2 AKT. 8.— H. XAItAOKA AND FC. HoXDA: 



§ 7. Wiedeiuanu effect in nickel steels. 

 § 8. Summary of the results. 



§ 1 Introduction. 



In the course of our researches on magnétostriction' Njf différent 

 ferromagnetic hodies, questions of various character presented them- 

 selves, both witli regard to the method of measurement and the 

 nature of the sample. The minuteness of the effect called forth pre- 

 cautions against diverse sources of error, such as the non-h(jmogeneity 

 of the magnetic field, and the mechanical force arising therefrom, 

 the non-uniformity of temperature, a slight disturbance of which Avas 

 in most cases sufficient to mask the strain, which we were seeking 

 after. All those different sources of error, however intricate they may 

 at first appear, can, by properly arranging the measuring appai-atus, 

 be eliminated. The method of observins: the chancre of length and of 

 volume, which we have already described in our former papers, and 

 the agreement of the results obtained in different experiments witli the 

 same sample will Ije a sufficient warrant for the soundness of the 

 apparatus and the method ( )f measurement. 



Apart from such instrumentalities, the diversity in the character 

 of magnetostriction wit li different samples is hardly to be avoided. 

 Experiments by Uhoads"-'^ with rolled or stretched sheets of ir<^n 

 sufficiently prove how the treatment of ferromagnetic bodies has great 

 influence on the change of length accompan\'ing the magnetization. 

 In our farmer experiment on the magnetostriction of iron, steel, and 

 nickel, the soft iron was what niay be practically considered homo- 

 geneous, lujf the nickel ovoid was turned into shape from a thick ])late. 

 It thus seemed advisable to repeat the experiments with more homo- 



1) Xagaoka and Honda, Journ. Sc. Coll. 9. 253, 189S ; 13, r.7, 1900 ; 13, 2r,3, 1900. 



2) Rhoads, Phys. Rev. 7, Ö5, 1898 ; Phil. Mag. Nov., 1901. 



