Mat 20, 1921] 



SCIENCE 



471 



that either is true at low temperatures. There 

 is a general agreement between theory and 

 experiment. The trend of the experimental 



FiQ. 4. 



Pig. 5. 



curve can not be explained by the presence 

 of iron, as the positive susceptibility of the 

 iron would become less with temperature 

 increase. 



We come now to the second case, in which 

 the magneton has a true axis of figure and 

 an essentially permanent angular momentum 

 about this axis, and therefore a magnetic 

 moment in the direction of this axis, un- 

 changeable by collisions. On account of this 

 permanent magnetic moment and angular 

 momentum, paramagnetism results very much 

 as in the theory of Voigt already presented; 

 and on account of the slight diminution of 

 this angular momentum in the magnetic field 

 and on account of the rotation of the mag- 

 neton about the other axes brought about or 

 modified by the thermal agitation in accord- 

 ance with the law of equipartition, diamag- 

 netism results and is superposed upon the 

 paramagnetism. 



This diamagnetism does not appear in 

 Langevin'a theory, because instead of a per- 

 manently rotating magneton he assumed a 

 permanent magnet without angular momen- 

 tum about the axis except as produced by 

 thermal collisions. Langevin, however, as- 

 sumed that Weber's diamagnetism was super- 

 posed upon the paramagnetism, and this cor- 

 responds in part to the diamagnetism of 

 Gans's theory. 



Returning to the results of Gans's statis- 

 tical treatment for the case of the magneton 

 in permanent rotation about a unique axis, 

 we find that the susceptibility is a function 

 of both field strength and temperature. It 



may even be positive at lower intensities or 

 temperatures, and negative at higher. 



Isothermals for different temperatures be- 

 tween the susceptibility G and the magnetic 

 intensity h are shown in Fig. 6, and isody- 

 namics for different intensities h between the 

 susceptibility G and the temperature 6 are 



Pig. 6. 



shown in Fig. 7. Thus while diamagnetism 

 may exist without paramagnetism, paramag- 

 netism is always accompanied by diamag- 



FiQ. 7. 



netism, as on all other theories. In weak 

 fields and at low temperatures the paramag- 

 netism may prevail; but as the temperature 

 and field strength increase it goes over into 

 diamagnetism. 



A transition from paramagnetic to diamag- 

 netic susceptibility, whatever may be the ex- 



I 



