714 Dr. J. R. Ashworth on the Application of 



the ferromagnetic metals behave correspondingly when the 

 intensity of magnetization is treated as a function of the 

 absolute temperature, and this result leads to the conclusion 

 that there is a molecular magnetic mechanism common to 

 the ferromagnetic elements, and consequently that there is a 

 general magnetic equation applicable to all of them. 



The equation written above may be taken as a first step 

 towards an expression which shall represent the behaviour 

 of any ferromagnetic body the magnetism of which is a 

 function of the field and the temperature. 



3. The investigation of the magnitude of /(I) and the 

 form it assumes becomes now of importance in applying the 

 equation to ferromagnetic properties. 



If the continuity of states is accepted then R' must be 

 equal to the reciprocal of Curie's constant in the ferro- 

 magnetic as well as in the paramagnetic state. The value 

 of this constant for iron, nickel, and cobalt is known, and 

 this allows an estimate of the magnitude of the intrinsic 

 field to be made. When I and H are expressed in the usual 

 units and T is in absolute degrees then H t = /(I) is easily 

 found to be of the order of 10 7 gausses. For example, 

 R/ = 3*7 for iron and the product R/T at ordinary tempera- 

 tures is nearly 10 3 ; at higher intensities I -=- — j J is of the 



order 10 ~ 4 , and therefore, inserting these values in the equa- 

 tion, we have (H + HJ x 10~ 4 = 10 3 , hence H t is of the order 

 10 7 gausses. The intrinsic field for nickel and cobalt can 

 be shown to be of the same order of magnitude from a 

 knowledge of R/ for each of these metals. 



It might be thought that the form which /(I) assumes 

 would be determined by supposing the intrinsic field to be 

 derived from the intensity of magnetization in the same 

 way as the external field of a magnet is derived from its 

 magnetization. This would make the intrinsic field directly 

 proportional to the first power of the intensity of magneti- 

 zation. The experimentally determined shape of the curves 

 of I=/(T), however, does not support this supposition, and 

 moreover, an equation in which the intrinsic field is treated 

 as proportional to the first power of the magnetic intensity 

 would be incapable of representing the double inflexion which 

 curves of 1=/ (T) exhibit on passing through the critical 

 temperature. 



In place of this hypothesis we may try if the intrinsic 

 field is proportional to the second power of I, and put 

 H; = a'I 2 , where a' is a constant. This makes the ferro- 

 magnetic equation of the same form as Van der Waals' 



