64 H. NAGAOKA AND K. HONDA. 



were prepared from a thick plate, and were nearly pure nickel, the 

 quantity of iron present as an impurity being inmeasurably 

 small. As the material is likely to become homogeneous by 

 repeated annealing, the ovoids were carefully annealed for 

 about 50 hours. The ovoid was wrapped in asbestus and 

 placed in a thick metal tube, the interspace between the ovoid 

 and the wall of the tube being filled with fine charcoal powder. 

 The tube was then placed in charcoal fire. When the ovoid was 

 annealed in this way, there were some traces of surface oxidation. 

 The change of volume after each annealing was examined with 

 the result that it became evident that the process of annealing 

 increases the etfect. It therefore appears that the previous history 

 of the specimen exercises an important effect on the magnetization 

 and on the dimensions of ferromagnetics as affected by magneti- 

 zation. The anomaly in the length change noticed by Bidwell 

 in two specimens of nickel wire is probably not the effect of 

 temperature, but is perhaps to be ascribed to the cause above 

 stated. In contradiction to our former result with a square 

 prism, the ovoid showed increase of volume. The amount of in- 

 crease was small compared with the decrease noticed in the 

 previous experiment. Cantone^^ obtained a tolerably large increase 

 of volume in nickel ovoids ; our former result was nearly half as 

 large, while in the present experiment, there is a slight increase. 

 The discrepancy is probably due to the difference of treatment 

 before the specimen can be converted into a proper shape for 

 experimenting, and also to its chemical composition. 



11. The volume change of ferromagnetics considered as a 

 function of the magnetizing field takes place very slowly in weak 

 fields ; it then increases in a more rapid ratio till it reaches the 



1) Cantone, Atti della K. Accad. die Lincei, 6, (1), 257, 1891. 



