Experiments with Alternating Currents. 235 



increase in resistance, but also an action depending on the 

 phase of the current. 



It was thought probable that, although the bismuth spiral 

 had no real self-induction, yet it might have something equi- 

 valent. To test this, two equal resistances were prepared 

 whose coefficients of self-induction could be varied at pleasure, 

 for description of which see Addendum III. 



By no means could complete silence be obtained when the 

 telephone and alternating current were employed ; there was 

 always a decided minimum noise. The minimum noise given 

 by the telephone was certainly diminished by the introduc- 

 tion of suitable self-induction, the amount required diminish- 

 ing with the strength of the field in which the bismuth was 

 placed. But here, again, on attempting to measure I found 

 difficulties ; for the amount required varied from time 

 to time, depending certainly on the state of the telephone 

 (proved by tampering with the diaphragm), and possibly on 

 the state of the ears, or on small peculiarities of the current. 



The resistance of the bismuth spiral was determined alone 

 and in series with an ordinary resistance, the alternating 

 current and telephone being of course employed ; the results 

 were the same in each case : if the bismuth had behaved as 

 if it had self-induction, the results would have been different. 



The bismuth spiral was replaced by an ordinary resistance, 

 and self-induction was introduced until the apparent change 

 of resistance, measured by the telephone, was equal to that 

 produced by the action of a magnetic field of certain strength 

 on the bismuth : the minimum noise was very much greater 

 than that observed when the bismuth was employed. 



Before making more experiments, I thought it advisable to 

 make up some theory as a working hypothesis. 



In the first place, it is very probable that the increase of 

 resistance with a constant current, produced by a strong 

 magnetic field, is caused by, or accompanied by, a mole- 

 cular or crystalline rearrangement of the bismuth. Again, 

 it is not unlikely that the passage of a current along the 

 bismuth may cause or require an additional rearrangement; 

 and it is possible that an arrangement which has a certain 

 resistance for one strength of current may not have the same 

 resistance for another strength. It is not suggested that 

 different strengths of current may be subject to different 

 resistances, but that the arrangement for one strength of 

 current may produce — the previous arrangement still obtain- 

 ing — a different resistance for another strength of current. 

 The changes in resistance w r ould in this case be of a compli- 

 cated character ; I worked on the above assumption, assisted 

 by mathematics, without obtaining any serviceable results. 



