, and another piece (B) 6 in. by 1 in., and 1/4 in. thick.
Drive a nail through this near the center for a pivot (C). To the
under side of one end nail a copper brush (D) to extend out about
an inch. On the upper side, at the same end, nail another brush
(E) so that it projects at both sides and is bent down to the
level of the end brush. Then on the board put

[Illustration: Reverse for Motor]

a semi-circle of brass-headed tacks as shown at F, leaving a small
space at the middle and placing five tacks on either side, so that
the end brush will come in contact with each one. Connect these
tacks on the under side of the board with coils of German-silver
wire, using about 8 in. of wire to each coil. Fix these by
soldering or bending over the ends of the tacks. Then nail two
strips of copper (G) in such position that the side brush will
remain on the one as long as the end brush remains on the tacks on
that side.

Put sides about 1-1/2 in. high around this apparatus, raising the
board a little from the bottom to allow room for the coil. A lid
may be added if desired. Connect up as shown.
--Contributed by Chas. H. Boyd, Philadelphia.

** How to Make a Simple Water Rheostat [43]

[Illustration: Wiring Plan for Water Rheostat]

The materials necessary are: One 5-point wood-base switch, 4 jars,
some sheet copper or brass for plates, about 5 ft. of
rubber-covered wire, and some No. 18 gauge wire for the wiring.

The size of the jars depends on the voltage. If you are going to
use a current of low tension, as from batteries, the jars need not
be very large, but if you intend to use the electric light current
of 110 voltage it will be necessary to use large jars or wooden
boxes made watertight, which will hold about 6 or 7 gal. Each jar
to be filled with 20 parts water to 1 part sulphuric acid. Jars
are set in a row in some convenient place out of the way.

Next cut out eight copper or brass disks, tw