WIEDEMAXÎJ EFFECT IN FERROMAGNETIC SUBSTANCES. 



13 



Twist hij Tavijing the circular ßeld. Fig. 13 represents the result 

 for soft iron ; as thé circular field is increased, the twist is increased 

 first slowly and then rapidly. As the longitudinal field is increased, 

 the amount of twist reaches a maximum and then gradually dimini- 

 shes ; and if the field is strong enough, the twist occurs at first in 

 the opposite direction and then in the ordinary. Comparing the 

 above results with those obtained by varying the longitudinal field, 

 we notice one marked difterence that for the same circular and 

 longitudinal fields, the torsion is laig'ely dependent on the order in 

 which they are applied. The twist obtained by first applying the 

 circular field and then the lono-jtudinal is several times o^reater than 

 the twist obtained, when the order of npplying them is reversed. 



In nickel, the twist is opposite to that of iron ; under a given 

 longitudinal field, it increases nearly in a constant rate as the 

 longitudinal current is increased, as seen from Fig. 14. For a given 

 longitudinal current, the twist reaches a maximum and then gradually 

 diminishes as the longitudinal field is increased. Here again, we 

 also observe a dependence of the twist on the order of applying 

 longitudinal and circular fields. The twist obtained by the appli- 



