99. Elster and Geitel’s Experiment. Effect of Polarized Light upon the Cathode. Berlin Akad. ’95. Nature, Lon., March 28, ’95, p. 514. Proc. Brit. Asso., Aug. 16, ’94; Aug. 23, ’94, p. 406.—The X-rays have properties similar to those of light, and have their source in electricity. Quincke discovered that light which has been polarized perpendicularly to the plane of incidence is greatly increased as to its power of penetrating metals. Elster and Geitel used the following apparatus to determine the relation between polarized light and electricity. The current varied according to the angle of incidence and the plane of polarization. The apparatus comprised the following elements: An exhausted bulb, provided with a platinum anode, and a cathode consisting of potassium and sodium, combined in the form of a liquid alloy having a bright surface of reflection. The source of light was an oxyhydrogen flame, which played upon zircon instead of lime; a lens changed the diverging rays to parallel rays, which were polarized by a Nichol prism and allowed to fall upon the cathode. The electrodes of the vacuum bulb were connected to the poles of a generator of a current of about 400 volts. “The strength, of the current was greatest when the plane of polarization was perpendicular to the plane of incidence—i.e., when the electric displacements constituting light, took place in the plane of incidence, and when the angle of incidence was about 60°, i.e., the polarizing angle of the alloy itself.” Prof. Sylvanus P. Thompson confirmed these results by experiment. The rate of discharge was greatest, he said, when the plane of polarization was such that the Fresnellian vibration “chopped into” the surface. Polarized light, he reminded them, produced similar results upon selenium.
Although the domain of this book is necessarily limited to the consideration of phenomena connected with the internal and external energy of a discharge tube, yet if any other one subject is of special interest and utility in connection with the consideration of X-rays, it is that concerning the relation between the electric discharge and light, which has been thoroughly studied only during the past few years, and the accounts of the researches recorded in various periodicals and academy papers. Those readers, however, who desire to study this exceedingly interesting and novel branch of science, which in connection with the action of the internal cathode rays and X-rays upon electrified bodies, tends to uphold Maxwell’s theory as developed by mathematics and based upon early known facts and predicted discoveries, may find volumes upon this subject by referring to the citations below, named by Mr. N. D. C. Hodges and obtained by him by a search in the archives of the Astor Library. Of especial interest are those of Branly, [§ 99I], [99J], [99Q], [99S], [99T]. Some notion as to the contents of the citations are given here and there.
99A. Koch’s Experiment. The Loss of Electricity From a Glowing Electrified Body. Wied. Ann., XXXIII., p. 454, ’88.
99B. Schuster and Anpenius’ Experiment. The Influence of Light on Electrostatically Charged Bodies. Proc. R. So., Lon., LXII., p. 371, ’87; Proc. Swedish Acad., LXIV., p. 405, ’87.—Many recent periodicals have set forth that ultra-violet light will discharge only negatively charged bodies. While this is practically or sometimes the case, yet these experimenters found that a positive charge was dissipated very slowly. They confirmed the results that the ultra-violet rays played the principle part in the removal of a negative charge. Polishing the surface accelerated the action. [§ 99], near beginning.
99C. Righi’s Experiment. Some New Electric Phenomena Produced by Light. Note 2-4, Rend. R. Acad. die Lincei, May 6, 20, and June 3, ’88.
99D. Righi’s Experiment. Some New Electric Phenomena Produced by Illumination. Rend. R. Acad. die Lincei. VI., p. 135, 187, ’88.—Confirmation of the results of other physicists, and a quantitative measurement determining that the E. M. F. between copper and selenium was increased 25 per cent. by illumination by an arc light. The selenium was in the form of crystals mounted upon a metal plate.
99E. Stolstow’s Experiment. Actino-Current Through Air. C. R., CVI., pp. 1593 to 95, ’88.—Liquids tested. Greatest absorbents of active rays most quickly discharged.
99F. Righi and Stolstow’s Experiments. Kind of Electric Current Produced by Ultra-Violet Rays. C. R., CVI, pp. 1149 to 52, ’88.—The discharge was accelerated by using a chemically clean surface. The burning of metals, for example, aluminum, zinc or lead in the arc light increased the discharging power.
99G. Bichat & Blondot’s Experiment. Action of Ultra-violet Rays on the Passage of electricity of Low Tension through Air. Comptes Rendus. CVI, pp. 1,349 to 51. ’88.—They employed arc lamps whose carbons had aluminum cores.
99H. Nacarri’s Experiment. The Dissipation of Electricity through the Action of Phosphorous and the Electric Spark. Atti di Torino. XXV, pp. 252 to 257. ’90.—The loss of charge was eighteen times less rapid in the dark through the air in a bottle, than when a piece of luminous phosphorous was placed in the bottle. The introduction of turpentine, which checked the glowing of the phosphorous, retarded the loss of charge.