of Steel, Nickel, Cobalt, and Michel- Steels. 67 



in field »£), and that the mean longitudinal magnetization caused 

 by twisting a ferromagnetic wire carrying an electric current 

 C amounts to 



-i<ok"C ..(B) 



The reciprocal relation between these two phenomena is thus 

 apparent at a glance. We shall next show how the same 

 phenomena are reciprocally related with torsion produced 

 by the interaction of the longitudinal and circular magneti- 

 zations. 



The stress-components in a magnetic medium as given by 

 Kirchhoff are as follows : — 



z - x <=-(i + *4v 



Taking the axis of z in the axial line of the wire, and two 

 other axes in the plane perpendicular to it, we see that the 

 component magnetic forces in a longitudinally magnetized 

 wire traversed by an electric current are 



a= — 7isin0, /3 = hcos0, y = ^>> 



where h denotes circular field given by 



. 2Cr 



C being the current, r the distance of the point from the 

 axis of the wire, R the radius, and 6 the angle between r and 

 the axis of x. 



The stress-components in a ferromagnetic medium acted 



F 2 



