117. SALVIONI’S EXPERIMENT. TRANSPOSITION OF PHOSPHORESCENT SPOT. _Elect. Rev._, Lon., Apr. 24, ’96, p. 550; _Med. Sur. Acad._, of Perugia, Italy, Feb. 22, ’96. Personal interview with Prof. Salvioni in _Elect. Rev._, N.Y., Apr. 8, ’96, p. 181.—In order to change the location of the phosphorescent spot when desired, without a magnet, and at the same time to concentrate or intensify the source of X-rays, he placed near the same, on the outside of the tube, the hand or a metal mass connected to earth. The spot immediately jumped to the other side of the tube, § 49, near centre, and to all appearances was smaller and brighter. Elster and Geitel had performed similar experiments at an earlier date. (See _Wied. Ann._, LVI., 12, p. 733, also _Elect. Eng._, about April, ’96.) They carried on the most minute investigations as to the deflection of the cathode rays by an outside conductor. Tesla had also noticed a similar deviation. See Martin’s _Tesla’s Researches_. He used alternating currents as described in his system in § 51. Elster and Geitel used the Tuma Alternating system. (See _Wied. Ann._, Ber. 102, part 2A, p. 1352, ’94.) The source from which Salvioni’s description was taken had no sketch, therefore the diagram made by Elster and Geitel is reproduced. See Fig. 1. The cathode was aluminum and was connected to one terminal of the transformer. The anode was connected to earth, and also was the other terminal. Upon bringing the hand or other conductor connected to earth to the phosphorescent spot, the cathode rays deviated and the spot jumped over to the other side. § 50. The anode was a ring surrounding the leading-in wires of the cathode, and the two leading-in wires were surrounded by glass. It may be asked why the cathode rays bent downward in the first place? Elster and Geitel found that they were thrown thus in view of the nearness of some neighboring object connected to earth. To overcome the action of surrounding objects, the tube was surrounded by a ring as shown in Fig. 2. However, the rays were still sensitive to objects well connected to earth, and when brought quite close to the tube. [Illustration: Figs. 1 and 2. ]