330 



H. NAGAOKA. 



If after the magnetizing field has attained a certain value, it lie grad- 

 ually decreased, the wire again twists back. Tlie twisting produced hy 

 the removal of the magnetizing force is, however, far smaller than the 

 untwisting produced by the increase of tlie magnetizing force. Con- 

 sequently, the return curve goes above the other, as is shown hy the 

 dotted line in curve (1) Fig. I. This fact can be briefly expressed by 

 saying that there is magnetic after-effect in the twisting which becomes 

 conspicuous l)y the removal of the magnetizing force. So long as the 

 îimount of permanent twist remains very small, the curve showing the 

 torsional etfect of a continuously changing magnetie force reseml)les the 

 ordinary curve of magnetic hysteresis. 



The al)ove remark does riot hold wlieri the permanent twist 

 exceeds a certain limit. The decrease of twist with increase of mag- 

 netization soon reaches a maximum. After this, the wire begins to 

 twist in spite of the increase (^f magnetizing force. The amoimt oi' 

 twisting of course varies witli the ])ermanent set of the wire as well as 

 with the amount of pulling stress. The following tal)]e gives the 

 amount of chano'e of twist with the wire of 0.17 mm. radius. 



