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LXXV. The Application of Van der Waals' Equation of 

 State to Magnetism. By J. R. Ashworth, U.Sc* 



Index to Paragraphs. 



1. Curie's experiments and views. 



2. Extension of the paramagnetic equation to include 



i'erro magnetism. 



3. The ferromagnetic equation. 



4. The critical constants and the fundamental magnetic 



constants. 



5. Corresponding states and the ferromagnetic equation. 



6. The application of the ferromagnetic equation to the 



intensity of magnetization as a function of the tempe- 

 rature. 



7. Magnitude of the intrinsic field. 



8. The kinetic theory and the ferromagnetic equation. 



9. Table of constants. 



1. TN 1895 P. Curie published his paper on the " Magnetic 

 JL Properties of Substances," and in that paper he 

 reached two important conclusions. The first was that 

 feebly magnetic substances have in general an intensity of 

 magnetization in simple inverse ratio to the absolute tempe- 

 rature in a constant field of force |. When to this is added 

 the law that the intensity of magnetization of feebly magnetic 

 or paramagnetic substances is directly proportional to the 

 strength of the field, we have a complete and simple account 

 of the behaviour of paramagnetic substances in relation to 

 field strength and temperature. If I is the intensity of 

 magnetization, calculated as magnetic moment per unit 

 volume, H the strength of the field, and T the absolute 

 temperature, we can express the two laws in the equation 



I=A? or Hj=R'T, 



where R/ is a constant the reciprocal of which is Curie's 

 constant A. The manner in which the intensity of mag- 

 netization varies in relation to field strength and temperature 

 is thus analogous to the manner in which the density of a 

 gas varies under the influence of pressure and temperature. 

 The intensity of magnetization I corresponds to the density 

 p of a gas, and the strength of the magnetic field H to the 

 pressure P applied to the gas ; the absolute temperature 

 plays the same part in both cases. We have then the analogous 

 paramagnetic and gas equations 



Hr=R'T, P--RT. 



1 P 



* Communicated bv the Author. 

 t Curie, (Euvres, pi 330. 



