118. EDISON’S EXPERIMENTS. CHARACTERISTICS OF DISCHARGE TUBE, PHOTOGRAPHIC PLATES, ELECTRICAL APPARATUS, FLUORESCENCE, ETC. _Elec. Eng._, N.Y., Feb. 19, ’96; Mar. 18 and 25; Apr. 1, 8, 15 and 29, ’96. X-RAYS BEGIN BEFORE STRIAE END.—The reader may remember a former section, § 10, pointing out that striae were usually obtainable without very high vacua, and that phosphorescence of the glass occurs only with high vacua. § 54. In carrying the vacuum up higher and higher, Edison observed that feeble Roentgen rays were detected before the striae ceased. Prof. Elihu Thomson independently performed a like experiment and found that the Roentgen rays could be obtained even when the vacuum was so low as to produce striae. (_Elec. Eng._, N.Y., Apr. 15, ’96.) Victor Chabaud and D. Hurmuzescu also obtained X-rays from a vacuum .025 mm., being lower than Crookes employed, which was at a maximum .001 mm. (_L’Industrie Elect._, Paris, May 25, ’96. From trans. by Louis M. Pignolet.) 119. REASON WHY THIN WALLS ARE BETTER THAN THICK. X-RAYS AND POST-PHOSPHORESCENCE.—This may be understood by explanation of the discharge tube in Fig. 1. In one experiment, the portion struck by the cathode rays, namely B, was made 1/8 inch thick. It became soon hot and very luminous and melted, § 61, but the X-rays were weak. When blown thin, (§ 83) however, the glass remained cool and the X-rays were much stronger. What is known on the market as German glass (phosphoresces green, § 55, at centre) was found more permeable than lead glass, the thickness of the walls being the same in both cases. There were no lingering X-rays from after-phosphorescence, (§ 54, at end) or, if any, could not be detected by the sciascope. The photographic test would be objectionable because of the brief duration. Prof. Battelli and Dr. Garbasso, of Pisa, made a very _sensitive_ test in this connection, proving by the discharge of an electrified body (§ § 90 and 90_a_) that feeble X-rays were emitted after the current was cut off from the discharge tube. (From trans. by Mr. Pignolet.) [Illustration: DISCHARGE TUBE, FIG. 1. § 119. DISCHARGE TUBE, FIG. 3. § 120. ] 120. TO PREVENT PUNCTURE OF THE DISCHARGE TUBE BY SPARKS.—In the illustration, Discharge Tube Fig. 2. shows a suitable type. It is drawn to scale, showing the correct proportion of the length to the diameter. The shaded ends represent tinfoil on the outside and connecting with the leading-in wires, the same preventing puncture of the glass by the spark. They may be caused to adhere by shellac or similar glue. In place of the metallic coating detached supplementary electrodes may be employed, as seen in the illustration marked “Discharge Tube Fig. 3.” The power of the X-rays was increased, being due, it was thought, to the fact that the construction embodied the combination of internal and external electrodes. § 121.