The supports are made of hard rubber instead of wood, because the rubber has a greater insulating value than the wood. High-frequency currents are very hard to insulate, and wood does not usually offer sufficient insulation.
A brass rod, five inches long and having a small brass ball at one end, is mounted on the top of each of the hard-rubber supports. The ends of the secondary winding are connected to the brass rods.
Fig. 321.—End View of the Complete Tesla Coil.
The lower end of each of the hard-rubber supports is fastened to the base by means of a screw passing through the base into the support.
In order to operate the Tesla coil, the primary should be connected in series with a condenser and a spark-gap as shown in Figure 324. The condenser may consist of a number of Leyden jars or of several glass plates coated with tinfoil. It is impossible to determine the number required ahead of time, because the length of the connecting wires, the spark-gap, etc., will have considerable influence upon the amount of condenser required. The condenser is connected directly across the secondary terminals of the spark coil.
When the spark coil is connected to a battery and set into operation, a snappy, white spark should jump across the spark-gap.
If the hand is brought close to one of the secondary terminals of the Tesla coil, a small reddish-purple spark will jump out to meet the finger.
Fig. 322.—The Complete Tesla Coil.