352 Dr. J. R. Ashworth on the Calculation of 



Let I = Intensity of Magnetization, 

 H = Field Strength, 

 T = Absolute Temperature, 

 and R/= a constant. 



Then, if I is small compared with the saturation value (I ), 



y=E'T (1) 



Here R' is the reciprocal of Curie's constant (A) — that is 

 to say, is the reciprocal o£ the product of the susceptibility 

 into the absolute temperature. 



If, however, I becomes appreciable compared with I 

 equation (1) must be extended to express the fact that 

 I may reach a limiting value (I ) . 



When the mutual control of the magnetic molecules 

 is negligible compared with the external force the more 

 general equation is 



H 



(KH T (2) 



To change the magnetic energy from HI to HI when 

 H is constant thermal energy must be supplied which 

 may be expressed in terms of R, the gas constant, and 

 T, the absolute temperature, RT being double the energy 

 corresponding to each degree of freedom of the molecule. 



Since there are two degrees of freedom which affect the 

 magnetic moment, the mean kinetic energy under con- 

 sideration will be RT, assuming that the vibrations and 

 rotations take place with the same freedom as the translatory 

 movements of the molecules of a gas. 



Putting I = - Io at temperature T, then equation (2) 

 becomes 



5(»_i)=E'T, (3) 



J o 

 and multiplying throughout by I 2 we have 



HI (n-l)=R'TV (4) 



The left side of this equation is the kinetic energy 

 required to reduce the magnetic intensity from I to 



