making contact at the battery liad subsided, and the needle 

 was at'^rest, its position was determined. The spiral on the 

 magnet was now slipped off, and the deflection of the nee- 

 dle precisely observed The battery current was now broken ; 

 the connections of the terminals of the spiral interchanged, and 

 contact at the battery formed. The spiral was now again re- 

 moved from the magnet, and the deflection measured. It was 

 found that the deflections of the needle in the first and second 

 experiments gave (for the mean of 6 experiments of each) an- 

 gles sensibly equal, and that with a galvanometer readmg with 

 precision, a deflection to 15", and whose needle made about 

 three vibrations per minute. These experiments were muny 

 times repeated with the current of the battery reversed m the 

 primaiy spirals as well as in the magneto-current in the second- 

 ary spii-als, and alwavs with the same results. 



'Therefore this fact (irrespective of any theoretical considera- 

 tion) is established -.—that a definite electric current, traversmg a 

 metallic circuit in proximity to another traversed by apoiver/ul voltwc 

 current, has the same intensity whether passed in the same direction 

 as the latter or in a direction opposed to it. There is, however, no 

 doubt, a diminution in the vehcity of this current similar to 

 that observed in submarine cables ; and it will be interesting 

 and important to ascertain whether that velocity is the same m 

 a direct as in an inverse direction. At another time I propose 

 solving this question, and it would be well to reserve until 

 then any hypothesis as to the real condition of a closed circuit 

 contiguous "to another carrying a voltaic current. It has always, 

 however, appeared to me that the explanation of dynamic 

 induction given by Prof W. A. Norton (m this Jour., Jan., 

 1866,) in his paper on "Molecular Physics" affords a simpler 

 and more consistent explanation of these phenomena than any 

 heretofore framed. , , , ^^ 



Faraday (Exp. Ees. 20 and 33) has also attacked the problem 

 discussed in this paper. He introduced a small voltaic arrange- 

 ment in the circuit of the secondary wire so as to produce a de- 

 flection of 30° or 40° in the galvanometer needles, and then a 

 powerful battery was connected with the primary wire. He 

 found, that after the deflection produced by the induced current 

 had subsided, the needle resumed its former position and such 

 he found was the case whichever way the contacts were made. 

 For the following reasons I do not consider these experiments 

 sufficiently refined to have solved so delicate a problem. J^ irst, 

 from many experiments, which I have made, I have shown that 

 no voltaic combination, however constant in the usual accepta- 

 tion, can be formed so as to hold a galvanometer-needle even 

 approximately in one position for only a mmute, when it is ex- 



