ox TUE MAGNETIZATION AND KETEXTIVENESS OF NICKEL. 305 



twisted through a definite angle by means of the twisting apparatus 

 described in the preceding pajjer. The wire was then subjected to 

 magnetizing currents of gradually increasing strengths, and the 

 amoiuit of induced magnetism measured by means of the deflection 

 of the contiguous magnetometer mirror. The details of the arranjre- 

 ment and method are as follows. 



The magnetizing cun-ent was obtained from 1-i large Daniell cells, 

 and the strength was varied continuously by means of a liquid slide. 

 A commutator, consisting of rocker and mercury pools, was included 

 in the circuit, so as to facilitate the reversing of the diminishing 

 current which was necessary for demagnetizing the wire in position. 

 The reversals were continued till the wire became magnetically 

 neutral. 



There was also an arrangement for compensating the direct 

 electromagnetic action of the magnetizing coil — a real necessity in 

 such experiments with nickel, because of the comparatively small 

 susceptibility of this metal. The arrangement consisted of a ring 

 with a few coils of wire wound round it. This ring mounted at the 

 pi'oper height on a wooden stand, which could be ukjn ed along a 

 groove cut in the plank on which the magnetometer rested, was set in 

 front of the magnetometer. The magnetizing curi-ent was led through 

 this small coil, whose distance from the magnetometer was adjusted, 

 so as to compensate the effect due to the solenoid. It was very diffi- 

 cult to set the ring exactly at the desired position, so that it 

 was generally necessary to :ipply small c(jrrections to the readings 

 obtained. 



In the first experiment a nickel wire 1 nmi. in diameter and -10 

 cms. long was previously heated red hot. This was placed in the 

 masrnetizinu' solenoid and demagnetized without at first anv aiii)lica- 

 tion of longitudinal stress. The strength of tlic magnetizing field 



