But it was J. J. Thomson[26] who in 1897 first introduced a more reliable method of determining this ratio, namely, one which combines a measurement of the magnetic deflectability of a beam of cathode rays with the electrostatic deflectability of the same beam. The value which he obtained, namely, electromagnetic units, was nearly a thousand times the value of for the hydrogen ion in solutions. Also since the approximate equality of in gases and solutions meant that was at least of the same order in both, the only possible conclusion was that the negative ion which appears in discharges in exhausted tubes has a mass, i.e., an inertia, only one-thousandth of the mass of the lightest-known atom, namely, the atom of hydrogen. Later more accurate experiments have fixed the correct value of for cathode rays at . Furthermore, J. J. Thomson and after him other experimenters showed that for the negative carrier is always the same whatever be the nature of the residual gas in the discharge tube. This was an indication of an affirmative answer to the sixth question above—an indication which was strengthened by Zeeman’s discovery in [Pg 43] 1897 of the splitting by a magnetic field of a single spectral line into two or three lines; for this, when worked out quantitatively, pointed to the existence within the atom of a negatively charged particle which had approximately the same value of . The study of for the positive ions in exhausted tubes was first carried out quantitatively by Wien,[27] and was later most elaborately and most successfully dealt with by J. J. Thomson[28] and his pupils at the Cavendish Laboratory. The results of the work of all observers up to date seem to show quite conclusively that for a positive ion in gases is never larger than its value for the hydrogen ion in electrolysis, and that it varies with different sorts of residual gases just as it is found to do in electrolysis. In a word, then, the act of ionization in gases appears to consist in the detachment from a neutral atom of one or more negatively charged particles, called by Thomson corpuscles. The residuum of the atom is of course positively charged, and it always carries practically the whole mass of the original atom. The detached corpuscle must soon attach itself, in a gas at ordinary pressure, to a neutral atom, since otherwise we could not account for the fact that the mobilities and the diffusion coefficients of negative ions are usually of the same order of magnitude as those of the positive ions. It is because of this tendency of the parts of the dissociated atom to form new attachments [Pg 44] in gases at ordinary pressure that the inertias of these parts had to be worked out in the rarefied gases of exhausted tubes.