266 H. NAGAOKA AND K. HONDA : 



from time to time checked by means of aii ampere balance. 

 The experiment was conducted in the following manner : — 



1. The circularly magnetizing- current was kept constant, 

 and the amount of twist measured by varying the longitudinally 

 magnetizing current. 



2. The longitudinally magnetizing current vvas kept constant, 

 and the amount of twist measured by varying the circularly 

 magnetizing current. 



Before each experiment, care was taken to demagnetize the 

 wire completely either longitudinally or circularly by passing an 

 alternate current of gradually diminishing intensity. 



Twid hjj varyiiKj the longitudinal field (Fig. 1). — The 

 direction of twist in iron, so long as the longitudinal magnetizing 

 field is not strong, is such that if the current is passed down the 

 wire from the fixed to the free end and the wire is magnetized with 

 north pole upwards, the free end, as seen from above, twists in the 

 direction of the hands of a watch. By keeping the circular field 

 constant, the amount of twist increases at first, till it reaches a maxi- 

 mum in a field of about 20 units ; it then goes on diminishing till it 

 ultimately changes the direction and continues to twist in the oppo- 

 site direction witii increasing field. The field at which the twist is 

 reversed increases with the circularly magnetizing field. In nickel, 

 the direction of twist is opposite to that in iron, but the general 

 feature is similar to iron, the only difterence being that even 

 in strong longitudinal fields, the twist is not reversed. For wires 

 of the equal thickness, the amount of twist in nickel is greater 

 than that in iron — the maximum twist in iron wire of 1 mm. 

 diam. by passing 6 amperes through it amounts to about 28" 

 })er cm., while with nickel wire of 0.83 mm. diam. under similar 

 conditions, the maximum twist amounts to about 200." 



