66. PHOSPHORESCENCE BY CATHODE RAYS.—Substances which generally phosphoresced by light and cathode rays in the generating bulb, § 55, also phosphoresced under the influence of the rays in open air, excepting eosin, gelatin, both phosphorescent in light, were not so in cathode rays; so also with solutions of fluorescein, magdala red, sulphate of quinine and chlorophyll. Phosphorescence was less if the rays first passed through a tube of glass or tinfoil lengthwise. The phosphorescent light of the phosphides of the alkaline group, uranium glass, calcspar and some other substances, was so great that the luminosity of the air was invisible by contrast. The maximum distance at which phosphorescense was discernable in open air was about 8 cm. The best phosphorescent screen consisted of paper saturated with pentadecylparatatolylketone. In order to prepare it, he laid a sheet of paper upon glass and applied the fused chemical with a brush. As to the color of the phosphorescence and fluorescence of different substances, and as to the degree of luminosity outside of the vacuum tube, they were about the same as reported by Crookes when located within the discharge tube. §55. Baric and potassic and other double cyanides of platinum, common flint, glass, chalk and asaron all exhibited the same property as when exposed to ultra-violet light, that is, fluoresced or phosphoresced. Sulphide of quinine in the _solid_ state fluoresced, but not in _solution_. Petroleum spread on a piece of wood fluoresced, and also fluorescent-hydrocarbons generally. 66_a_. The cathode rays were not easily transmitted by tinfoil or glass, because the degree of phosphorescence on the screen was greatly reduced by interposing such sheets. The phosphorescense ceased also by deflecting internal cathode rays from the window by a magnet. For full treatment of the phenomena of phosphorescence, see Stokes’ experiments, described in _Phil. Trans._, 1852, Art. “Change of Refrangibility of Light.” In brief, Stokes’ theory assumes that such substances have the power of reducing the refrangibility. Example: Ultra-violet light, highly refractive, is changed to yellowish green, less refrangible, by reflection from uranium glass. 67. THE ALUMINUM WINDOW, A DIFFUSER OF CATHODE RAYS. § 63_b_. The conclusion arrived at by mounting the phosphorescent screen in different positions and at different angles as well as by observance of the gaseous luminosity, was that the aluminum window scattered the rectilinear parallel cathode rays in all directions, § 57.