64 Prof. Nagaoka and K. Honda on Magnetostriction 



The hysteresis accompanying the cyclical change of the 

 circular magnetization deserves special notice. If the 

 longitudinal field be such that with the increase of the 

 circularly magnetizing force, the twist reaches a maximum, 

 the curve of twist goes below its former course on weakening 

 the circular magnetization. The twist, however, goes on 

 slowly increasing, till it crosses the ora-curve and then reaches 

 a maximum, whence it gradually diminishes and ultimately 

 vanishes in a negative field. The course after passing this 

 point is exactly the reverse of that already described. The 

 character of twist is exactly the same for iron as for nickel, 

 when we take the opposite character of twist into account. 

 The nature of the hysteresis is nearly the same when the 

 longitudinal magnetizing field is made to vary while the 

 circular field remains constant. 



The results are in accordance with the experiments of 

 Wiedemann and Dr. Knott, with the discrepancy in the position 

 of maximum twist in nickel, which occurs in a tolerably 

 strong field according to Dr. Knott. 



(b) Circular magnetization produced by twisting a longi- 

 tudinally magnetized wire. 



By twisting a longitudinally magnetized wire, circular 

 magnetization is developed which is measured by the transient 

 current at the moment when the tw T ist is applied. One * of 

 us found that the current due to twisting was opposite in 

 direction in these two metals, and that it reached a maximum 

 in moderate fields. As the magnetizing current was not very 

 strong, no conclusive measurements were made as regards 

 the nature of the transient current in strong fields. Jn order 

 to clear this point and see if any intimate relation with the 

 Wiedemann effect could be traced, fresh experiments were 

 undertaken by the same method as before. We have to notice 

 that the ferromagnetic wire was so placed in the axial line of 

 the magnetizing coil that it lay in a nearly uniform field. 



The measurements of the transient current for iron and 

 nickel wires are shown graphically in fig. 14. The current 

 for constant amount of twist increases with the strength of 

 the longitudinal field ; it, however, soon reaches a maximum, 

 whence it gradually diminishes. in nickel the transient 

 current attains asymptotic values in strong fields without 

 changing its direction, while in iron it is reversed in a field 

 of about 200 C.G S, units, when the twist is small. The 

 increase after the reversal is not pronounced, but becomes 

 finally asymptotic. 



* Nagaoka, Phil. Mag. Feb,, 1889. 



