ox MAGNETOSTRICTION. 



11 



In low fields, the leDgth increases and at last reaches a maximum, 

 whence it gradually diminishes, till it indicates no elongation. The 

 decrease goes on steadily, but the rate of change becomes gradually 

 less, and at last assumes an asymptotic value. As will be seen from 

 the graphical representation (Fig. 2), the general feature of the curve 

 representing the length change resembles that for iron, with slight 

 difference in quantitative details. 



{h) Xickel (Fig. 2, PI. I.). 



The nickel ovoid, which we have formerly used for the measure- 

 ment of length and volume changes, was prepared from a thick plate 

 of the same metal. Although the ovoid was annealed in charcoal fire 

 for several days, lack of homogeneity was undeniable. To guard against 

 such mischances, we have tested a new specimen, supplied by Johnson 

 and Matthey, turned in the form of ovoid from a cylindrical rod. 



The nature of the change does not materially vary from the 



