ox TRANSIENT ELECTRIC CURRENTS. 377 



after passing the maximum dips very rapidly describing a curve 

 which is more curved than that for the unloaded wire. The current 

 decreases very rapidly, so that it is soon reduced to a very small 

 amount. Thus after the angle of torsion exceeds 90° or thereabouts, 

 the deflection of the galvanometer magnet produced by reversing the 

 direction of the magnetizing force is scarcely appreciable. On greatly 

 increasing the twist, the transient current remains in the same state, 

 so that it is quite probable that the current ultimately becomes 

 vanishingly small when the twist is very great, but the direction of 

 the current will never become reversed. Curves II. and Y. show these 

 features very distinctly. 



It must not be supposed that a similar curious change takes 

 place in the transient current whenever the wire is loaded. It is only 

 in weak magnetizing fields that the changes above described take 

 place. On examining the transient current in .$ = 10.6 with the thick 

 wire subjected to a longitudinal stress of 5 kg. weight, Curve III. was 

 obtained. The course of the curve is slightly different from that 

 obtained with the unloaded wire in § = 9.8 (see Curve I.). The 

 maximum point is present for nearly the same angle of twist, both 

 for the loaded and for the unloaded wire. The curve dips after 

 passing the maximum, but the course is nearly straight and not 

 curved as in II. and V*., so that the transient current will be appre- 

 ciable unless the twist becomes very great. 



According to the researches of Professor Ewing, longitudinal 

 stress always decreases the magnetic susceptibility of nickel, while 

 compression always increases it. If we resolve the torsional stress, 

 as has already been done into extension and compression at right 

 angles to the radius of the wire, and inclined at 45° to the plane section 

 normal to the axis, the circular component of the lines of induction 

 will be constantly on the increase as the twist is taken greater. If, 



