Length in Iron, Steel, and Nickel Ovoids by Magnetization. 341 

 the axis. Thus 



81, = 0. 



Consequently the circular magnetization which will be 

 called into play is equal to — j;cor.k"K at distance?' from 

 the axis, the mean circular magnetization being — ©RA/'H, 

 where R denotes the radius of the wire. The transient current 

 which will be induced in the wire by suddenly twisting it, is 

 proportional to k"H. 



Next suppose that the wire is traversed by an electric 

 current of intensity C ; then the circular magnetizing force at 

 distance r from the axis is 



20 



By applying similar reasoning, we find that the mean longi- 

 tudinal magnetization is equal to — wk"Q. We therefore 



conclude that twisting the circularly magnetized wire gives 



... 

 rise to longitudinal magnetization proportional to k f 'C Thus 



the circular magnetization produced by twisting a longi- 

 tudinally magnetized wire has reciprocal relation to the 

 longitudinal magnetization caused by twisting a circularly 

 magnetized wire *. 



The view put forward by Prof. Ewing f for explaining the 

 existence of the transient current by means of seolotropic sus- 

 ceptibility is similar to what would follow from KirchhofTs 

 theory, but it fails to give the amount of the current or the 

 magnetization which would be produced by twisting. 



The theoretical inferences which we can draw at a glance 

 from the curves of k f/ H (fig. 3, dotted line) are as follows : — 



1. The transient current as well as the longitudinal mag- 

 netization produced by twisting an iron or steel wire is opposite 

 to that of nickel up to moderate fields. 



2. The transient current as well as longitudinal magneti- 

 zation produced by twisting an iron, steel, or nickel wire 

 reaches a maximum in low fields. 



3. In strong fields the direction of the current as well as 



* Voigt, Compendium der theoretischen Physik, Bd. ii. p. 203 (1896) : 

 Drude, Wied. Ann. Bd. lxiii. p. 8 (1897). 

 t Ewing, Proc. Rov. Soc. vol. xxxvi. (1884). 



