Manchester Memoirs, Vol. Iviii. (1914), No. 11. 5 



Appendix. 



1. Van der Waals' equation in terms of pressure (/), 

 density {p), and absolute temperature (Z) may be written 



where - is put for Van der Waals' b. 



Po 



The analogous ferro-magnetic equation is 



(^+/(/))(i-i)=A-7: 



Here /(I) represents the intrinsic field. If R' is an 

 unique constant, both below and above the critical tempera- 

 ture, and equal to the reciprocal of Curie's constant, then 

 it may be shewn that the intrinsic field in iron is of the 

 order 10^ gausses. 



2. The magnetic work done in transferring an element 

 of volume {dv) of magnetic material from a place where 

 the intensity of magnetisation is zero to a place where it 

 becomes / is 



The corresponding electrical work is 



Edq 

 where E is the potential difference, and dq the quantity 

 of electricity transferred. 



Let z be the electrochemical equivalent and ^ the 



density of the magnetic substance, then 



z 

 dv = ~^dq. 



If the magnetisation arises from the intrinsic field 



(//i), then 



/ 



