Nikola Tesla Books
OSCILLATION TRANSFORMERS 150 Q Fig. 6. Proportions for cone-shaped secondaries of any size of wire and to form a base or support for whatever insulating substance is applied to the wire subsequently. Secondary Insulation.-One fact stands out prominently after the worker has built and experimented with a few coils. No solid insulation of any kind is of the slightest avail when working with high frequencies and very high potentials; glass, hard rubber, mica, empire cloth, and even paraffin wax seem actually to help the current to pass. The terminals of a coil may be separated beyond sparking distance in air and when a piece of heavy plate glass is interposed, the discharge immediately starts to wind its way over the surface of the glass, finally piercing the plate as if it were of cardboard. Therefore, let the uninitiated worker bear this fact in mind: That to attempt the insulation of the Tesla primary from the secondary by means of any of the old reliables in the case of the ordinary induction coil, is the height of folly in the case of the high frequency coil. Liquid oil, freed from all moisture, is the very best insulator for these high frequency currents. It is heavy and sloppy to handle, however, and its use precludes the possibility of obtaining the beautiful brush effects from the secondary in the air. Next to oil comes a mixture of beeswax and rosin in equal parts. This seems 51
