10 AKT. 14.— K. HONDA AND S. SHIMIZU : 



direction of ciirrcnts wa.s also .so chosen that the rotation of tlie mirror 

 causes contraction of tlie weak sjning stretching the thin copper wire. 

 Witli tlie present apparatus, the twist amounting only to 1.83" x 10"' 

 per cm. of our specimen was easily read. 



The measurement was conducted in the same order as in the 

 case of nickel steels. Here we noticed that a slight residual magne- 

 tism considerably aflected our results ; lience before each deflection 

 was taken, demagnetization was carefully effected. 



Twist hij vanjiH() tlii' loiujitiulinal field. Fig. 9 represents the 

 curves of twist per cm. in an iron bar plotted against the external 

 longitudinal field. Here C is the longitudinal current per square 

 centimeter. The o^eneral course of the curves is similar to that observed 

 in the wire of the same metal. Under a constant circular field, the 

 angle of twist increases at first sl<3wly and then rapidly, till it reaches a 

 maximum in a held of about 100 C.G.S. units ; it then diminishes and 

 ultimately changes its direction. The field in wliich the twi.st reaches 

 a maximum, and also the field of reversal are markedly larger in the 

 bar than in the wire. Moreover, the diminution of twist in the bar, 

 after reaching a maximum, is comparatively slow. 



The results for nickel are drawn in Fig. 10 ; the general features 

 <3f the curves are similar to those in the wive of the same metal. T'he 

 direction of twist is opposite to that in iron ; but the course of the 

 curves is similar to that in iron, the only difference being that even 

 in stronir fields, the direction of twist is not reversed. The field in 

 which tlie twist reaches a maximum is also considerably larger in the 

 bar than in tlie wire, and the diminution of twist, after reaching 

 a maximum, is comparatively slow. 



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. 11. 

 The twist increases at first slowly and then rapidly, till it reaches a 



