52. Moore’s Experiment. Luminosity in Discharge Tube by Self-induced Currents. Trans. Amer. Inst. Elect. Eng., Sept. 20, ’93 and April 22, ’96. Several U. S. Letters Patent. Invented 1892.—During or about 1831, Prof. Henry discovered that when the circuit of a primary battery was interrupted, a self-induced current, which he called an extra current, was produced. When the circuit was closed, there was also a self-induced current, but very much feebler than that obtained on interruption. The self-induced current occurred only at or about the instant of interruption or completion. He found also that the self-induced current produced by interruption was enormously increased in E. M. F. if the circuit included a helix of very long and fine wire. It was further increased by the presence of an iron core. With one or two cells, the spark upon interruption was scarcely visible, but with a fine wire 30 or 40 feet long, an appreciable spark was obtained during interruption. With but a comparatively few cells, and with a magnet for example like a telegraph relay, the E. M. F. arose to several thousand volts at the instant of interruption. D. McFarland Moore introduced into such a circuit a Geissler tube and provided a rapid automatic interrupter. Page, Ruhmkorff and others had, at an early date, noticed the desirability, in operating Geissler tubes by secondary currents, to obtain quick interruption in the primary circuit in order to produce the best effects in the Geissler tube. Moore caused the interruptions to take place in a vacuum, so high that a disruptive electrical discharge could not pass. The break was therefore, absolutely instantaneous and complete. By this system, illustrated in diagram in Fig. 18, p. [17], he obtained all the luminous effects, actions by magnets, the sensitive state, striae and all the other phenomena heretofore noticed in Geissler tubes and some of those obtained by Tesla with his apparatus as just described. In greater detail, it will be noticed that he had a dynamo of rather low E. M. F., generally 100 volts, and a high vacuum containing a circuit interrupter operated automatically by a magnet outside like a vibrator in an electric bell. The magnet served also as the self inductive device. The magnet and interrupter were in series with each other, therefore, while the Geissler tube was in series with the magnet, and the electrodes extended either inside of the Geissler tube or remained on the outside. He performed numerous experiments on similar lines and developed the system on a large scale, whereby rooms (e.g. the hall of the Amer. So. Mech. Eng., N.Y.) have been illuminated as if by other artificial illuminants, by employing long and numerous vacuum tubes. Among several discoveries was that of the production of a bright pencil of light along the axis of a long open helix, which formed one of the internal electrodes. The Patent Office made strenuous efforts to determine the degree of novelty, assuming that some one else must have conceived the idea of employing a self-induced current to operate Geissler tubes; but nothing nearer than Poggendorff’s experiment [§ 42] could be found, and therefore the following claim (in patent 548576, Oct. 22, ’95,) was granted among a hundred or so relating to developments and details and particularly covering the vacuum interrupter. “The method of producing luminous effects, consisting in converting a current of low potential into one of high potential, by rapidly and repeatedly interrupting the low potential current in its passage through a self-inductive resistance, and passing the former current through a Geissler tube, thereby producing light within the tube.”
Edison’s Beneficent X-ray Exhibit, [§ 82], p. [71], and [§ 132], p. [126].
Calcic tungstate screen at center, sciascope near right.
