Adjusting the spark-gap by changing its length and also altering the number of Leyden jars of condenser plates will probably increase the length of the high-frequency spark. It may be possible also to lengthen the spark by disconnecting one of the wires from the primary binding-posts on the Tesla coil and connecting the wire directly 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 apparatus is tuned by changing the number of turns in the tuning coil or helix.
Fig 323.—Showing how a Glass-Plate Condenser is built up of Alternate Sheets of Tinfoil and Glass.
The weird beauty of a Tesla coil is only evident when it is operated in the dark. The two wires leading from the 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 increase. 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 diameter. Place the small ring inside the large one and connect them to the secondary terminals. The two circles should be arranged so as to be concentric, that is, so that they have a common center.
The space between the two coils will be filled with a pretty brush discharge when the coil is in operation.
Fig. 324.—A Diagram showing the Proper Method of Connecting a Tesla Coil.