CHANGE OF VOLUME AND OF LENGTH. 73 



magnetized wire has a reciprocal relation to the longitudinal 

 magnetization caused by twisting ;i circularly magnetized wire/* 



The view propounded by Prof. Ewing"^ to account for the 

 existence of transient current by means of frolotropic suscepti- 

 bility is similar to what would follow from KirchhofV's theory, 

 but it fails to give the amount of the current or of the magnetiza- 

 tion which would be produced by twisting. 



The theoretical inferences which we can draw at a glance 

 from the curves of — /." II (Fig. 3) are as follows : 



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



zation produced by twisting an iron or steel wire is 

 opposite to that produced by twisting one of nickel, up 

 to moderate fields. 



2. The transient current as well as the lon2;itudinal mao-neti- 



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 



the longitudinal magnetization is the same in iron, steel, 



and nickel. 

 It has been established bv G. Wiedemann'^ that the lona;!- 

 tudinal magnetization produced 1)y twisting an iron wire carry- 

 ing an electric current is opposite to that produced in a nickel 

 one. The opposite character of the transient current in these two 

 metals has also been observed by Zehnder*' and independently by 

 one of us"'. The existence of a maximum transient current in 



1) Voigt, Kompendium der ihenrethchen rinjsik, 2, 20o, 189(5, Leipzig ; Drude, Wieil. Ann. 

 63, J^•, 1897. 



2) Ewing, rroc. Eo:;.'_Soc. 36, 1884. 



3) AViedemann, Elect ricitüt, 3. 



4) Zelnider, Wied. Ann., 38, C8, 1889. 



5j Nagaolva, Phil. Mag. [5] 29, 123,1890; Juunial of tlie College of Science, TGkyG, 3, 

 335, 1890. 



