f)56 Messrs. K. Honda and S. Shimizu on the 



reverse. Taking into account the demagnetizing force, the 

 discrepancies with regard to the field of the maximum twist 

 and the slow diminution can easily be reconciled. 



The direction of twist in cobalt is the same as in nickel. 

 In cast cobalt the amount of twist is rather large, as shown 

 in fig. 1 1 . The twist increases at first slowly and then rapidly, 

 till it reaches a maximum : it then gradually decreases, and 

 ultimately changes its direction as the field is increased. 

 Thus the 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 

 twist after reaching the maximum is very slow and its direc- 

 tion does not change, though the field is pushed to 1200 c.G.s. 

 units. The results for annealed as well as for cast cobalt are 

 just what is to be expected from the magnetostriction of these 

 specimens. It is also to be observed that these cobalt bars 

 were made of different samples. 



Twist by varying the circular field. — Fig. 13 represents the 

 results for soft iron ; as the circular field is increased, the 

 twist is increased first slowly and then rapidly. As the 

 longitudinal field is increased the twist reaches a maximum 

 and then gradually diminishes ; if the field is strong enough 

 the twist occurs at first in the opposite direction and then in 

 the ordinary. Comparing the above result with those ob- 

 tained by varying the longitudinal fields we notice one marked 

 difference, that for the same circular and longitudinal fields 

 the amount of twist is largely dependent on the order in 

 which they are applied. The twist obtained by first applying 

 the circular field and then the longitudinal is several times 

 greater than the twist obtained when the order of applying 

 them is reversed. 



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

 o-iven longitudinal field it increases nearly at 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 decreases as the longitudinal field is in- 

 creased. Here again we observe that the twist obtained b}- 

 the application of the circular field, followed by that of the 

 longitudinal one, is far greater than the twist obtained when 

 the order of application is reversed. 



