538 Royal Society ; — 



resistance has not only reference to the previous treatment of the 

 wire, but depends also upon the magnetism being put on. 



This result is confirmed by experiments made previous to Dec. 

 12th, in which the key was not taken out at all. For instance, 

 we have on Dec. 9th, 



First off. On first effect. Second off. 



+54 +45 



We have hitherto only spoken of the first effect obtained 

 after January 7th ; we now come to the average effect. From 

 January 7th to January 27th inclusive, the magnetism was always 

 put on in the direction (1), and the average effect invariably de- 

 noted a decrease of resistance when the magnetism was on. 



5. On January 28th the magnetism was reversed; the effect 

 during this day was very irregular. On January 29th, 30th, 31st, 

 and February 2nd the key was left in until before magnetization. 

 The first effect was now extremely large ; but it was suspected that, 

 during these experiments, the contact of the key was not very 

 good. 



On January 29th the average effect denoted a decrease of resis- 

 tance; but on January 30th, 31st, February 2nd, 4th, 6th, the 

 average effect denoted an increase of resistance. 



6. From February 6th until February 11th the wires were left 

 broken ; on February 11th there was a very slight first effect in the 

 direction of increased resistance, and a slight average effect in the 

 direction of decreased resistance. On February 12th a mercury 

 interruptor was used instead of a metal key, both the wires being 

 broken by it, and its use was continued until February 18th. The 

 interruptor was left in over night and the current was only broken 

 before magnetization, but no first effect was observed. 



From February 19th to February 26th one wire only was broken 

 by the fluid interruptor; nevertheless there was no first effect. 



On February 12th, when the fluid interruptor was first em- 

 ployed, there was a very small average effect in the direction of 

 increased resistance ; but, in all the experiments afterwards, this 

 average effect was in the direction of decreased resistance. The 

 magnetism had been in the direction (2) from January 28th ; but, 

 during the experiment of February 25th, it was reversed and 

 retained in this condition through the experiment of February 

 26th, without appearing to affect the results. 



7. From these experiments we may perhaps conclude as follows : — - 

 In the first place, there is a first effect in the direction of 



increased resistance which appears to have reference to three 

 things — namely, the previous state of the wire, the solidity of 

 the circuit, and its magnetization. 



In the second place, we have an average effect, of which the 

 normal state appears to denote a decreased resistance while the 

 magnetism is on, without reference to the direction of the mag- 

 netism. 



