ON TRANSIENT ELECTRIC CURRENTS. 367 



smallness of the current in steel indicates that the stress produced by 

 twist has a smaller effect in steel than in iron. The principal point 

 of difference in these two substances is at the same time attended with 

 ;i difference in the permanent set acquired by the twisted wires. 

 These facts suggest that there exist certain intimate relations between 

 the transient current and the limit of elasticity. 



Transient Current in Nickel. 



As I have already remarked, the present investigation originated 

 in searching if the transient current does not show any peculiarity 

 in the magnetized nickel wire, which has undergone the reversal of 

 polarity by the combined action of torsion and longitudinal stress. 

 With this object in view, the transient current produced by twisting 

 the nickel wire was examined under different longitudinal stresses, 

 the strength of the magnetizing field being made to vary. No 

 peculiarity occurring simultaneously with the reversal of polarity was 

 observed. A more minute study was then instituted, in which the 

 nickel wires were subjected to the same treatment as the iron and steel 

 wires. 



The arrangement for twisting the wire, and the method of 

 measuring the transient current, were exactly the same as in the 

 experiment with iron, so that the further description of the process 

 will be unnecessary here. 



Two specimens of nickel wires were specially examined. The 

 one was 0.5 mm., and the other 0.43 mm. in radius. The wire was 

 carefully annealed, and deprived of residual magnetism by heating- 

 it red hot. This precaution was especially necessary with the nickel 

 wire, for if there remained but a small quantity of the residual mag- 

 netism, quite a large amount of transient current was produced. As 

 in the case of iron, the current did not attain its ultimate value 



