EFFECT OF TWIST ON THE MAGNETIZATION OF NICKEL AND IKON. 203 



there is the same curious reversal in the hysteresis. 



Repetition of Thomson s experiments. — I shall first of all describe 

 some of the curves obtained for small amounts of twist, being merely 

 a repetition of Thomson's experiments. An iron wire 0.G6 mm. thick 

 and 40 cms. long was well annealed by means of a spirit lamp, and 

 arranged in the same way as the nickel wires had been. The wire 

 was then twisted through 180° in both directions, the strength of the 

 magnetizing field being kept constant. The curves thus obtained 

 during cyclic changes of torsion are shown in Figs. 30 and 31. The 

 former was obtained under weak longitudinal stress in the magnetizing 

 field J § — 2.9. The latter is plotted from observations made in the 

 same field, the longitudinal stress amounting to 1800 kgrms. per sq. 

 cm. 



The effect thus produced by twisting iron is not so complex as 

 for nickel, and the change in magnetization is but a small fraction of 

 the whole. The curves obtained under various loads are nearly all 

 similar in shape, and for the most part agree with those given by 

 Thomson. 



New experiments were made by using a wire of the same length 

 taken from the same specimen, and twisting it through ± 360° (±9° 

 per cm.). The curves thus obtained in different magnetizing fields 

 are plotted in Tigs. 32, 33, 34. The hysteresis in these magnetiza- 

 tion curves is such that in the returning branch the curve is lower 

 than in the going branch. The comparison of curves subjected to 

 twists of ± 4°.o and ± 9° will shew that everything remains the same 

 except in a single point. As the twist is increased, the ascending 

 and the descending branches of the curve tend gradually to approach 

 towards each other, although the hysteresis has the same sign in both 

 cases. Thus the amount of hysteresis in iron is affected by different 

 twists, while the increase of the magnetizing force seems to cause no 



