by twisting Magnetized Iron and Nickel Wires. 131 



Nickel Wire (r=043 millim., Z = 29*4 centirn., § = 27*5). 



T. 



Reading of 



ballistic 



galvanometer. 



T. 



Reading of 



ballistic 



galvanometer. 



o 



10 



13 



O 



50 



74 



15 



21 



60 



77 



20 



35 



70 



79 



25 



46 



80 



79-5 



30 



57 



90 



80-3 



40 



69 



100 



80-5 



If the maximum exists, it must 



The result is plotted in fig. 4 by dotted lines, where the 

 ordinates are measured upwards for convenience, although 

 they are actually below, as in fig. 1. The general feature of 

 the curve does not differ much from those obtained for iron 

 wires. The increase of the current beyond the "Wendepunkt " 

 takes place very slowly, but it does not reach a maximum 

 even for the twist of 100°. 

 be for a larger angle of twist 



It has been remarked by Professor Ewing that the produc- 

 tion of the transient current is a natural consequence of Sir 

 William Thomson's * discovery, that seolotropic stress gives 

 rise to an seolotropic magnetic susceptibility in iron. By 

 twisting the wire, the lines of induction, originally parallel to 

 the axis, are changed into helices. The component in the 

 plane section, normal to the axis of wire, induces the transient 

 current above described. Taking the Villari reversal into 

 consideration, he also explained why the transient current in 

 iron does not flow in the opposite direction, when the mag- 

 netizing force is greatly increased. 



The development of seolotropic susceptibility by twisting 

 the nickel wire, will similarly explain the production of 

 transient current in that metal. The stress on twisting the 

 wire is equivalent to extension and compression along lines 

 perpendicular to the radius, and inclined at 45° to the normal 

 plane section. According to the experiments of Sir William 

 Thomson f and Professor Ewing J, the susceptibility in iron 



* Phil. Trans. 1878 ; or ' Mathematical and Physical Papers,' vol. ii. 



t L.c. 



X Phil. Trans. 1888. 



