278 H. NAGAOKA AND K. HONDA : 



Elegant as it at first sight appears to be, Wiedemann's theory 

 abounds with hypotheses which we are not always warranted in 

 making. 



In his work on the applications of dynamics to physics and 

 chemistry, J. J. Thomson has propounded a new method of 

 investigating the mutual relations between the effects of various 

 physical agencies. He showed that the existence of a certain 

 phenomenon involves as a natural consequence that of another 

 reciprocating with it. As an application of his method, he showed 

 that if the wire be twisted by the interaction of longitudinal and 

 circular magnetizations, a transient current will be produced 

 simply by twisting a longitudinally magnetized wire and a 

 longitudinal magnetization will be developed by twisting a cir- 

 cularly magnetized wire. 



The peculiar feature of Kirchhoff's theory lies in the simple 

 and natural way of elucidating the relations between the various 

 kinds of strain caused by magnetization and the effects of stress 

 on magnetization. Just as we can study the various elastic be- 

 haviour of isotropic bodies by knowing the bulk- and stretch- 

 moduli, we have to deal, in Kirchhoff's theory, with the strain 

 coefficients k' and k" which play the rules of different moduli 

 in the theory of elasticity. 



The reciprocal relations between the strain caused by mag- 

 netization, and the effects of stress on magnetization, as found 

 by actual experiments, will be found to be of paramount im- 

 portance in arriving at a correct theory of magnetostriction. 

 The strain accompanying the magnetization of ferromagnetic metal 

 will be determined, when we know the effects of stress on mag- 

 netization and vice versa. As regards the relations between twist 



