356 



TT. NAGAOKA. 



torsion in these two cases is not strictly comparable, the strain caused 

 by twist or by twisting being somewhat different. 



The difference between the two will bè seem from the accompany- 

 ing; figure, in which the 



Fig. 



ioo c 



so c 



no c 



-in 



20 c 



10 



40 



ÔO 



abscissa gives the mag- 

 netizing force and the 

 ordinate represents the 

 twist or twisting corres- 

 ponding to the maximum 

 transient current. Curve 

 I. is for the method of 

 sodden twisting while II. 

 is for the method of re- 

 versal. 



If we compare Figs. 6 and 7, we notice that in the latter I. is 

 above II. while in the former II. is above I. This at first sight seems 

 paradoxical, but we see that one is a natural consequence of the other. 

 We saw that for the same angle of torsion, a greater magnetizing 

 force must be applied to make the current attain its maximum 

 strength by the method of reversal than by sudden twisting. Thus 

 it would follow that to make the current reach its maximum value in 

 a given magnetizing field by the former method the amount of twist 

 must be less than the corresponding angle given by the method of 

 sudden twisting. On this account II. lies below I. in Fig. 7. 



The strain at any point by twisting the wire depends on the 

 distance of the point from the axis of the wire. All parts of the 

 normal section which are at equal distances from the axis of the. wire 

 will he equally strained. Evidently the outer part of the wire must 

 suffer the greater strain. With the same angle of torsion, the 

 strain must be greater in the thick wire than in the thin. Had the 



