226 Mr. E. H. Hall on anew Action of 



currents is electromotive force, which must be distinguished 

 from the mechanical force which is the subject of this chapter." 



This statement seemed to me to be contrary to the most 

 natural supposition in the case considered, taking into account 

 the fact that a wire not bearing a current is in general not 

 affected by a magnet, and that a wire bearing a current is 

 affected exactly in proportion to the strength of the current, 

 while the size and, in general, the material of the wire are 

 matters of indifference. Moreover, in explaining the phe- 

 nomena of statical electricity, it is customary to say that 

 charged bodies are attracted toward each other or the contrary 

 solely by the attraction or repulsion of the charges for each 

 other. 



Soon after reading the above statement in Maxwell I read 

 an article by Prof. Edlund, entitled " Unipolar Induction " 

 (Phil. Mag. Oct. 1878, or Annates de Chimie et de Physique, 

 Jan. 1879), in which the author evidently assumes that a 

 magnet acts upon a current in a fixed conductor just as it 

 acts upon the conductor itself when free to move. 



Finding these two authorities at variance, I brought the 

 question to Prof. Rowland. He told me he doubted the 

 truth of Maxwell's statement, and had some time before made 

 a hasty experiment for the purpose of detecting, if possible, 

 some action of the magnet on the current itself, though with- 

 out success. Being very busy with other matters however, he 

 had no immediate intention of carrying the investigation 

 further. 



I now began to give the matter more attention, and hit 

 upon a method that seemed to promise a solution of the 

 problem. I laid my plan before Prof. Bowland, and asked 

 whether he had any objection to my making the experiment. 

 He approved of my method in the main, though suggesting 

 some very important changes in the proposed form and 

 arrangement of the apparatus. The experiment proposed 

 w T as suggested by the following reflection : — If the current of 

 electricity in a fixed conductor is itself attracted by a magnet, 

 the current should be drawn to one side of the wire, and 

 therefore the resistance experienced should be increased. 



To test this theory, a flat spiral of German-silver wire was 

 enclosed between two thin disks of hard rubber, and the 

 whole placed between the poles of an electromagnet in such a 

 position that the lines of magnetic force would pass through 

 the spiral at right angles to the current of electricity. The 

 wire of the spiral was about -J millim. in diameter, and the 

 resistance of the spiral was about two ohms. The magnet 

 was worked by a battery of twenty Bunsen cells joined four 



