58 Prof. Nagaoka and K. Honda on Magnetostriction 



inflexional points. These points do not appear in such a 

 remarkable degree as in steel, but their whereabouts can be 

 ascertained at a glance. 



(c) Cobalt (fig. 8). 



Just as we have noticed a difference in the length-change 

 and the intensity of magnetization in the cast and annealed 

 metals, we notice a difference in the volume-ohange for these 

 two bodies. The results of observation are plotted in curves 

 (fig. 8) . The behaviour of cobalt is unlike other ferromag- 

 netic substances — instead of showing increase the magnetiza- 

 tion causes diminution of volume, which in the annealed state 

 bears close resemblance to the character possessed by nickel, 

 indicating glimpses of two inflexion-points in the curve of 

 volume-change. With the cast specimen the feature is still 

 more different from the other ferromagnetic substances. ■ The 

 diminution of volume takes place quite rapidly in weak fields, 

 so that the curve soon reaches an inflexion-point. The rate 

 of diminution after passing this point is very small, the curve 

 passing on almost parallel to the axis of the field. This state 

 continues for a large range of fields, but the curve, instead 

 of showing another inflexion-point, reaches a point of maxi- 

 mum diminution of volume. The course of the curve turns 

 and proceeds in the same direction so far as the present eK- 

 periment goes. This character is possessed by cast cobalt 

 only among the numerous specimens of ferromagnetic sub- 

 stances hitherto experimented upon. Further, we may notice 

 that the amount of the change is, to a certain extent, greater 

 in cobalt than in iron, steel, or nickel. 



(d) Mckel-Steel (fig. i)). 



The volume-change in nickel-steel is simple but extremely 



Fig. 9. 



200 400 600 800 1000 1200 1400 1600 2000 



large compared to other ferromagnetic substances. The 

 common feature of the change, as will b£ seen from the 



