hree-Way Cock for Small Model-Work [50]

[Illustration: Three-way Valve]

In making models of machines it is often necessary to contrive
some method for a 3- or 4-way valve or cock. To make one, secure a
pet cock and drill and tap hole through, as shown in the cut. If
for 3-way, drill in only to the opening already through, but if
for a 4-way, drill through the entire case and valve. Be sure to
have valve B turned so as to drill at right angles to the opening
through it. After drilling, remove the valve, take off the burr
with a piece of emery paper and replace ready for work.

** Easy Experiments with Electric-Light Circuit [50]

An electric-light circuit will be found much less expensive than
batteries for performing electrical experiments. The sketch shows
how a small arc light and motor may be connected to the light
socket, A. The light is removed and a plug with wire connections
is put in its place. One wire runs to the switch, B, and the other
connects with the water rheostat, which is used for reducing the
current.

[Illustration: Arc-Light Motor and Water Rheostat]

A tin can, C is filled nearly to the top with salt water, and a
metal rod, D, is passed through a piece of wood fastened at the
top of the can. When the metal rod is lowered the current
increases, and as it is withdrawn the current grows weaker. In
this way the desired amount of current can be obtained.

By connecting the motor, E, and the arc light, F, as shown, either
one may be operated by turning switch B to the corresponding
point. The arc light is easily made by fastening two electric
light carbons in a wooden frame like that shown. To start the
light, turn the current on strong and bring the points of the
carbons together; then separate slightly by twisting the upper
carbon and at the same time drawing it through the hole.

** How to Make an Interrupter [51]

The Wenult interrupter is an instrument much used on large coils
and is far more efficient than the usual

[Illustration: Details of Interrupter]

form of vibrators. It can also be used with success on small coils
as well as large. Although it is a costly instrument to purchase,
it can be made with practically no expense and the construction is
very simple.

First procure a wide-mouthed bottle about 4 in. high, provided
with a rubber stopper. This stopper should be pierced, making two
holes about 1/4 in. in diameter. From a sheet of lead 1/16 in. in
thickness

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