The reduction of temperature of the electrode he attributed to its volatilization. Without actually testing the rays with a fluorescent screen or photographic plate, he could always know their presence by the relative temperatures of the phosphorescent spot and the electrode, for when the latter was at a low temperature and the former at a high temperature, X-rays were sure to be strong.
From the fact that the vacuum became higher and higher by the means stated, he was very much inclined to believe that there was an expulsion of material particles through the walls of the bulb. When these particles which were passing with very great velocities struck the sensitive photographic plate they should produce chemical action. He referred to the great velocity of projected particles within a discharge tube, pages [46] and [47], and to Lord Kelvin’s estimate upon the same, and reasoned that with very high potentials, the speed might be 100 km per second. The phenomenon indicated, he said, that the particles were projected through the wall of the tube and he entered into an elaborate discussion on this point. He referred to his own experiment of causing the rays from an electrode in the open air to pass directly through a thick glass plate. [§ 13]. He performed an experiment also of producing a blackening upon a photographic plate apparently by the projected particles, an electrical screen being employed to prevent the formation of sparks. [§ 35]. which as well known will cause chemical action upon the plate. No stronger proof as to the expulsion of material particles could be desired than an operation in which the eyes can see for themselves that such an action must have taken place. Usually he was troubled by the streamers (cathode rays) from the electrode suddenly breaking the glass of the discharge tube. This occurred when the spot struck was at or near the point where the same was sealed from the pump. He arranged a tube in which the streamers did not strike the sealing point, but rather the side of the tube. It was extraordinary that a visible but fine hole was made through the wall of the tube, and especially that no air rushed into the vacuum. On the other hand, the pressure of the air was overcome by something rushing out of the tube through the hole. The glass around the hole was not very hot, although if care were not taken, it would become much hotter, and soften and bulge out, also indicating a pressure within, [§ 27]. greater than the atmospheric pressure. He maintained the punctured tube in this condition for some time and the rarefaction continued to increase. As to the appearances, the streamers were not only visible within the tube, but could be seen passing through the hole, but as the vacuum became higher and higher, the streamers became less and less bright. At a little higher degree of vacuum, the streamers were still visible at the heated spot, but finally disappeared.
This electrical process of evacuating varies in its rapidity according to the thinness of the glass. Here again he noted the application of his theory in that an easier passage was afforded for the ions. [§ 47]. A few minutes of operation produced through thin glass, a vacuum from very low to very high, whereas, to obtain the same vacuum through much thicker glass over 1/2 hour was necessary. Again with a thick electrode the time required was much greater. The small hole was not always visible and it was thought that the material went through the pores. The result obtained by the following experiment tends to uphold Mr. Tesla’s emission theory.
139a. Lafay’s Experiment. Giving to X-rays the Property of Being Deflected by a Magnet by Passing Them Through a Charged Silver Leaf. Comptes Rendus, March 23, ’96 and April 7, 13, 27, and L’Ind. Elec., April and May ’96. From trans. by Louis M. Pignolet. He placed at about .5 cm. below a discharge tube, a lead screen pierced by a slit 2 mm. wide; and 0.04 m. lower, a second lead screen having a slit 5 mm. wide completely covered by an extremely thin leaf of silver. Opposite the silver leaf and exactly in the axis of the slit, was fixed a platinum wire 1.5 mm. diameter. Thus, the rays which passed successively through the two slits projected a shadow of the wire on a photographic plate below.
When the silver leaf was connected to the negative pole of the induction coil that excited the tube, the rays, which had become electrified ([§ 61b], p. [47]) bypassing through the leaf, were deflected by a magnetic field of about 400 L. G. S. units, whose lines of force were parallel to the slit. The direction of the deflection was determined by the same law as that of the deflection by a magnetic field of the cathode rays in the interior of a discharge tube. [§ 59]. When the silver leaf was not connected to the coil, no deflection was produced. [§ 79].
To double the apparent deflection, one part of the slit was covered by a lead plate during the first half of the experiment. The lead plate was removed and placed over the other part of the slit, and the direction of the magnetic field reversed during the last half of the experiment. Thus the distance on the sciagraph between the two parts of the wire, was double the deflection produced by the magnetic field.
The deflection was in the same direction when the silver leaf was connected to the negative pole of a static electric machine, but was in the opposite direction when the leaf was connected to the positive pole of the machine. The test was criticised in the scientific press, and, therefore, in order to be certain that the deflections observed were not due to the combined effects of the electro-magnet which produced the magnetic field and the electric field of the charged silver leaf, the experiments were modified. To remove this uncertainty, the electrified rays were caused to enter a grounded Faraday cylinder (see figure at E. F. G. H., p. [47]), through a small opening, before passing between the poles of the electro-magnet. The deviations which were recorded on a photographic plate in the box were the same as before.
Additional experiments showed that the deflections by the magnetic field took place as well when the rays were electrified, after their passage through another magnetic field, as before. Lafay continued the experiments in great detail and by many control tests, and he took accurate measurements and followed the suggestions of others. It would be well for those who have facilities to repeat these most interesting and important researches, to determine for themselves some satisfaction.
It is of interest to note that an American, Paul A. N. Winand, (Mem. Amer. Inst. Elect. Engs.), in the absence of facilities for experimenting, proposed (Elect. World, N.Y., June 6, ’96) to interpose a hollow sphere, which had high potential, in the path of X-rays, and to learn in what manner, if any, the rays are influenced. He argued that it would seem natural that, inasmuch as the rays produce a discharge, there should be a reaction of the charged surface upon the rays.
It is evident that if any one repeats these experiments, expert manipulation is required.