Mat 20, 1921] 



SCIENCE 



469 



of energy, However, Thomson has concluded 

 that paramagnetism may result, and Voigt 

 that either paramagnetism or diamagnetism 

 may result, according to circumstances. But 

 the conceptions they have presented of the 

 manner in which these results may be brought 

 about do not seem probable, and have not 

 gained wide acceptance. 



Voigt and, after him,, Lorentz and Gans,' 

 have examined the behavior in a magnetic 

 field of magnetic elements, or magnetons, con- 

 sisting of homogeneous uniformly charged 

 solids or symmetrical electron systems, in 

 rotation, and have reached interesting and 

 important conclusions. 



One of the most important cases is that 

 of a magneton which may be treated as a 

 solid of revolution, with initial angular 

 velocity greater than eH/2in about the unique 

 axis. In this case in accordance with class- 

 ical electromagnetic theory, the rotation pro- 

 ceeds undamped about the unique axis, while 

 it is damped about the other (equal) axes, 

 and the action of the field on the magneton 

 is as follows: When the field is applied, pre- 

 cession of the magneton's axis about the 

 direction of the field begins, accompanied by 

 nutation. The nutation is damped out by 

 dissipation or radiation, and the precession is 

 retarded for the same reason. Hence the 

 direction of the axis of the magneton gradu- 

 ally approaches coincidence with the direction 

 of the field, when it is in stable equilibrium. 

 During this process the velocity of rotation 

 diminishes slightly, the motion being affected 

 as in the case of the electricity in Weber's 

 molecular grooves. 



If there are N such magnetons in the unit 

 of volume, and if the demagnetizing and 

 molecular fields and the upsetting effect of col- 

 lisions are negligible, all the magnetons will 

 ultimately become oriented with their axes 

 in the direction of the magnetic field. In this 

 case the moment of unit volume will be 

 J eNC ( eH\ 



when e is the charge of the magneton, C its 

 moment of inertia about the axis of per- 

 » Gott. Nachr., 1910, p. 197. 



manent rotation, u its angular velocity about 

 this axis, and E the intensity of the applied 

 field. 



The first and principal term is entirely 

 independent of H. The orientation is, of 

 course, produced by the magnetic field, but 

 only the time taken to arrive at the steady 

 state is affected by its magnitude. The second 

 term is a diamagnetic term, and arises from 

 the fact that owing to the change of flux 

 through the magneton during the process of 

 its orientation its velocity is decreased, just 

 as in the case of the Weber-Langevin theory. 



In this case we have, except for the small 

 diamagnetic term, which vanishes with the 

 intensity, saturation for even the weakest 

 fields; and we have less nearly complete 

 saturation for stronger fields. 



When collisions are not absent, a magneton's 

 axis will be repeatedly deflected in its ap- 

 proach toward coincidence with the direction 

 of the field, and the intensity of magnetiza- 

 tion will not reach saturation; but it will in- 

 crease with the field strength, being greater 

 for a given field strength, the greater the 

 mean time between collisions and the weaker 

 the molecular and demagnetizing fields. In- 

 crease of temperature, shortening this time 

 between collisions, and increasing their vio- 

 lence, will, if the magnetons remain un- 

 changed, thus diminish the magnetization for 

 a given field strength. 



The precessional process described above is 

 doubtless similar in a general way to the 

 process by which in every case in paramag- 

 netic and ferromagnetic substances the mag- 

 netons are aligned more or less completely 

 with the magnetic field. 



The exceedingly interesting ring electroa 

 recently proposed by A. L. Parson and exten- 

 sively applied by him and others to a wide 

 range of chemical and physical phenomena, is 

 a special case of Voigt's magneton, and will 

 be discussed by one of my colleagues. 



Bearing in mind that, on the electron 

 theory, the molecule or magneton must, with 

 Voigt, be treated as a gyroscoi)e and can not 



