X-Rays, Apparatus and Methods Page 2

Two arrangements of the induction coil are advocated. The one is known as the Tesla or "high-frequency" coil, and the other is the direct and old-fashioned use of the simple induction coil, in which the high secondary E.M.F. is delivered direct to the terminals of the tube.

The High-Frequency Coil. — Fig. 1 shows the diagram of the Tesla combination or "high-frequency" coil. It consists, as will be seen, of two induction coils, the induced secondary current of the first being used to charge a Leyden jar. The primary of the second coil is joined, in series with a spark gap, to the two coatings of the Leyden jar. When the Leyden jars are fully charged, they discharge across the air-gap, this discharge being, by well-known laws of electrical circuit flow, an oscillating one of exceedingly high frequency — millions or more oscillations per second. We thus have the primary of the second coil excited by an alternating current of exceedingly great voltage and frequency, so that its secondary produces a discharge of still greater E.M.F. and of this same high frequency. So great is this final E.M.F., that it is generally necessary to immerse the entire second coil, primary and all, in a tank of oil, since no solid insulation has yet been found capable of standing these great E.M.F.'s without breakdown.