446 THE ELECTROMAGNETIC FIELD. [PT. III. CH. XI. 



But since //, = 1 we have 



and accordingly the components of the vector potential may be 

 taken as 



(5) 



Every element of volume produces at x, y, z a portion of vector 

 potential equal to 1/r 2 times the vector product of its magnetiza- 

 tion by its vector distance from the point #, y, z. The mutual 

 energy of currents and magnets is then obtained by the equation 

 226 (5), omitting the factor ^. This method of treatment is 

 that of Maxwell*. 



From the above form for the vector potentials we may easily 

 express the solenoidal vector F, G, H as itself the curl of another 

 vector potential. For again replacing derivatives of 1/r by a, 6, c by 

 derivatives by x, y, z, 



(6) .J- 



so that if we introduce the vector potential of magnetization, with 

 components 



(7) 



* Treatise, Vol. n., Art. 405. 



