TOUSION AND MAGNETIZATION. 277 



values of h", calculated from the changes of volume and of 

 length in iron and nickel ovoids. Graphically represented (Fig. 

 6.), the fields of maximum twist by calculation coincide nearly 

 with that given by experiments, and the reversal of twist in iron 

 takes place in low^ fields as actually found by observation. The 

 quantitative differences are, however, tolerably large in iron, 

 but in nickel the amount of twist is nearly coincident with the 

 experimental values. Calculating, in the same manner, the 

 quantity of the transient current produced by twisting longitudi- 

 nally magnetized wires, we find a close coincidence between the 

 experimental and theoretical values in nickel, but the difference 

 is tolerably large in iron. In using the strain coefficients, we 

 must always bear in mind that these values are widely different 

 according to the nature of the specimen ; especially with wires, 

 we are not sure of its being magnetically isotropic. The apparent 

 discrepancy would probably be lessened, if we could measure the 

 twist as well as the strain coefficients on the same sj^ecimen. 

 The remarkable qualitative coincidence as regards the existence 

 of maximum twist and its reversal in iron are convincing proofs 

 that the theory, so far as wo know at present, admits of con- 

 necting various experimental facts in a common bond. 



As regards the mutual relations among the three different 

 phenomena above enumerated, it will suffice to state that several 

 of them have already been noticed by G. Wiedemann in his 

 researches on the relation between torsion and mairnetism. He 

 especially studied the relation between permanent torsion and the 

 effect of magnetizing the twisted wire. The principal object of 

 his researches was to expose the different aspects of the phenomena 

 involved in the relation between torsion and magnetization in order 

 to bring to light his ingenious theory of rotatory molecules. 



