1874.] On a Magnetized Copper Wire. 311 



I. " Preliminary Experiments on a Magnetized Copper Wire." 

 By Professor BALFOUR STEWART, LL.D., F.R.S., and ARTHUR 

 SCHUSTER, Ph.D. Received March 30, 1874. 



1. The following experiments were made in the Physical Laboratory 

 of Owens College, Manchester. The copper wire employed (A B C D, 



see fig.) was found to contain no perceptible trace of iron, nor was it 

 sensibly magnetic, behaving quite in a neutral manner when tested by 

 the highest magnetic power at our disposal. It was covered with gutta 

 percha. The diameter of the wire was 0*0487 inch. The wire was 

 wound fifty-three times, in one direction, round the poles of a powerful 

 electromagnet, the length of wire encircling these poles being about 

 twelve metres. The direct distance of the magnet from the galva- 

 nometer, Gr, was about twelve metres. 



A Wheatstone bridge was employed, and a very delicate Thomson's 

 reflecting galvanometer by Elliott Brothers, of which the resistance was 

 5540 B.-A. units. A circuit-breaker was placed in the circuit at E, close 

 to the bridge. On some occasions, we used one consisting of a solid 

 key, which might be removed, thus breaking the circuit ; but, on other 

 occasions, a fluid or mercurial circuit-breaker was employed. 



When the left-hand pole of the electromagnet (see fig.) was made north 

 the arrangement was called (1), and when the other pole was made north 

 the arrangement was called (2). It will thus be seen, from the figure, 

 that the current went round the magnet in the same direction as the mole- 

 cular currents of arrangement (2). 



Experiments were made at intervals of two minutes ; s ad. on each 

 occasion, the current was allowed to pass through the b/idge for ten 



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