354? Mr. Faraday on certain Magneto-electrical Phenomena. 



the number of magnetic curves which can exert their induc- 

 tive influence ; and the effect in a wire of a hundred feet in 

 length will be nearly a hundred times greater than in a wire 

 of the same diameter only a foot in length. The reason why 

 a core of soft iron produces the same effect as elongation of 

 the wire, will be that it also brings magnetic curves into in- 

 ductive action exactly in the same direction as those around 

 the wire; and the rest of the circumstances, as far as I can per- 

 ceive, will accord with the cause assumed. 



That the magnetic curves of the wire carrying the current 

 shall actually affect the character of the current which gives 

 them origin, need not excite any difficulty, for this branch of 

 science shows many such cases. Ampere's experiment of 

 revolving a magnet on its own axis, and the case which I have 

 shown of drawing away electricity from the poles and equa- 

 tor of a magnet when it is revolved, are both instances of the 

 same kind. 



In conclusion, I wish to say that I think I see here some 

 of those indications of an electro-tonic or peculiar state of 

 which I have expressed expectations in the second series of 

 my Experimental Researches, par. 242.*; for though I here 

 speak of magnetism and magnetic curves for the sake of re- 

 ference, yet allowing Ampere's theory of the magnet, all the 

 effects may be viewed as effects of induction produced by elec- 

 trical currents. Hence many extensions of the experiments. 

 I have no doubt, for instance, that if a long wire were arranged 

 so as to discharge a single pair of plates, and the spark oc- 

 curring at the breaking of contact were noted, and then an- 

 other wire carrying a current in the same direction from 

 another electrometer, were placed parallel and close to but 

 without touching the first, the spark obtained on breaking the 

 contact at the first wire would be greater than before. This 

 experiment can easily be made with a double helix ; but at my 

 present distance from town I have no means of trying the 

 experiment, or of examining more closely these indications. 



I am, my dear Sir, very truly yours, 

 Brighton, Oct. 17, 1834. M. FARADAY. 



* Philosophical Transactions 1832, p. 189. 



