51. TESLA’S EXPERIMENT. INCANDESCENT ELECTRODE BY HIGH POTENTIAL AND ENORMOUS FREQUENCY. SYSTEM REFERRED TO BY ROENTGEN FOR GENERATING POWERFUL X-RAYS. _U. S. Letters Pat._, No. 454, 622, June 23, ’91. _Martin’s Researches of Tesla_; _Trans. Amer. Inst. Elec. Engineers_, May 20, ’91; _Elec. Review_, N.Y., June 24, ’93, p. 226; _Lect. Franklin Inst._, Feb. 24, ’93, and _Nat. Elec. Light Asso._, Mar. 1, ’93; also _Lect. in Europe_. Later he again experimented in this direction, see _Elec. Review_, N.Y., May 20, ’96, p. 263.—By the U. S. Patent Office he was granted, among other claims, the following: “The improvement in the art of electric lighting herein described, which consists in generating and producing for the operation of lighting devices, currents of enormous frequency and excessively high potential, substantially as herein described.” A simple combination of circuits together with great skill in the construction of apparatus involving high powers of insulation, resulted in the production, within a vacuum, of an electrode radiating intensely white light. The circuit may be easily traced in the diagram Fig. 17 p. 17. Briefly described, there may be noticed an alternating current generator of comparatively low E. M. F. The current from this generates a secondary current by means of an induction coil. This secondary current generates a tertiary current by a second induction coil. An air-gap for automatic and intermittent disruptive discharges, § 49 near end, is in the circuit of the secondary coil of the first named induction coil, which is directly charged by the alternating current generator. The gap may be noticed between the two balls. In shunt to the air-gap is a condenser (see Fizeau, chapter I.) represented by several parallel lines. The lamp consists merely of an evacuated bulb having an electrode of carbon or other refractory material, which is connected to one pole of the last secondary coil while the other pole may be outside, and may consist, for example, of the walls of a room, which in such a case should be of some electric conducting material. The higher the vacuum the more intense the light; he found no limit to this rule. Fig. 16_a_ p. 17 illustrates his ideal method of lighting a room. He found that with two plates at a distance apart as indicated and connected to the poles of the coil, and with electrodeless vacuum bulbs, the latter became bright in space—no mechanical or electrical connection other than air and the assumed ether.