Manchester Memoirs^ Vol, Iviii. (1914), No. II. 



XI. Note on the Intrinsic Field of a Magnet. 



By J. R. ASHWORTH, D.Sc. 

 (^Cojiwuiuicated by Dr. George Hickling, F.G.S.) 

 {Received aitd read May 12th, igi^.) 



The researches of P. Curie have shewn that the 

 magnetic properties of the ferro-magnetic bodies above 

 their critical temperatures, the intensity of magnetisation 

 then being very feeble, may be represented by an equation 

 which is exactly analogous to the gas equation, in which 

 the gas pressure is replaced by the strength of the applied 

 field, the gas density by the intensity of magnetisation, 

 and the gas constant by a constant which, in the magnetic 

 equation, depends upon the nature of the magnetic 

 material. 



Curie further showed that a ferro-magnetic body in 

 passing through the critical temperature from the state 

 of strong magnetism into the state when the gas equation 

 applies behaves in general like a fluid in passing from 

 the liquid to the gaseous state. 



In order to develop this line of thought I have 

 suggested the application of an equation to ferro- 

 magnetism which is analogous to Van der Waals' equation 

 to fluids.' 



Van der Waals extends the gas equation by introducing 

 a mutual attraction between the molecules equivalent to 



^ " The Temperature Coefficient of the Ferro-magnetic Metals." Nature, 

 Aug. 25th, 1910. "The Temperature Coefficients of the Ferro-magnetic 

 elements in corresponding states." Phil. Mag., Jan., 1912, p. 36. 



July 2nd, igi4. 



