ON MAGNETOSTRICTION. 7 



The curves of niugiietization are represented in Fig. 1, PI. I. The 

 most magnetic of the ferromagnetic metals here examined is cast steel, 

 whose magnetization comes very near to that of soft iron. Of the 

 two kinds of cobalt, the cast specimen is nearly midway between steel 

 and nickel ; but with annealed specimen, the susceptibility is small in 

 weak fields, and less than in nickel, but tlie differential susceptibility 

 ( ^, j is greater in the strong, so that the intensity of magnetiza- 

 tion becomes ultimately greater than in nickel. 



Of the three kinds of reversible nickel steels, the 46% Ni speci- 

 men approaches steel, the 06% Ni lies near cast cobalt, and the 29% 

 Ni is less magnetic than pure nickel. The magnetization reaches 

 asymptotic value in fields less than those for steel or cobalt. The 

 25% specimen is only feebly magnetic, so that its magnetization is 

 scarcely to be detected by the magnetometer. There we notice the 

 singular fact, that the intensity of magnetization in nickel steel is 

 not proportional to that of the constituent metals. 



§ 3. Description of the Apparatus for Measuring 

 Changes in Length. 



The vertical and horizontal projections of the apparatus are 

 represented in Figs, a and h. The essential part consists of a stout 



Fig. a. 

 I, 



-4 



\ 



Fia:, h. 



brass bar 53 cm. long, 1 cm. broad, and 1.1 cm. high. It is ])rovided 

 with three levelling screws 1, L, I3. A carefully polished V-groove is 



