60 Prof. Nagaoka and K. Honda on Magnetostriction 



as the enormous effect of magnetization on the bulk of the 

 alloy. In the present instance, we are at a loss to find which 

 of the two metals plays a predominating part in the magneto- 

 striction of nickel-steel ; perhaps a complete study- of the 

 subject from the lowest percentage to the pure nickel, and 

 the comparative investigation of the phenomena in the 

 succeeding stages, will reveal to us the groupings of the 

 constituent metals while entering into an alloy, and the part 

 played by them in the magnetization and the various 

 phenomena attending it. 



It may at first sight appear that the smallness of thermal 

 expansion in nickel-steel necessarily entails the minuteness of 

 the change of length and of volume by magnetization, but 

 no connexion seems to exist between the magnetostriction 

 and the deformation due to temperature variation, as illustrated 

 in the preceding experiments. 



§ 6. Wiedemann Effect in Iron, Nickel, and 

 Nickel-Steel Wires. 



(a) Twist produced by the interaction of circular and longi- 

 tudinal magnetizations. 



The subject was first studied by G. Wiedemann, who 

 established remarkable reciprocal relations with the longi- 

 tudinal magnetization produced by twisting a circularly 

 magnetized wire. Dr. Knott found that the direction of 

 twist in iron is opposite to that in nickel ; Bidwell afterwards 

 discovered that the twist in iron is reversed in high fields. 

 Unfortunately some of these experiments were undertaken 

 with wires w r hich were longer than that of the coil, so that 

 the magnetization was far from being uniform. 



The twist produced by longitudinal magnetization of a 

 circularly magnetized wire was measured in the following way 

 (fig. 10). To the extremities of a ferromagnetic wire (/) 

 21 cm. long were brazed stout brass wires (b, b), and a light 

 plane mirror (m) was attached to the lower one. The end of 

 the lower brass wire dipped in a mercury pool, while the 

 upper brass wire was clamped to a small tripod (t), which 

 rested on the top of a magnetizing coil, provided with hole-, 

 slot-, and plane-arrangement. One end of the accumulator 

 was connected with the tripod, while the other was led to a 

 mercury pool. The wire hung vertically in the axial line of 

 the coil, which was used for ail the preceding experiments. 

 The vertical component of the terrestrial magnetic held was 



