﻿of Ferro-magnetic Elements in Corresponding States. 45 



The differences which are given in the last column are so 

 small that the correspondence may be treated as nearly exact. 



Since the curve tracing the change of fractional density 

 of water as a function of the reduced temperature is the 

 same for other liquids in general, and is at the same time 

 approximately the curve of change of fractional intensity of 

 the ferromagnetic elements, it follows that the temperature 

 coefficient of density of liquids and of magnetic intensity of 

 the ferromagnetic elements in corresponding states are very 

 nearly of the same magnitude. 



7. Parallel with this result is the law of Curie that under 

 a constant force the intensity of ferromagnetics at tempe- 

 ratures above the critical point is inversely proportional 

 to the absolute temperature, and hence the temperature co- 

 efficient of intensity in the paramagnetic condition is the 

 same as the temperature coefficient of density of a gas. 



Thus the behaviour of the magnetic intensity of the ferro- 

 magnetic elements under variations of temperature bears a 

 very clo?e analogy to the behaviour of the density of a fluid 

 under similar treatment. 



8. A study of the passage of a fluid from the liquid to the 

 gaseous state has led to the hypothesis that the constituent 

 molecules mutually attract one another, but at the same time 

 their thermal agitation plays the part of a repulsive force. 

 ]n any given state there is equilibrium between these effects. 

 By analogy Curie * suggests that the magnetic transforma- 

 tion from ferro- to paramagnetism may be due to the 

 magnetic molecules passing from mutual attraction to a state 

 of independence. This independence may arise in part from 

 expansion, and in part from the enhanced energy of oscilla- 

 tion of bi-polar molecules. Any given magnetic state is 

 then a state of equilibrium. 



In a fluid the continuous change from one state to the 

 other can be expressed most simply by Van der TVaals's 

 equation which recognizes the fact that there is a limit to 

 the density of a liquid and that the molecules exert a 

 mutual attraction equivalent to a pressure. 



In magnetism it is generally agreed that there is a limit 

 to magnetic intensity, and that the magnetic molecules exert 

 a mutual attraction, and these are the counterparts of the 

 two salient facts in Van der Waals's equation. 



Thus the suggestive analogy between the gas laws and 

 the laws of paramagnetism, first pointed out by P. Curie, is 

 capable of extension and application to liquids and ferro- 

 magnetics, in so far as liquid density ami ferro-magnetic 

 intensity can be treated as functions of the temperature. 



* Loc, cit. 



