TORSION AND MAGNETIZATION. 267 



Twist by varying the cii^cular field (Fig. 2). — Here we 

 notice a slight dissimilarity between iron and nickel. In 

 iron, the twist increases with the strength of the circular field, 

 if the longitudinal field remains constant. Such is also the 

 case with nickel in moderate and strons; fields. In low lonsi- 

 tudinal fields, however, the twist does not continue to increase with 

 the circular, but we notice a maximum as will be clear in the 

 figure.- There is great experimental difficulty in increasing the 

 circular field, inasmuch as the heating of the wire becomes very 

 great and tlius materially deteriorates the result. 



The hysteresis accompanying the cyclical change of the cir- 

 cular magnetization deserves special notice (see Fig. 3). If the 

 longitudinal field besuch that with the increase of the circularly 

 magnetizing force, the twist reaches a maximum, the curve of twist 

 goes below the former course on weakening the circular magneti- 

 zation. The twist, however, goes on slowly increasing, till it 

 crosses the o??,-curve and then reaches a maximum, wlience it 

 gradually diminishes and ultimately vanishes in 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 thus for obtained are in accordance with the 

 experiments of Wiedemann and Knott ; we have only to notice 

 the discrepancy as regards the position of maximum tw^ist in 

 nickel. In Dr. Knott's experiment, the said point occurs in 

 tolerably high field, while in the present experiment, it occurs 

 nearly in the same field as in iron. It may partly be due to the 