CHAPTER V
53. Crookes’ Experiment. Dark Space Around the Cathode. Lect. Brit. Asso., Shef., Eng., Aug. 22, ’79.—According to Lenard (The Electr., Lond., Mar. 23, ’94) Hittorf discovered the cathode rays, and Varley, [§ 61a]., and Crookes studied them. The pressure of the residual gas was 1 M. of an atmosphere. Prof. Crookes, F.R.S., maintained the evacuated space in communication with the air pump and with an absorbent material. Before his time most experimenters worked with a vacuum not much less than 30,000 M. The first experiment is illustrated in diagram, at Fig. 6 p. [17], but the vacuum was not the highest in this type. The tube was cylindrical and was provided with electrodes at the ends. Another electrode was located at the centre and was made the cathode, while the two terminal electrodes were made the same pole; namely, the anode. Upon connecting the tube in circuit with the secondary of a large induction coil, the luminosity did not extend either continuously or in striae throughout the length of the tube. Former investigators had likewise noticed the dark space. The space and glass on each side of the central cathode were dark. The dark space extended for about one inch on each side of the negative pole. It is not intended here, any more than in former cases, to present theories in explanation further than to briefly allude to any conclusion at which the experimenter himself arrived. Crookes’ explanation of the phenomena has not been universally accepted, nor has it been proved otherwise. The knowledge of the existence of rays, now known as Roentgen rays, will assist in formulating theories upon the Crookes’ phenomena and may either confirm some of his views or overthrow them. Crookes considered that the residual atmosphere was in such a state as to be as different in its properties from gas, as gas is from liquid and liquid from solid, and therefore he named the attenuated atmosphere radiant matter, or fourth state of matter. He concluded that the remaining particles of the gas forming the radiant matter moved in straight lines over a great distance as compared with that moved through by molecules at the ordinary pressure. He called this distance the “mean free path.” If his theory is correct, this dark space is due to the fact that the molecules in motion at and near the cathode do not bombard each other and therefore do not produce the effect of light. When the motion is arrested by particles of gas themselves, within the bulb, then is light generated. The force propelling the particles from the positive pole was supposed to be less. In order to let the experiments speak for themselves, as much as possible, without being too much influenced by the opinion of the experimenter; the theory is only briefly alluded to as above, and will not be further applied in the presentation of his other experiments. In view of the radical discoveries of Lenard and Roentgen, after the installation of the Crookes phenomena, it has been the policy of the author to present all the experiments as facts for evidence in behalf of the general theories, which may be hereafter formulated independently of old theories. Therefore, the reader should bear in mind the teachings of the various experiments with the view of arriving at general principles and hypotheses.
54. Relation of Vacuum to Phosphorescence.—He started with such a high vacuum that he could not obtain any electrical discharge. [§ 25]. There was, therefore, no phosphorescence in the glass tube, whatever. The caustic potash, which had been employed to absorb the last trace of moisture and carbonic acid gas, was slightly heated, and very gradually. Then it was noticed that a current began to pass and that the glass became green, and apparently on the inner surface. As the heat continued, the green passed gradually away and was replaced by striae, which first appeared to extend across the whole diameter of the glass tube ([§ 40]) which was a long cylindrical tube, and then became concentrated toward the axial line of the tube. Finally, the light consisted of a pencil of purple. [§ 10]. When the source of heat was removed so that the moisture and carbonic acid gas could be absorbed again by the potash, the striae appeared, and then the other effects just named, only in the reversed order, until the tube acted like an infinite resistance. Phosphorescence is the correct word, because the light existed for a few seconds after cutting off the current.
55. Phosphorescence of Objects Within the Vacuum Tube.—The construction in Fig. 7, p. [17], shows how a diamond was caused to phosphoresce within a Crookes’ tube, being supported in a convenient manner in the centre of one of the tubes, while electrodes were located near the ends and were formed of disks facing the diamond. Upon connecting the disks to the respective poles of the secondary conductor, and by performing the experiment in a rather dark room, the diamond became brilliantly phosphorescent, radiating light in all directions. He experimented with many substances in this way, but found that the diamond was the best—almost equal to one candle power. In order to exhibit the phosphorescence of glass in a striking manner, he charged three small tubes simultaneously. One was made of uranium glass which radiated a green light. Another was an English glass which appeared blue, and the remaining one was German glass which phosphoresced a bright green. Notice difference with respect to light which does not perceptibly cause phosphorescence of glass. The uranium glass was the most luminous. Luminous paint, as prepared by Becquerel, and later by Balmain, which has the property of storing up light and afterwards radiating it in a dark room for several hours, became more phosphorescent in the Crookes tube than when subject to day-light. Phosphorescence of the mineral phenakite, the chemical name of which is glucinic aluminate, was blue, the emerald, crimson, and spodumene, which is a double silicate, were yellow. The ruby phosphoresced red, whatever its tint by day-light. In one tube he had rubies of all the usual tints by day-light, but they were all of one shade of red by the action of the disruptive discharge in the tube.
56. Darkness and Luminosity in Arms of V Tube. See Fig. 8, p. [17]. It will be noticed that in Fig. 6, p. [17], the tube was straight. Crookes desired to see what effect would take place in a bent tube. He therefore employed a V shaped tube, having electrodes in the ends—one in each arm. Upon causing the electrical discharge to take place through the tube, one arm was luminous and the other was dark. Whatever the E. M. F. was, the appearances remained the same. No luminosity would bend from one arm of the V shaped tube to the other. The cathode arm was always luminous and the anode dark. With a less degree of vacuum, both arms were luminous, according to early experimenters who thus brilliantly lighted tubes of the most fantastic shapes.