ON THE MAGNETIC QUALITIES OF NICKEL. 331 



loaded up to 12 kilogrammes and unloaded, repeatedly, while a strong field was 

 maintained in action. Fig. 6 shows the resulting changes of 3 first when the 

 magnetic field was 6'9, then 2T8, then 53'5, and lastly 116. The dotted lines in the 

 same figure show the changes caused by loading and unloading on the residual 

 magnetism that was left after the strongest field (116 c.g.s.) had ceased to act. 



The curves show that stress of pull, acting either on residual or on induced 

 magnetism in nickel, produces a large and continuous diminution of the magnetism, 

 and that cyclic variations of stress are attended by exceedingly little hysteresis in 

 the relation of magnetism to stress. The " off" curves lie distinctly below the " on " 

 curves, but only a little way below them. The hysteresis here is far less than in the 

 case of iron. 



The same piece of wire was next hardened somewhat by stretching it till the original 

 length of 26 '6 cms. was changed to a length of 27 cms., and the process of loading 

 and unloading was repeated, this time up to 18 kilos. The results are shown for two 

 magnetic fields in fig. 7. In the stronger field the " on" and " off" curves so nearly ^ 

 coincide that a single line only has been drawn. The piece of wire dealt with in this 

 experiment was the same, and in the same state, as the piece with which the cycle 

 shown by broken lines in fig. 2 was performed. 



Once more a set of curves of 3 aud $ were taken with this piece (hardened by 

 stretching), under loads ranging from to 18 kilos. These are given in fig. 8. They 

 show the same characteristics as those of earlier figures, with a still more striking 

 absence of susceptibility under the greater loads used here. With 18 kilos., for 

 instance, equivalent to about 50 kilos, per sq. mm., a force of 100 c.g.s. produced an 

 intensity of magnetisation amounting to barely 50. In the earlier curves of this 

 series the dotted lines show the magnetic changes that occurred as the magnetising 

 force was gradually withdrawn. 



Finally, the initial parts of the curves in this group were examined by repeating 

 the earliest portion of each magnetisation with the wire placed much nearer to the 

 magnetometer. This was to determine whether there is in nickel any crossing of the 

 curves similar to the crossing that occurs in iron, in consequence of the " Villari 

 reversal " of the effects of stress.* Nothing of the kind was discovered in this metal.t 

 The results of this experiment are given in fig. 9, and from them one may find the 

 initial magnetic susceptibility, or ratio of 3 to , at the very commencement of the 

 magnetising process. The first part of each curve is sensibly a straight line, until 

 reaches a value of about 5 c.g.s. units. In other words, for forces less than this the 

 susceptibility is as nearly as possible constant. When there was no load the initial 



Of. THOMSON, loc. eit.; EWINO, toe. cit. 



t October 4, 1888. It is, of course, possible that a crossing may take place at higher values of the 

 magnetic force than were reached in these experiments, bnt the analogy to iron points rather to a 

 crossing in the early portion of the curves, snch aa was looked for and not found in these experiments. 

 With regard to this point, see an experiment by THOMSON, ' Phil. Trans,' 1879, p. 83. 



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