MAGNETISM AND TWIST IN IRON AND NICKEL. 535 



polarity which is produced when the wire conveying the current is twisted. Notwith- 

 standing this fundamental contrast, however, there is great similarity between the two 

 metals in other respects. The phenomenon of the magnetic " lagging and priming " 

 exists in both ; and the effect of tapping is, broadly speaking, the same. 



A striking feature is the reversal with the current of the polarity acquired by the 

 twisting. This polarity is powerfully residual, and has, especially in the case of nickel, 

 a remarkably high value. Such phenomena point to a very complex molecular structure ; 

 and none of the ordinary simple theories of molecular magnetism can satisfactorily 

 explain these various effects. Not until we have some clearer conception as to the 

 properties of groups of magnetic molecules can we hope for anything like a co-ordination 

 of the complex relations of twist and magnetism. These relations, however, worked out 

 experimentally, may lead us finally to this very conception which we at present lack. 



One thing, however, is clear. The first effect of a shearing stress upon the molecular 

 groupings is not only to increase the average intensity in the direction of the magnetising 

 force, but also to bring into prominence a relatively high intensity in directions at right 

 angles thereto. For longitudinal magnetising forces this truth is established by experi- 

 ments on the transient current, as carried out by Mr Nagaoka, and more recently by 

 Dr Zehnder (Wied. Ann., 1890). Mr Nagaoka has shown that the reversal of the 

 magnetising force after the wire has been twisted produces a transient current of the 

 same order of intensity as the transient current produced by twisting the magnetised 

 wire. This is essentially the same magnetic phenomenon as the reversal of polarity when 

 the current is reversed along a twisted wire, so that the remark made a few sentences 

 back is a perfectly general one. 



