Magnetism on a permanent Electric Current. 327 



in opposite directions through the coils of a differential galva- 

 nometer, were so adjusted that their combined action produced 

 no effect upon the needle. A third spiral, similar to the others 

 and itself bearing a current, -was now brought near one of 

 these, and the galvanometer was observed. No permanent de- 

 flection of the needle was detected ; and therefore no perma- 

 nent action of one current on the other was discovered. I have 

 not had access to the original article, and cannot say what the 

 author's theory of the experiment may have been. The method 

 of attacking the problem seems, however, to have been similar 

 in principle to that which I at first adopted, viz. an endea- 

 vour to increase the resistance experienced by an electrical 

 current by diverting it from its normal course through the 

 conductor. 



Another research in this direction mentioned by Wiedemann 

 Avas that of Mach *. This investigator covered a circular disk 

 of silver leaf with wax, and applied the poles of a battery 

 to points diametrically opposite each other on the circumfer- 

 ence of the disk. The silver leaf becoming heated by the cur- 

 rent, the wax began to melt, and melted most rapidly where 

 the current was strongest, thus roughly showing the distribu- 

 tion of the stream. The plate, still bearing the current, was 

 now subjected to the action of an electromagnet; but no change 

 could be detected in the behaviour of the melting wax, the cur- 

 rent remaining apparently unchanged in its course through the 

 disk. This experiment, therefore, like the preceding, was nega- 

 tive in its indications. 



A recent number of the Beihldtter zu Wiedemann's Anna- 

 len mentions, in connexion with the researches of Feilitzsch 

 and Mach, another by Goref. The latter took a wire bifur- 

 cated throughout a part of its length, and passed through it a 

 current sufficiently strong to raise both branches to a white 

 heat. He then endeavoured, by means of a magnet, to divert 

 the current somewhat from one branch of the wire and draw 

 into the other branch more than its normal share. It was 

 thought that an unequal division of the current might show 

 itself by a change in the appearance of the white-hot branches. 

 No change of this kind could be detected ; and the investigator 

 therefore concluded that the action known to take place be- 

 tween conductors bearing currents was not an action between 

 the electric currents as such. Gore expressly states that he 

 undertook this experiment not knowing that any previous in- 

 vestigations with the same aim had ever been made. 



* Carl's Reperturium, vol. vi. p. 10 (1870). 



t " On the Attraction of Magnets and Electric Currents/' Phil. Mag. 

 [IV.] vol. xlviii. p. 3 ( J-3 (1874). 



