EFFECT OF TWIST ON THE MAGNETIZATION OF NICKEL AND IRON. 195 



takes place in different specimens of nickel, and also for different 

 amounts of twist. The curve representing the changes of magneti- 

 zation when the polarity suffers reversal is, as already noticed, single 

 looped, whereas we get double looped curves in cases where there is 

 no reversal of polarity, that is, in cases in which the longitudinal 

 stress is sufficiently weak. Hence in the present case we should ex- 

 pect that, bv gradually increasing the magnetizing force, until the 

 1-uigitudinal stress of 5 kgs. weight is insufficient to cause reversal 

 of polarity, we shall ha able to transform single looped into double 

 looped curves. Tlv experiment when male fulfilled the expecta- 

 tion, as may be seen from Fig. 7. Here the field is 5.0 units ; the 

 carve has ceased to dip balow the zero line so that the polarity is not 

 reversed. At the same time, the curve, though unsvmmetrical with 

 respect to the line of zero twisting, turns out to be double looped. 

 On further increasing the held the two loops become more and more 

 symmetrical (see Fig. 8). Thus the question as to whether a given 

 curve will be single looped or double looped seems to depend on the 

 , existence or non-existence of the phenomenon of the reversal of pola- 

 rity. What has been stated in my earlier paper with respect to the 

 form of the magnetization curve for the twist of ± 4°. 5 per cm. is 

 also applicable for that of ± 0°.86 per cm. There is, however, a 

 remarkable difference in the change of magnetization which may be 

 expressed by saying that there is reversal of hysteresis between these 

 two different twists. 



Reversal of hysteresis for the twists of ± l°.-j and ± 1°.S. — In the 

 next series of experiments, the twists were taken larger. A wire 

 40 cms. long and 1 mm. thick was set in various magnetizing fields, 

 and twisted through a total range of ± 60° or through a twist of 

 ± 1°.5 pea- cm. The only longitudinal stress acting was the weight 

 of the twisting rod and the brass wire attached to the end of the 



