Drs. Stewart and Schuster on a Magnetized Copper Wire. 539 



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

 magnetism has been recently changed, there appears to be a 

 temporary reversal o£ 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 strength- 

 ening 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 experi- 

 ments, in which increased resistance was observed when the mag- 

 netism 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 differ- 

 ence 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 suffi- 

 ciently 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 Eoyal Society as 

 preliminary, the correctness of which will, we trust, be confirmed 

 by the further experiments which it is our intention to make. 



