CHANGE OF DIMENSIONS BY MAGNETIZATION. 83 



the observation was finished, the key was reversed, so that the 

 circular magnetizing current was then called into play. During 

 this process, no gradual displacement was observed, showing that 

 the temperature of the tube remained unclianoed durinsr the re- 

 versai, but at the same time an instantaneous deflection was 

 noticed, which showed the change of length by circular mag- 

 netization. By reading the displaced position of the line in the 

 micrometer ocular, tlie deflection corresponding to the longitudinal 

 magnetization was noted. The tube was then demagnetized as 

 regards the longitudinal magnetization, the circular magnetization 

 remaining constant. The same process was repeated for stronger 

 fields, till a set of observations w^as completed. 



7. How the rise of temperature afiects the change of length 

 by magnetization will be seen from Fig. 2. The change of 

 length at ordinary temperature is somewhat less than that w^hich 

 Prof. Xagaoka and myself^' have obtained for an ovoid made of 

 the same specimen. The diiference may perhaps be explained 

 by that of annealing and of the geometrical shape of these 

 samples. The temj^erature was measured by inserting a mercury 

 thermometer inside the tube. Its effect is thus tolerably large ; 

 the rise of temperature is attended with an increase of the 

 change of length in weak fields, and is accompanied with a 

 decrease in strong fields. From the same figure, w^e obtain the 

 relation of temj^erature to the change of length at a constant 

 field as shown in Fig. 3. It is well know^n that the magnetization 

 of nickel increases with temperature in low fields and decreases 

 in strong ones ; but under the temperature of 100° C, the change 

 of masjnetization is too small to account for the chan^-e of lenofth. 



1) Nagaoka and Honda, Preceding paper. 



