As might be expected, a large number of experimenters turned their attention to the in vestigation of the nature and properties of these cathode-ray particles or negative cor puscles, and many exceedingly difficult, beauti ful and ingenious lines of research were carried out in this direction. One of the most interest ing was Sir J. J. Thompson's determination of the speed of translation of the corpuscles in the cathode ray, by a method wholly different from that of Wiechert. By the aid of a magnet he deflected the cathode stream so that for a definite time it entered an insulated hollow vessel that was connected with an electrometer, which served to measure the aggregate electri cal charge of the entering corpuscles. Inside the vessel the beam impinged upon a delicate thermoelectric couple of known thermal capac ity, by means of which the total kinetic energy of the torrent of corpuscles could be determined (in the form* of heat). The curvature of the beam, outside the closed vessel and under the influence of the magnetic field, was observed at the same time. If N is the number of corpus cles entering the closed vessel in a given time, and e is the negative electrical charge on each one of them, then Ne is the total aggregate charge on all the N corpuscles taken together. This was one of the quantities measured. Let us represent it by Q and write Q Ne. Again, if u is the velocity of the panicles (as sumed to be the same for all) and m is the mass of any one of them, the kinetic energy of each corpuscle will be imul, and the total aggre gate kinetic energy of the N corpuscles that entered the enclosure will be iNmul. This quantity, which we will denote by W (so that W=iNmie), was given by the thermoelectric couple. Finally, if H is the intensity of the magnetic field (in electromagnetic units) and r is the radius of curvature of the cathode beam where it traverses this field, we have, from general electrical principles, the relation Her. We find that it is possible, from these three equations, to eliminate N and to find the values of u and — respectively. In fact, we 2 W 2 W enhave —and— — Wh the experi QHr m—QHerr ment was perforined and the observed values of the measured quantities were substituted on the right-hand side of each equation, the value of the speed, u, proved to be about 10,000 miles (or 1.6 X 10' centimeters) per second. The value simultaneously found for (or the elec trical charge of a corpuscle, per unit of its mass) was about 10', the mass being supposed to be measured in grammes, and the electric charge expressed in absolute electromagnetic units. According to this result, the charge of the negative corpuscle, per unit of mass, is about the thousandth part of the charge ob served on the hydrogen atom, per unit of mass in ordinary electrolysis.
It was, of course, highly important to con firm these extraordinary results in as many ways as possible. Another method that sug gested itself for determining the speed of cathode-ray corpuscles depends upon the fact that a static electric field tends to deflect a moving electrified particle and cause it to de scribe a curved arc— circular or parabolic, ac cording to the conditions of the experiment. By subjecting the cathode ray, simultaneously, to a static electric field of intensity E and to a magnetic field of intensity H, it is possible, if the directions of the lines of force are properly chosen, and the respective intensities H and E are properly related, to cause the two fields to neutralize each other, so far as the deflection of the cathode ray is concerned. An application of the principles of theoretical electricity shows that if the deflection of the ray is to be zero, the two fields acting on its particles must fulfil the relation Hu, from which we obtain the very simple result, E In other words, if we find, by experiment, a combined magnetic and electroitatic field in which the cathode ray remains sensibly straight, the velocity of the particles of the ray may be found at once by merely dividing the strength of the observed magnetic field by the strength of the observed electric field. The actual ap
plication of this method involves special diffi culties, but J. J. Thomson overcame them all, and obtained numerical results indicating that the velocity u lay between 3 X 10' and 2 X 10° centimeters per second; and this, combined with the result obtained by applying the equation mu =Her, which holds when the magnetic field acts alone (r being then the radius of curvature of the cathode ray), led to the fur ther conclusion that the value of — lies between 0.7 X 10' and 0.9 X 10', if m is measured in grammes and e in absolute electromagnetic units.
It should not be inferred that all our in formation with regard to the negative corpuscle is obtained from the study of the cathode ray, because this is far from being the case. Ac cording to the views at present held, the nega tive corpuscle plays a leading part in many physical phenomena, and the study of various other departments of physics has led to con firmatory conclusions with regard to the prop erties of these corpuscles. The Zeeman effect, for example, affords a means of determining the ratio gives results that are in harmony with determinations obtained from the cathode ray. The Zeeman effect, in its simplest form, consists in the doubling of the spectral lines of substances, when the radiating source, from which the light giving the spectrum pro ceeds, is subjected to the action of a powerful magnetic field, in which the lines of force are parallel to the direction of radiation. There is much to be done in the way of clearing up our ideas of the mechanism by which radiation is effected (see RADIATION and MOLECULAR THE ORY), but for the moment let us assume that light-waves originate in the disturbances pro duced in the ether by negative corpuscles exe cuting orbital motions within the atoms of the radiating substance. The planes in which the corpuscles perform these orbital motions will, in general, be distributed equally in all possible positions, and the projections of their orbits upon any selected fundamental reference plane will be described, by the corresponding projec tions of the corpuscles themselves, equally in a clockwise and a counter-clockwise d.rection. Now if the radiating source be subjected to a strong magnetic field, the lines of force of which are parallel to the direction of the ray under consideration, the speed of the respec tive corpuscles will be differently affected, ac cording as their projections are revolving clockwise or counter-clockwise, in their orbits as projected 'upon a plane perpendicular to the lines of force. Those that are revolving in one direction will be accelerated and those that are revolving in the opposite d.rection will be retarded, in accordance with known principles in the theory of electricity and magnetism. But a difference in the periods of revolution of the corpuscles will mean a difference in the wave length of the emitted light, and hence if the magnetic field is sufficiently intense, it will cause a visible separation of the spectral lines into doublets. Lorentz, basing his calculation upon considerations of this kind, has shown that if T is the original period of the undisturbed vibration causing any given spectral line, and t is the difference in period correspond.ng to the two components into which the line is resolved by means of the magnetic field, we have I e HT= nt where e, m and H have the same significance as above, and it •-• 3.14159. . . . With the exception of e and m, all these quantities are either known or obtainable by direct observa tion; and hence the equation affords us an inde pendent means of determining the ratio of e to m. Upon performing the experiment Zeeman found values of tn — ranging from 1.4 X 10' to 1.8 X 10', which agrees fairly well with the re sults previously obtained from the study of the cathode ray.