470 



liGiire the last term in the above expression becomes 



- (m . h). 

 Here h is the whole magnetic force acting on the particle, viz, 

 the Langevin force H (see below; with the exception of the molecular 

 tield kM. Omitting the constant term ^ Qg^"^ we tind 



p=-M{}\ — kM) = — Hi¥ + kM\ 



Collecting the different terms we obtain according to: 



Assumption A. 



1/ I y \ r \ \ \ 1 1 



2^37 3^372 '9 2 ^ 



If we write }1 = H -] — M -\- hj^ -\- kM for the total force which 



o 



is to be put into Langevin's formula, we can also write 



Assumption B : 

 U= 1 fn + ii/Y+ ^i/^iï + ^Al\ - H J/+ k3P + i Mhi^ 



1 



9 2 n r 



With the aid of the above expression for H we tind again 

 U=hHB—hnM -i- Ur 



We may combine the different terms of H — -H to one and write 

 it in the form k' M. There will be no objection to this, if we 

 consider that the term k M is by far preponderating. Then 



With this we find 



U={ H^ — {Jc M'' + U... 



The work done on the body at an infinitely small change is 



HdB 

 The heat to be supplied is then 



dQ=zdU—HdB. 



This gives 



dQ = H dH — k'M dM + dUr - H dB 

 = — HdM — k'MdM + dUr 

 = dUr — B. dM, 

 which relation agrees with equation (18) ofthe preceding communication. 



