1874.] on a Magnetized Copper Wire. 315 



In the third place, when, in a solid circuit, the direction of the mag- 

 netism has been recently changed, there appears to be a temporary 

 reversal of the average effect, which appears, at first, as an increase of 

 resistance. Besides the evidence herein detailed, we have other evidence 

 in favour of the third conclusion ; for in some preliminary experiments, 

 in which we frequently reversed the poles, we found an increase of 

 resistance when the magnetism was on. "We have given, in a Table 

 appended to this paper, a synopsis of our various experiments. 



8. We are led to conclude, from other experiments besides these, that 

 the effect of the magnetism is not merely confined to the part of the copper 

 wire wound round the poles, but is propagated all along the wire. On 

 December 2nd, for instance, the current was passed through the wire, 

 the galvanometer being joined as a secondary circuit. The main current 

 was therefore measured. 



The deflections were as follows : 



297 off 300 .off 



300 (1) 302 (1) 



297 off 301 off 



300 (1) 



This shows an average strengthening of the current, equal to about 

 one two -hundredth part of the whole. Were this strengthening due to 

 merely the change of resistance of that part of the wire wound round 

 the poles, the effect, as measured by the much more delicate arrangement 

 of Wheatstone's bridge, would be much larger than was actually observed. 



9. Allusion was made in article 7 to some preliminary experiments, in 

 which increased resistance was observed when the magnetism was put on 

 (1) and (2) alternately. Similar experiments were made, giving the 

 same result with a piece of coke and graphite, which were placed between 

 the poles of the magnet. 



10. We have also some evidence that a copper wire, one end of which 

 is wound round the pole of the magnet, changes its position in the 

 electromotive series. Two copper wires were dipped into dilute nitric 

 acid and connected with the galvanometer. A weak current passed 

 through the galvanometer owing to a slight difference in the copper wires, 

 one of which was also connected with the copper wire wound round the 

 magnet. When the magnet was on, the current, as a rule, changed in 

 intensity ; but the effect was small, and the difficulty of having two 

 copper wires which, when joined together and dipped into nitric acid, 

 give a current sufficiently weak and constant, prevented us from getting 

 any decided results. 



11. In conclusion we have to state that we regard these results which 

 we have ventured to bring before the Royal Society as preliminary, the 

 correctness of which will, we trust, be confirmed by the further experi- 

 ments which it is our intention to make. 



