the Intrinsic Field of a Magnet. 419 



intrinsic field cannot be regarded as simply and solely a 

 magnetic field o£ immense maguitude. 



This and other difficulties disappear if the intrinsic field 

 is treated as the combination of two fields, one a molecular 

 field, and the other a true magnetic field ; the former in 

 magnitude very large and the latter relatively small. It is 

 then assumed that thermal action operates directly on the 

 molecular field by giving rise to translatory movements of 

 the molecules, and that it only indirectly affects the magnetic 

 field by producing rotational vibrations through the mutual 

 magnetic forces of the molecular magnets, the rotational move- 

 ments so developed being a transcription .of the translational 

 movements ; on the other hand, orientations of the molecular 

 magnets which result from the application of an external 

 magnetic field cannot appreciably influence translations or 

 displacements of the molecules. 



This view of a two-fold field explains why the critical 

 temperature is lowered by an alternating magnetic field, 

 while the temperature at which the specific heat changes 

 sharply is but slightly altered ; for an alternating field 

 exciting rotational vibrations in the magnetic molecules is 

 highly effective in reducing magnetic intensity by increasing 

 the amplitude of the vibrations, and therefore a lower 

 temperature than the critical temperature is sufficient to 

 bring about the magnetic critical condition ; but, on the other 

 hand, an alternating field adds little, or a negligible amount, 

 to the energy of thermal agitation, and so the specific heat 

 is almost unaffected. 



This view also gives a reasonable account of the relations 

 of mechanical and magnetic forces, and shows why elastic 

 and magnetic qualities tend to disappear at the same high 

 temperature. 



Further, it removes a serious defect in the former statement 

 of the kinetic theory of magnetism and now allows consistent 

 values to be calculated from the ferro- magnetic equation, 

 whether the intensity of magnetization is treated as a 

 function of the temperature or a function of the applied 

 field. 



And, lastly, it gives an explanation of the abnormal rise of 

 specific heat, and the abnormally large temperature coefficient 

 of resistivity found in the ferro-magnetic metals. 



July 30th, 1921. 



2 E 2 



