55. PHOSPHORESCENCE OF OBJECTS WITHIN THE VACUUM TUBE.—The construction in Fig. 7, p. 17, shows how a diamond was caused to phosphoresce within a Crookes’ tube, being supported in a convenient manner in the centre of one of the tubes, while electrodes were located near the ends and were formed of disks facing the diamond. Upon connecting the disks to the respective poles of the secondary conductor, and by performing the experiment in a rather dark room, the diamond became brilliantly phosphorescent, radiating light in all directions. He experimented with many substances in this way, but found that the diamond was the best—almost equal to one candle power. In order to exhibit the phosphorescence of glass in a striking manner, he charged three small tubes simultaneously. One was made of uranium glass which radiated a green light. Another was an English glass which appeared blue, and the remaining one was German glass which phosphoresced a bright green. Notice difference with respect to light which does not perceptibly cause phosphorescence of glass. The uranium glass was the most luminous. Luminous paint, as prepared by Becquerel, and later by Balmain, which has the property of storing up light and afterwards radiating it in a dark room for several hours, became more phosphorescent in the Crookes tube than when subject to day-light. Phosphorescence of the mineral phenakite, the chemical name of which is glucinic aluminate, was blue, the emerald, crimson, and spodumene, which is a double silicate, were yellow. The ruby phosphoresced red, whatever its tint by day-light. In one tube he had rubies of all the usual tints by day-light, but they were all of one shade of red by the action of the disruptive discharge in the tube. 56. DARKNESS AND LUMINOSITY IN ARMS OF V TUBE. See Fig. 8, p. 17. It will be noticed that in Fig. 6, p. 17, the tube was straight. Crookes desired to see what effect would take place in a bent tube. He therefore employed a V shaped tube, having electrodes in the ends—one in each arm. Upon causing the electrical discharge to take place through the tube, one arm was luminous and the other was dark. Whatever the E. M. F. was, the appearances remained the same. No luminosity would bend from one arm of the V shaped tube to the other. The cathode arm was always luminous and the anode dark. With a less degree of vacuum, both arms were luminous, according to early experimenters who thus brilliantly lighted tubes of the most fantastic shapes.