90 MR- A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 



The crystallization of a diamagnetic substance may be regarded as accompanied by 

 the production of a spontaneous local intensity of magnetization. We have up to the 

 present regarded the molecular field as a magnetic field, and a close analogy has been 

 found between the phenomena shown by ferro-magnetic and diamagnetic substances. 

 The question as to how far we are justified in regarding the molecular fields as 

 magnetic fields will be discussed in 8. 



(5) ON THE STRESSES AND ENERGY ASSOCIATED WITH THE MOLECULAR FIELD. 



In the previous work evidence has been given which shows that the forces 

 associated with a diamagnetic crystalline structure are exceedingly large, and 

 therefore the potential energy of the crystalline state will be considerable. If 1 1 be 

 the local magnetic moment which in conjunction with the local molecular field H c | 

 binds one molecule to another in the crystalline structure, and if all such elementary 

 systems (each system consisting of the adjacent parts of a pair of molecules which 

 are bound together by the local forces) are independent, then the energy possessed 

 by 1 c.c. of the substance in virtue of a particular crystalline grouping may be 

 written 



& ' -!H e |. 



Let n be the number of molecules per cubic centimetre. Then 



where H c corresponds to the molecular field in ferro-magnetism. If we put n. 

 and H c = a' c l, we find for the energy associated with 1 gr. of the substance 



Here a! c is the constant of the molecular field, I the aggregate of the local intensity 

 of magnetization per unit volume, and p c the density of the substance. This is the 

 amount of potential energy which the molecules contained in 1 gr. possess in virtue 

 of their grouping, and is additional to the energy possessed by 1 gr. of the liquid. 

 "We may treat the crystalline substance as a fluid whose molecules do not influence 

 one another, providing the energy term represented by (13) is superposed upon any 

 energy which 1 gr. of the fluid may possess. Therefore if the crystalline structure 

 be submitted to a magnetic field H, the potential energy associated with 1 gr. may 

 be written 



.r], ......... (14) 



'Pi 



where k, and Pl are the susceptibility and mass per unit volume of the liquid. Let us 

 now compare this with the expression given by LARMOR* for the potential energy per 



* ' Roy. Soc. Proc.,' A, vol. 52, p. 63, 1892. 



