70 Prof. Nagaoka aW K. Honda on Magnetostriction 



]arge im 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 remarkable 

 qualitative coincidence as regards the existence of maximum 

 tw r ist and its reversal in iron are proofs that the theory, so 

 far as we know at present, admits of connecting various 

 experimental facts in a common bond. 



The reciprocal relations between the strain caused by 

 magnetization, and the effects of stress on magnetization, as 

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

 importance 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 magnetization and vice versa. As regards the relations 

 between twist and magnetization in iron and nickel, we may 

 conveniently place them under the following parallel 

 statements : — 



Strain produced bg magnetization. Effects of stress on magnetization. 



(1) A longitudinally (or circularly) (1') Twisting a longitudinally (or 

 magnetized wire is twisted by circularly) magnetized wire 

 circular (or longitudinal) mag- gives rise to circular (or longi- 

 netization. tudinal) magnetization. 



(2) Up to moderate fields, the twist (2') Up to moderate fields, the 

 produced by the longitudinal transient current (or the longi- 

 and circular magnetizations of tudinal magnetization) produced 

 an iron wire is opposite to that by twisting a longitudinally (or 

 in nickel. In strong fields, the circularly) magnetized wire, is 

 sense of twist is reversed in iron. opposite to that in nickel. In 

 The twist due to longitudinal strong fields, the direction of 

 magnetization of a circularly the transient current is reversed 

 magnetized iron or nickel wire in iron. The transient current 

 reaches a maximum in low fields. in iron or nickel wire reaches a 



maximum in low fields. 



§ 7. Summary. 



The results obtained in the present investigation can be 

 summarized in the following statements : — 



Magnetization. 



(1) The magnetization of cast cobalt is nearly double that 

 of the annealed metal. The magnetization of annealed cobalt 

 is characterized by its high differential susceptibility. 



(2.) The magnetization of 46 per cent, reversible nickel- 

 steel is between iron and cobalt (cast), while that of 3b' per 

 cent. Ni is nearly the same as in cobalt. The 29 per cent. Ni is 

 nearly half as magnetizable as nickel, and 2o per cent. Ni is 



