[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increases, and as it is withdrawn the current grows weaker.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.
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