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to one of any one of the turns forming the primary. In
this way the number of turns in the primary is changed
and the circuit is tuned in the same way that wireless appa-
ratus is tuned by changing the number of turns in the
tuning coil or helix.

The weird beauty of a Tesla coil is only evident when it
is operated in the dark. The two wires leading from the





rmrou. \



Fro 323. — Showing how a Glass-Plate Condenser is built up of
Alternate Sheets of Tinfoil and Glass.

secondary to the brass rods and the ball on the ends of the
rods will give forth a peculiar brush discharge.

If you take a piece of metal in your hand and hold it
near one of the secondary terminals, the brushing will 'in-
crease. If you hold your hand near enough, a spark will
jump on to the metal and into your body without your
feeling the slightest sensation. .

If one of the secondary terminals of the Tesla coil is
grounded by means of a wire connecting it to the primary,
the brushing at the other' terminal will increase considerably.

Make two rings out of copper wire. One of them should
be six inches in diameter and the other one four inches in

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