72 II. NAGAOKA AND K. HOXDA. 



loiigitiulinally mngiietized -wire and on ferromagnetic wire travers- 

 ed by an electric current. The strain caused hy twisting a 

 circular wire can be resolved in elongation and contraction in 

 directions perpendicular to each other and inclined to the axis 

 of the wire at 45°. Taking these two principal axes of the strain 

 for those of x and v, we have for the strain. 



~d^= ^"^"^ 



du 

 dx 



dv - 



-- — =—i(or, 

 dij 



where (>^ denotes the amount of torsion and r the distance from 

 the axis. Resolving the magnetizing force which is in the direc- 

 tion of the axis of the cylinder, along the axis of elongation and 

 of contraction, we find that the circular magnetization which will 

 be called into play is equal to —\cürl:"H at a distance r from 

 the axis, the mean circular magnetization being -(oVHB, where 

 R is the radius of the wire. 



The transient current which will be thus induced in the w^ire 

 by suddenly twisting it is proportional to —l"H. 



Next suppose that the wire is traversed by an electric current 

 of intensitv G. Then the circular maofnetizino; force at a distance 

 r from the axis is 



By fipplying similar reasoning, we find that the mean longitudi- 

 nal magnetization is equal to - wl" C . We therefore conclude 

 that twisting the \Yire carrying the electric current gives rise to 

 longitudinal magnetization proj)orlional to —l-"C. Thus the 

 circular magnetization produced by tw^isting a longitudinally 



