416 Dr. J. R. Ashworth on the Theory of 



the paramagnetic equation, which applies above the critical 

 temperature. 



It remains to show that the abnormal changes of specific 

 heat and of electric resistivity with temperature, which are 

 characteristics of the £erro-magnetic metals, are to be 

 expected if this view of the intrinsic field is adopted. 



8. Specific Heat. — Since the magnetic molecules are almost 

 entirely free from rotational constraints except for a small 

 magnetic intrinsic field, whilst the constraints under which 

 thermal agitation takes place due to the large molecular field 

 are very great, the energy at ordinary temperatures is almost 

 entirely concentrated in the three degrees of freedom 

 associated with trans iatory movements; but as the temperature 

 rises, the molecular field becomes weaker, and, when the 

 critical temperature is approached, the energy becomes 

 mainly kinetic, and, in virtue of the magnetic forces, it is 

 shared with the additional two degrees of freedom associated 

 with magnetic vibrations and rotations. The specific heat thus 

 increases up to the critical temperature. But just above the 

 critical temperature, experiments show that there is a sudden 

 drop in the specific heat to lower values. This is accounted 

 for by the fact that just at or above the critical temperature, 

 when rotations of the molecules are becoming established, the 

 mutual magnetic forces become very small, and the energy 

 of thermal translatory movements is not as freely commu- 

 nicated to and shared with rotational movements; thermal 

 agitation for higher temperatures will again be mainly 

 confined to translations and the specific heat will fall to a 

 lower value. 



The experiments of Pionchon * and of Weiss & Beck t 

 on the change of specific heat with, rise of temperature in 

 ferro-magnetic substances are of great interest in this 

 connexion, and show how far these views are supported by 

 facts. 



The following table of specific heats is constructed from 

 their observations : — 



At At Orit. 



17° C. Temp. Ratio. Rise. Fall. Ratio. 



Magnetite 0-165 0275 3/5 0*110 0-055 2/1 



Nickel 0-098 0-153 3/47 0"055 0-027 2/1 



Iron 0-101 0-314 3/9-3 0-213 0-112? 2/1 



Cobalt 0-108 0-192? 3/5 "4 ? 0-084? — — 



* Pionchon, Ann. Chim. Phys. 6 ser. xi. p. 23. 

 t Weiss & Beck, J. de Phys. ser. 4, vii. p. 249. 



