Experiments ivith Alternating Currents. 231 



the deflexion : when the angular displacement was in the 

 other direction, an alternating: current diminished the deflexion. 



A magnetized steel ring behaved in a similar manner ; in 

 this case I proved experimentally (indirectly) that the action 

 on the needle varied approximately as the square of the 

 alternating current ; also on resuspending the ring so as to 

 make what was previously the lower side the upper one, the 

 direction of the deflexion was reversed. An explanation did 

 not strike me at the time of experimenting, but perhaps the 

 true explanation is that, owing either to some defect in 

 homogeneity or in geometrical shape, the direction most sus- 

 ceptible to magnetization was inclined at an angle to the 

 magnetic axis. Suppose, for example, that the angle were 

 45°: since the angle which the direction most susceptible 

 ,to magnetization makes with the plane of the coils is increased 

 by an alternating current, it is obvious that the magnetic axis 

 could be rotated 45° in either direction before there was a 

 change in the direction of the deflexion produced by the alter- 

 nating current. 



Although, undoubtedly, the phenomena described above are 

 almost entirely due to magnetic causes, it was thought 

 advisable to try some experiments with a copper (non- 

 magnetic) ring. 



It must be mentioned that the Edelmann galvanometer was 

 supplied with dampers which consisted of two hollow metal 

 cylinders capable of movement to various distances from the 

 needle. The copper ring was suspended with a diameter 

 vertical and capable of rotation about that diameter ; when 

 the dampers were pushed in as far as possible, the angle be- 

 tween the plane of the ring and the plane of the coils was 

 increased by an alternating current ; when the dampers were 

 drawn out, the angle was diminished. These repulsions and 

 attractions are no doubt caused by the interactions of the 

 original alternating current in the galvanometer coils, and the 

 induced currents, of various phases, in the copper ring and 

 dampers. 



The copper ring was sawn across, so that the circle was no 

 longer complete ; the action on the ring of an alternating 

 current in the galvanometer coils was now almost negligible. 



A steel ring was sawn across, so that the circle was no 

 longer complete, and then magnetized and suspended with 

 a diameter vertical. An alternating current produced a 

 powerful action on the suspended needle, although no induc- 

 tion-currents of any importance could exist. 

 , In the preceding experiments I was troubled with slight 

 irregularities which I attributed to imperfections in the alter- 



R2 



