oot Rule and Hammer [106]

An example of unstable equilibrium is shown in the accompanying
sketch. All that is needed is a 2-foot rule, a hammer, a piece of
string, and a table or bench. The experiment works best

[Illustration: An Experiment in Equilibrium]

with a hammer having a light handle and a very heavy head.

Tie the ends of the string together, forming a loop, and pass this
around the hammer handle and rule. Then place the apparatus on the
edge of the table, where it will remain suspended as shown.
--Contributed by Geo. P. Schmidt, Culebra, Porto Rico, W. I.

** Simple Current Reverser [107]

On a block of hardwood draw a square (Fig. 1) and drill a hole in
each corner of the square. Fill these holes with mercury and
connect them to four binding posts (Fig. 1).

On another block of wood fasten two wires, as shown in Fig. 2, so
that their ends can be placed in the holes in the first block.
Then connect up with the

[Illustration: Details of Reverser]

motor and battery as in Fig. 3. When the block is placed on with
the big arrow A pointing in the direction indicated in Fig. 3, the
current flows with the small arrows. To reverse turn through an
angle of 90 degrees (Fig. 4). -- Contributed by F. Crawford Curry,
Brockville, Ontario, Canada.

** Alarm Clock to Pull up Furnace Draft [107]

A stout cord, A, is attached to the draft B of the furnace, run
through a pulley, C, in the ceiling and has a window weight, D,
attached at the other end. A small stick is put through a loop in
the cord at about the level of the table top on which the alarm
clock F stands. The other end of stick E is placed under the key G
of the alarm clock. When the alarm rings in the early morning, the
key turns, the stick

[Illustration: Automatic Time Draft-Opener]

falls away, releasing the weight, which pulls the draft open.
--Contributed by Edward Whitney, 18 Gorham St., Madison, Wis.

** How to Transmit Phonograph Music to a Distance [107]

An interesting experiment, and one calculated to mystify anyone
not in the secret, is to transmit the music or speech from a
phonograph to another part of the house or even a greater
distance. For an outdoor summer party the music can be made to
come from a bush, or tree, or from a bed of flowers. The apparatus
is not difficult to construct.

The cut shows the arrangement. Procure a long-distance telephone
transmitter, D, including the mouthpiece, and fasten it to the