WIEDEMANN EFFECT IN FERROMAGNETIC SUBSTANCES. 



11 



maxiDiuin ; it then gradually decreases and ultimately changes its 

 direction as the field is increased. Thus, tlie course of the curves is 

 just the reverse of that in iron. 



The behaviour of annealed cobalt as regards the Wiedemann 

 effect is remarkably different from that of cast cobalt, as shown in 

 Fig. 12. In the first place, the amount of twist is much smaller in 

 the annealed than in the cast cobalt. Secondly, the field in which the 

 twist reaches its maximum is rather large in annealed cobalt. Thirdly, 

 the decrease of the twist after its maximum value is very slow and its 

 direction does not change, though the field is pushed to 1200 C.G.S. 

 units. These results for annealed as well as for cast cobalt are just 

 what is to be expected from the magnetostriction of these specimens. 

 It is als«) to be observed that these cobalt bars were made of different 

 samjjles. 



The following tables contain some observed angles of twist for 

 iron, nickel, and cobalt bars : — ■ 



Iron bar. 



