RESEARCHES <>\ 31 AOXETosTKIO'i'Lo.Y 



875 



In nickel there is generally decrease of magnetization in the 

 stretched state, except in weak field, where a slight increase of 

 magnetization was observed. Corresponding to the critical field in 

 iron, for which the change of magnetization is a maximum, there exists 

 also a critical field in nickel for which the diminution of magnetization 

 is a maximum. Further, it will he seen from the figures that the 

 change of magnetization i.s not exactly proportional to the amount of 

 longitudinal stress. 



Denoting the longitudinal stress by P, the ratio Aij gradually 

 decreases with increased loading j in nickel the ratio -^-^ dimi- 

 nishes at a greater rate as the field is increased. The rate of 

 diminution seems apparently to be smaller in a rod with smaller 

 loading. 



It appears from Prof. Ewing's i; experiment that the increase of 



magnetization in iron in weak field becomes more pronounced with 

 greater loading, but the field at which the magnetization becomes 

 smaller than in the unloaded state recedes towards the weaker side. 

 Although Prof. Ewing did not observe these points in fields greater 

 than H=8 for 2 kg. loading, which is far greater than that in the 

 present experiment, the general feature of the curves of magnetization 

 shows that if the loading be greatly diminished, the above-mentioned 

 field will become correspondingly large. Thus the present investiga- 

 tion agrees in its general features with Prof. Ewing's experiments. 



In nickel, a .-light increase of magnetization in weak field was 

 observed with the stretched rod ; whether this has any connection 

 with the Villari effect observed by Heydweiller 2) is a question, which 

 without special examination can not be easily decided. 



1). Ewing, Ph I. Trans. 196 (2) 607, 1835. 

 2). Heydweilli r med. Ann. 52, tö2, 189<J 



