MAGNETIZATION AND MAGNETIC CHANGE OF LENGTH. 45 



The magnetization of annealed cobalt at high temperatures 

 was first observed by Professor Nagaoka and Mr. Kusa.kabe'^. 

 The present results generally agree with those obtained by them, 

 but in our case, the cooling in liquid air slightly altered the 

 the magnetic property. In Fig. G b, the point corresponding to 

 the magnetization in liquid air is also included. 



As the temperature rises from — 186°C, the magnetization in 

 a constant field increases at first slowly and then rapidly, till 

 it reaches a maximum at about 300°C, after which it decreases. 

 The magnetization reaches a small minimum, and theii begins to 

 increase, and after passing through another maximum, rapidly 

 decreases, reaching its critical point at 1090°C for H = 400. The 

 descending branch of the curves cuts the ascending branch at 

 about 850°C from downward to upward ; but its general course 

 is similar to that of the ascending curve. The minimum point in 

 the ascending branch is about 4o0°C, and nearly coincides with 

 the singular temperature observed by us in the change of length 

 by magnetizationf ; at this temperature the sign of the length 

 change is reversed for all fields. 



It is also to be noticed that the course of the curve beyond 

 the critical point is nearly parallel to the axis of temperature. 



Nickel. The specimen, which was first cooled in liquid air, 

 was heated and the magnetizations at ten different ascending 

 temperatures were observed ; since the dynamo stopped, when the 

 temperature attained 1150°C, the magnetizations at decreasing 

 temperatures were not taken as in tlie other cases, excej^t for the 

 maximum field only. 



The curves of the magnetization to the temperature are 



■•^■) Nagaoka and Kusakabk, loc. cit. 



t) Honda and Shimizu, Jour. Coll. Sei., XIX, Art. 10, 1903; Phil. Mag. VI, p. 392, 1903. 



