Fig. 1.
61b. Perrin’s Experiment. Cathode Rays Charged With Negative Electricity. Corresponding Positive Charges Propagated in the Reverse Direction and Precipitated upon the Cathode. Comptes Rendus, CXXI., No. 20, p. 1130; The Elect., Lon., Feb. 14, ’96, p. 523.—Jean Perrin’s object was to discover whether or not internal “Cathode rays were charged with negative electricity.” That they were had often been assumed by others, namely, Prof. J. J. Thomson, who considered cathode rays as due to negatively charged matter moving at high speed. [§ 61b]. Again, Prof. Crookes, principally, and others, showed that they were possessed of mechanical properties and that they were deflected by a magnet. [§ 59]. Perrin called attention to the above investigations and also alluded to the theoretical considerations of Goldstein, Hertz and Lenard, who favored the analogy of cathode rays to light—whose phenomena are well answered by the accepted theory concerning assumed etherial vibrations, which, in both cases, have rectilinear propagation, [§ 57], excite phosphorescence, [§ 54] and [55], and produce chemical action upon photographic plates. Great ingenuity was displayed, as might be expected, in the manner in which Jean Perrin proved the proposition named in the title of this section, at the Laboratory of the École Normale and also in M. Pallet’s Laboratory. First, therefore, let the elements of the discharge tube be thoroughly understood. As usual, the disk N is the cathode, referring to accompanying Fig. [1]. A, B, C, D, is a metal cylinder having a small opening at the right hand end toward the cathode. Concentrically, is a similar cylinder, acting as an electrical screen and having a like opening similarly located as indicated. It corresponds to and plays the part of the Faraday cylinder, being connected to earth. The principle involved in this apparatus was based upon the laws of influence, which permitted him to ascertain the introduction of electric charges within a conducting envelope, and to measure such charges. During the discharge, the cathode rays were propagated from the cathode to and within the cylinder A, B, C, D, which immediately and invariably became charged with negative electricity. To prove that the charge was due to the cathode rays, he deflected them away from the opening in the protecting cylinder E, F, G, H. The cylinder was not under these circumstances charged, the rays being outside. He went further and made some quantitative analysis in a rough way to begin with. He related: “I may give an idea of the amount of the charges obtained when I state that with one of my tubes, at a pressure of .001 m. of mercury, and for a single interruption of the primary coil, the cylinder A, B, C, D, received sufficient electricity to bring a capacity of 600 C. G. S. units to a potential of 300 volts.” Upon the principle of the conservation of energy, he was induced, he said, to search for corresponding positive charges. “I believe I have found them in the very region where the cathode rays are generated, and that they travel in the reverse direction and precipitate themselves on to the cathode.” He verified this corollary by means of a modified feature of the apparatus shown in Fig. [2]. The construction was the same except that there was a diaphragm having a perforation β´ within the protecting cylinder and opposite the smaller cylinder exactly as indicated, so that the positive electricity which had entered through β could only act on the cylinder A, B, C, D, by traversing also the hole β´. “When N was the cathode, the rays emitted traversed the two apertures at β and β´ without any difficulty, and caused the gold leaves of the electroscope to diverge widely. But when the protecting cylinder was the cathode, the positive flux, which, as was shown by a previous experiment, enters by the aperture β, did not succeed in separating the gold leaves, except at very low pressures. If we substitute an electrometer for the electroscope we shall see that the action of the positive flux is real, but that it is very small and increases as the pressure decreases.”
Fig. 2.
He inferred that: “These results, taken as a whole, do not appear to be easily reconcilable with the theory that the cathode rays are ultra-violet light. On the contrary, they support the theory that attributes these rays to radiant matter, [§ 54], near centre, a theory, which may at present, it seems to me, be enunciated as follows: In the vicinity of the cathode the electric field is sufficiently strong to tear asunder into ions some of the molecules of the residual gas. The negative ions start off toward the region where the potential increases, acquire a considerable velocity, and form cathode rays; their electric charge, and consequently their mass (at the rate of one gramme equivalent per 100,000 coulombs) is easily measured. The positive ions move in the reverse direction; they form a diffused tuft, susceptible to magnetism, but are not a regular radiation.”
61c. Zeugen. Comptes Rendus, Jan. 27, 1896.—In a note regarding the experiments of Roentgen, called attention to his own communications to the Academie des Sciences in February and August 1886, describing his photographs of Mt. Blanc taken in the night by the invisible ultra-violet rays. This note is entered as many newspapers reported the photograph to be due to cathode rays, imagine the intense phosphorescence upon a screen at the top of the mountain, if such were the case.
62. Goldstein’s Experiment. Phosphorescence of Particular Chemicals by Cathode Rays. Nature, Lon. Feb. 21, ’95, p. 406. Weid. Ann., No. II, ’95.—Lithium chloride when acted upon by cathode rays, phosphoresced to a dark violet color or heliotrope, which it retained for some time in a sealed tube. Chlorides generally and other haloid salts of potassium and sodium showed similar effects. The colors were superficial and could be driven away rapidly either by heating or the action of moisture.
63. Kirn’s Experiment. Spectrum of Post Phosphorescence of Discharge Tubes. Wied. Ann., May, ’94. Nature, Lon. June 7, ’94, p. 131.—Carl Kirn compared the spectra of the phosphorescence of a vacuum bulb, during and immediately after the discharge. The details are as follows: The spectrum of the after-glow, [§ 54], at end and 22, was found to be continuous. In this connection, see a plate showing different kinds of spectra, for example, Ganot’s Physics, frontispiece. The spectrum shortened from both directions to a band between the wave lengths of 555 and 495µµ. The spectrum then continued to grow shorter and shorter until it disappeared at the line E, which is the position of the greatest luminosity of the solar spectrum. For experiments on spectrum, see Fraunhofer in Gilbert’s Ann., LVI. During the discharge, the spectroscope showed a line spectrum corresponding very closely to those of carbonic acid gas and nitrogen. Some authorities had suggested that perhaps the after phosphorescence and the beginning of the incandescence of a solid body, were the same kind of light, but this experiment shows that such is not the case, unless some relation exists on the ground that the two phenomena are exactly opposite to each other, and it confirms similar results obtained by Morrin and Riess. The result indicates that the nature of the phenomenon is not identical in all respects with light produced at a high temperature.
63a. 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.
63b. 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. Ann., vol. 48, p. 785.