When an electrical discharge is passed through a high-vacuum tube, invisible rays are emitted from the kathode, generally with the production of a greenish-yellow fluorescence where they strike the glass walls of the tube. These rays are called “kathode rays.” At one time they were regarded as waves in the ether, but it was shown by Sir William Crookes that they consist of small electrically charged particles, moving with a very high velocity. Sir J. J. Thomson was able to determine the ratio of the charge carried by these particles to their mass or inertia; he found that this ratio was constant whatever gas was contained in the vacuum tube, and much greater than the corresponding ratio for the hydrogen ion (electrically charged hydrogen atom) in electrolysis. By a skilful method, based on the fact discovered by Mr. C. T. R. Wilson, that charged particles can serve as nuclei for the condensation of water-vapour, he was further able to determine the value of the electrical charge carried by these particles, which was found to be constant also, and equal to the charge carried by univalent ions, _e.g._, hydrogen, in electrolysis. Hence, it follows that the mass of these kathode particles must be much smaller than the hydrogen ion, the actual ratio being about 1 : 1700. The first theory put forward by Sir J. J. Thomson in explanation of these facts, was that these kathode particles (“corpuscles” as he termed them) were electrically charged portions of matter, much smaller than the smallest atom; and since the same sort of corpuscle is obtained whatever gas is contained in the vacuum tube, it is reasonable to conclude that the corpuscle is the common unit of all matter. Proof that the Electrons are not Matter. § =80.= This eminent physicist, however, had shown mathematically that a charged particle moving with a very high velocity (approaching that of light) would exhibit an appreciable increase in mass or inertia due to the charge, the magnitude of such inertia depending on the velocity of the particle. This was experimentally verified by Kaufmann, who determined the velocities, and the ratios between the electrical charge and the inertia, of various kathode particles and similar particles which are emitted by compounds of radium (see §§ 89 and 90). Sir J. J. Thomson calculated these values on the assumption that the inertia of such particles is entirely of electrical origin, and thereby obtained values in remarkable agreement with the experimental. There is, therefore, no reason for supposing the corpuscle to be matter at all; indeed, if it were, the above agreement would not be obtained. As Professor Jones says: “Since we know things only by their properties, and since all the properties of the corpuscle are accounted for by the electrical charge associated with it, why assume that the corpuscle contains anything but the electrical charge? It is obvious that there is no reason for doing so.