In Search of Nikola Tesla Page 32

CHAPTER THREE The higher voltage in C would be free to go around in a complete circuit but for a break in the circuit called a 'spark gap', G. If a spark occurs at G1, then some current flows through the circuit for an instant but, in the intervals between sparks, no current flows. The overall effect is a current which is in a stop-go condition. As the sparks fly faster and faster this current vibrates rapidly between an off-on situation. In effect B contains a current of high voltage and high frequency - but still not as high a voltage as Tesla requires. G₁ A 000000 00000000000 B 00000000000 000000 C G₂ F The crucial piece of the device is the third circuit, C. It may not look very different from B; again, the current could go round in a complete circuit but for the spark gap, G². The two circuits, B and C, are connected through a transformer which produces even higher voltages in C. Probably the most important feature of the third circuit, C, is its variable condenser, which has the effect of 'tuning' the circuit. This variable condenser acts in the same way as the variable condenser in a radio set is used to select a station. By changing its capacity, it becomes possible to change the natural frequency of electrical vibrations in the third circuit. The secret of a Tesla coil is to vary the condenser until its natural frequencies, of B and C, come into resonance. When this resonance occurs, it is possible to pump energy into C. This ingenious device makes it possible to take normal household 32