EFFECT OF MAGNETIZATION ON THE PERMANENT TWIST OF NICKEL. 325 



rod. It dipped into a vessel filled with water, which served to stop 

 the torsional oscillation of the wire, when the twist was released. The 

 torsion circle had a stout rod (a) for vertical axis. This was capable 

 of up and down motion by means of ratch work, and could be clamp- 

 ed by a screw. The lower end of the axis was cut, and made to bite 

 the upper extremity of the wire. The wire is shown in Fig. 2. Two 

 small pieces of thick brass plate were attached to the extremities of the 

 wire. The upper end was placed between the terminal cleft of the 

 axis, and clamped by a screwing nut, while the lower end was similar- 

 ly caught at the upper end of the cross, and fixed by a screw which 

 went through a hole in the plate, as shown in the figure. 



In front of the mirror was placed a circular scale divided into 

 half millimetres. The radius was 85.8 cm., so that one scale division 

 corresponded, when seen by reflection, to one minute of arc. The 

 scale was illuminated by gas jets, and the reflected image was observed 

 by means of a telescope. 



The magnetizing coil was 30 cms. long, ;ind gave a field of 36.7 

 C. G. S. units by passage of a current of one amj)ere. In addition to 

 the magnetizing coil, a small coil was inserted within the solenoid. 

 Through this coil, a steady current was mainttdned to compensate the 

 vertical component of the terrestrial magnetic force. The magnetizing 

 current was generally olitained from Bunsen cells, and made to vary 

 continuously by placing a liquid slide in the circuit. It was 

 measured by a Thomson graded galvanometer. The difterent parts of 

 the apparatus being as described above, the experiment was conducted 

 in the followins^ manner. 



A carefully anneided nickel wire was fixed witliin the S(3lenoid, its 

 upper end being screwed to the axis of the torsion circle, and its lower 

 end to the cross as before mentioned. While the wire was being set 

 in position, the magnetizing force was zero within the solenoid, the 



