ON MAGxMETOSTRIC'lTOX. 



13 



into ovoids of the same diuieosioiis as for the tw<3 former metals. 

 One of the ovoicls was examined in the state, in whicli it issued from 

 the latlie, while the other was annealed in charcoal fire for about 4 

 hours, after being carefully wrapped in asbestos paper. As the chano-e 

 of length by magnetization and the intensity of magnetization were 

 characterized by a remarkable difference in character, it would be 

 well to describe the phenomena separately for cobalt ovoids, which 

 underwent diff'erent treatments. 



Cast Cobalt. The behaviour of cast cobalt, as reg-ards the leno-th 

 change, is similar to that in nickel in weak fields. Instead of 

 reaching an asymptotic value as in nickel, the contraction of cobalt 

 reaches a maximum at about H=160, from which the metal gradually 

 recovers with increasing fields, till it attains its initial length in H=: 

 750. The metal however goes on elongating, but at a less rapid 

 rate, till i/=2000, which is the strongest field employed in the pre- 

 sent experiment. 



The table gives the observed changes ; representing the 

 change by means of a curve (Fig. 2), we notice a singular 



