ON MAGNETOSTEICTIOX. 



25 



Cobalt. (Fig. 7.) 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 chansfe for 

 these two bodies. 



The behaviour of cobalt is unlike other ferromagnetic sub- 

 stances; instead of showing increase, the magnetization causes dimi- 

 nution of volume, which in the annealed state bears close resemblance 

 to the character possessed by nickel, indicating glimpse of two in- 

 flexion points in the curve of volume change. With the cast speci- 

 men, this feature is still more different from the other ferromao-netic 

 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 pre- 

 vails in a large range of fields, but the curve, in place of showing 

 another inflexion point, reaches a point of maximum diminution 



