Bodies are repelled from the Poles of a Magnet. 271 



by the helix, or of the hehx by the cores. It is manifest that 

 the magnets can have no 'permanent effect upon the helix ; the 

 ciu'rent through the latter, measured by a tangent galvanometer, 

 is just as strong when the cores are excited as when they are 

 unexcited. The helix may certainly have an effect upon the 

 cores, and this effect is either to enfeeble the magnetism of the 

 cores or to strengthen it ; but if the former, and the bar were 

 the simple bismuth which it is when no current operates on it, 

 the action, though weakened, would still be repulsive; and if the 

 latter, the increase would simply augment the repulsion. The 

 fact, however, of the ends of the bar being attracted, proves that 

 the bar has been thrown into a peculiar condition by the current 

 circulating in the surrounding coil. Changing the direction of 

 the current in the coil, we find that the self- same magnetic 

 forces which were formerly attractive are now repulsive ; to pro- 

 duce this effect the condition of the bar must have changed with 

 the change of the current; or, in other words, the bar is capable 

 of accepting two different states of excitement, which depend 

 npon the dii-ection of the current. 



In order, however, to reduce as far as possible the action of 

 the helix upon the cores, I repeated the experiments with the 

 small helix referred to in fig. G, page 27. It will be remembered 

 that this helix is but an inch in length, and that the bismuth bar 

 is 6^- inches long. I removed the magnets further apart, so that 

 the centres of the cores were half an inch beyond the ends of the 

 bismuth bar, while the helix encircled only an inch of its central 

 portion : in this position, when the helix was excited, there was 

 no appreciable magnetism excited by it in the dormant cores ; 

 at least, if such were excited, it was unable to attract the small- 

 est soft iron nail. Here then we had cores and helix sensibly 

 independent of each other, but the phsenomena appeared as 

 before. The bar could be held by the cores against the side of 

 the helix, with its ends only a quarter of an inch distant from 

 the ends of the cores; on reversing either current the ends 

 instantly receded, but the recession could be stopped by again 

 changing the direction of the current. With a tranquil atmo- 

 sj)here, and an arrangement for reversing the current without 

 shock or motion, the bar obeyed in an admirable manner the will 

 of the experimenter, and, under the operation of the same forces, 

 exhibited all the deflections sketched in figs. 40, 41, 42 and 43. 



The motion of the bar cannot be referred to the action of 

 induced currents. The bar was brought into the centre of the 

 hollow cylinder in which it swung, and held there ; the forces 

 were all in action, and therefore all phjenomena of induction 

 passed : the arrangement of the forces being that shown in 

 Hg. 40, on releasing the bar it was driven from the cores, whereas 



