Date. 



First off. 



Dec. 16 . . 



.. .. 



„ 17 .. 



.... . . 



„ 18 .. 



.... 



„ io... 



.... 



Drs. Stewart and Schuster on a Magnetized Copper Wire. 537 



when the experiments were interrupted during the Christmas holi- 

 days ; and in all cases the first effect of putting on the magnetism 

 was a marked increase of resistance. For instance, we have— 



On first effect. Second off. 



+36 on (2) + 3 



+34on(l) +17 



+ 54on(l) + 24 



+ 33on(l) .......... -18 



- It was soon seen that this first effect had some reference to the 

 time elapsing since the last experiments were made. For instance, 

 in the above Table, we see for December 18th a marked increase 

 of resistance when the magnet was first put on ; but, on the after- 

 noon of that day, the experiments were repeated, and there was 

 no apparent increase of resistance in this first effect. Next, with 

 regard to the average effect : on Dec. 16th, 17th, and 18th, this 

 average effect of magnetism was a decrease of resistance ; but on 

 Dec. 19th there was an apparent increase of resistance when the 

 magnetism was on. We cannot say that nothing had been done 

 to the arrangement between the 18th and 19th of December that 

 might account for this change ; but whatever was done must have 

 escaped our recollection. Undoubtedly a good many experiments 

 were made during the time between the 15th and 19th of De- 

 cember, and the direction of the magnetism was frequently changed. 

 This curious anomaly, occurring unexpectedly, induced us to limit 

 our future experiments to a definite set each day. 



4. The experiments were resumed on January 7th, the arrange- 

 ment having remained untouched during the holidays. From this 

 date until January 10th inclusive, the key was taken out before 

 beginning experiments in the morning: there was no peculiar first 

 effect ; while, on the other hand, an average effect denoting a de- 

 crease of resistance came out very prominently. On January 12th 

 and 13th the key was only taken out before magnetizing, and 

 on these occasions the first effect, denoting increased resistance, 

 was sufficiently marked. 



Our method of procedure was varied in the above manner 

 up to January 27th ; and it was invariably found that, whenever 

 the key was taken out before commencing experiments, there was 

 no first effect ; but when it was kept in until before magnetizing, 

 this first effect was sufficiently marked. These experiments concur 

 in proving that the first effect has some reference to the previous 

 treatment of the wire ; but they do not prove that it is at the same 

 time connected with the putting on of the magnetism. To deter- 

 mine this point we made a set of experiments on January 22nd, 

 26th, and 27th. When the current had become constant the key 

 was taken out, but the magnetism was not put on ; and on these 

 occasions there was no first effect of the current upon itself in the 

 direction of increased resistance, but rather in the opposite direc- 

 tion. It thus appears that the first effect which increases the 



