63_a_. DE METZ’S EXPERIMENT. CHEMICAL ACTION IN THE INTERIOR OF THE DISCHARGE TUBE. INTERNAL CATHODE RAYS. _L’Ind. Eler._, May 10, ’96, and _Comptes Rendus_, about April, ’96. Translated by Louis M. Pignolet. He used a cylindrical discharge tube divided into two halves which fitted together by an air-tight ground joint. In one-half were the anode and the cathode; in the other half was the holder containing the sensitive paper or films. The holder was exposed to the direct action of the cathode rays and was closed by a cover of cardboard or sheet aluminum. The objects to be photographed were placed between the cover and the sensitive film or paper. The tube was connected to a Sprengel pump which maintained its vacuum during the experiments. In this way, twelve photographs were taken from which it appeared that cathode rays, like X-rays, penetrate cardboard and aluminum, but are stopped by copper (1.26 mm.) and platinum (0.32 mm.). Poincaré, in a note in the same publications as the foregoing, criticised the results of the experiments of De Metz, claiming they did not prove irrefutably that cathode rays possessed the essential properties of X-rays, for the cathode rays in impinging on the cover of the holder would generate X-rays, § 91, which would give the results obtained. Poincaré did not deny the fact. 63_b_. HERTZ’S EXPERIMENT. THE PASSAGE OF CATHODE RAYS THROUGH THIN METAL PLATES WITHIN THE DISCHARGE TUBE. DIFFUSION. _Wied. Ann._, N. F. 45; 28, 1892. Contributed by request, by Mr. N. D. C. Hodges of the _Hodges Scientific News Agency_, N.Y. Found in records at Astor Library.—A piece of uranium glass was covered partly on one side (which he calls the front side) with gold-leaf, and on the gold leaf were attached several pieces of mica. This front side was then exposed to cathode rays. So long as the exhaustion had not proceeded far, and the cathode rays filled the whole tube with a blue cone of light, only the portion of the uranium glass outside the gold-leaf screen showed any phosphorescence. But as soon as the exhaustion had progressed far enough, and the light began to disappear, the genuine cathode rays struck the covered glass, and the phosphorescence manifested itself behind the gold-leaf. When the cathode rays were fully developed, the gold-leaf hardly had any effect, while the mica cast deep black shadows. The same experiment was tried with silver-leaf, aluminum and alloys of tin, zinc and copper. Aluminum showed the best results; sheets which allowed no light to pass, allowing the cathode rays free passage. The rays after their passage through the metal screens did not continue their straight course, but seemed to be diffused much as light is diffused by passing through a cloudy medium. In this connection reference is made to the work of Goldstein, who had noticed also the reflection of “electric” rays. _Wied. Ann._, N. F. 15; 246, 1882. In 1893, Goldstein published further accounts concerning actions in discharge tube. _Wied.