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XII. Magnetic Qualities of Nickel (Supplementary Paper). 

 By J. A. EWTNG, F.R.S., Professor of Engineering in University College, Dundee. 



Received Juno 14, Read Jane 21, 1888. 



[PLATE 17.] 



THE present paper is a supplement to one with the same title, by the author and Mr. 

 G. C. COWAN, which was read before the Koyal Society on May 17 (p. 325, supra). 

 In that paper experiments were described in which the effects of stress, consisting of 

 longitudinal pull, on the magnetic permeability and retentiveness of nickel had been 

 examined, and it was shown that longitudinal pull had an immense influence in 

 reducing both induced and residual magnetism in nickel. It was, therefore, to be 

 expected (as Sir WILLIAM THOMSON pointed out in his first discussion of the effects 

 of stress on magnetic quality*) that longitudinal compression would make nickel more 

 susceptible of magnetisation, and more ready to retain magnetic polarity. Experi- 

 ments on the magnetisation of nickel under compression have now been carried out 

 under the author's directions by two of his students, Mr. W. Low and Mr. D. Low, 

 and the results are described below. Further experiments have also been made to 

 investigate the magnetisation of nickel, in very strong magnetic' fields, by the method 

 already used for iron by the author and Mr. W. Low,t and the results of these are 

 given at the end of this paper. 



In dealing with the effects of tensile stress on magnetic quality, it is convenient to 

 test the metal in the form of a long wire, long enough to prevent the ends from 

 materially affecting the magnetic field throughout the main part of the length. But 

 in dealing with stress of compression this method of approximating to the condition 

 of endlessness is impracticable. Dr. HOPKINSON has shown that a short bar may be 

 brought to a condition of endlessness, suitable for the measurement of its magnetic 

 susceptibility, by sinking its ends in a massive yoke of iron, which affords an easy 

 path for the return of the lines of induction from end to end, outside the bar, and he 

 has made use of this plan in determining the form of magnetisation curves for various 

 samples of iron and steel.J This method lends itself well to experiments on the 



* ' Phil. Trans.,' 1878, or ' Reprint of Papers,' vol. 2, p. 368. 



t " On the Magnetisation of Iron in Strong Fields" (1), 'Roy. Soc. Proc.,' vol. 42, p. 200; (2) 'Brit. 

 Assoc. Report,' 1887, p. 586. 



J Hoi'KiNSO.N, " Magnetisation of Iron," ' Phil. Trans.,' 1885, p. 455. In Dr. HOPKINSON'S experiments 



30.10.b8 



