cally undoes whatever is done by the other switches. In the
accompanying diagram only two reversing switches are shown and the
lights can be independently controlled from four distinct
positions. Any number of reversing switches can be placed between
the two-way switches A and D to increase the number of places from
which the lights could be turned on and off.
--Contributed by J. S. Dow, Mayfield, London.

** How to Make an Electric Pendant Switch [310]

It is often desired to use a pendant switch for controlling
clusters of incandescent lamps. When such a switch is not at hand,
a very good substitute can be made by screwing a common fuse plug
into a key socket and connecting the socket in series with the
lamps to be controlled. In this way you get a safe, reliable,
fused switch.
--Contributed by C. C. Heyder, Hansford, W. Va.

** Measure [310]

Never guess the length of a piece of work--measure it.

** Home-Made Water Motor [311]

The small water motor shown in the illustration is constructed in
the same manner as a German toy steam turbine. The wheel, which is
made of aluminum 1/16 in. thick and 7 in. in diameter, has 24
blades attached to it.

The lugs or extensions carrying the rim must be made from the
metal of the wheel, therefore a circle 8 in. in diameter must be
first described on the aluminum plate, then another circle 7 in.
in diameter within the first and then a circle for the base of the
blades, 3-1/2 in. in diameter. Twenty-four radial lines at equal
distances apart are drawn between the two smaller circles and a
1/4-in. hole drilled at the intersecting points of the radial
lines and the innermost circle.

Centrally between each pair of radial lines and between the two
outer circles, 1/2 by 3/8-in. lugs are marked out and the metal
cut away as shown in Fig. 1. A 1/8-in. hole is then drilled in the
center of each lug. Each division is separated by cutting down
each radial line to the 1/4-in. hole with a hacksaw. Each arm is
then given a quarter turn, as shown by the dotted lines in Fig. 2,
and the lug bent over at right angles to receive the rim. The rim
is made of the same material as the disk and contains twenty-four
1/8 in. holes corresponding to those in the lugs to receive brass
bolts 1/4-in. long.

The disks PP were taken from the ends of a discarded typewriter
platen, but if these cannot be readily obtained, they can be
turned from metal or a heavy flat disk used instead.