[ 131 ] 



VIII. Hysteresis attending the Change of Length by Mag- 

 netization in Nickel and Iron. By H. Nagaoka, Riga- 

 hishi *. 



[Plates I. & II.] 



SINCE Joule's discovery f that the length of iron is 

 changed by magnetization, the subject has been studied 

 by Mayer |, Barrett §, Bidwell ||, and Berget If. Bidwell 

 carried the investigation into very strong magnetizing fields, 

 and discovered several new facts concerning the changes of 

 length in ferromagnetic substances. So far, however, nothing 

 has been definitely established regarding the manner in which 

 these substances change length during cyclic changes of 

 magnetization. The object of the present investigation is to 

 ascertain if there is any hysteresis in the changes of length 

 during magnetic cycles, and at the same time to determine 

 its amount. 



Several fruitless attempts were made before I obtained 

 any definite result. The first method I had recourse to was 

 that of interference-fringes. A small brass plate was brazed 

 to the end of an iron wire, and a plane glass plate placed upon 

 it. Separated by a thin air-film was a plano-convex lens of 

 about 40 centim. focal length, with 23 fine dots on its plane 

 face. The lens rested on a tripod. These different pieces of 

 apparatus were detached from Fizeau's dilatometer. The 

 change of length was determined by observing the displace- 

 ment of the fringes produced by sodium-light. From the 

 position of the dots it was possible to determine a change 

 amounting almost to a hundredth part of a sodium wave- 

 length D. But as each observation of the fringes required a 

 few minutes, it was difficult to keep the temperature constant ; 

 and, moreover, owing to the uniformity of distribution of 

 the fringes, it was not always easy to count the number dis- 

 placed. Consequently it was necessary to devise a more 

 delicate method, and, if possible, some means of compensating 

 for temperature-effects. 



* Communicated by Prof. C. G. Knott, D.Sc, F.R.S.E. 

 t Reprint of Papers, vol. i. p. 235. 

 % Phil. Mag. [4] xlvi. p. 177. 

 § * Nature,' 1882. 



|| Proc. Roy. Soc. 1886 ; Phil. Trans. 1888 ; Proc. Roy. Soc. 1890. 

 % Compt. Rend, torn. cxv. p. 722. 



K2 



