135 



ing the discovery of two distinct kinds of dynamic induction^ 

 by a galvanic current. 



" Since the publication of my last paper, I have received through 

 the kindness of Dr. Faraday, a copy of his fourteenth series of expe- 

 rimental researches ; and in this I was surprised to find a statement 

 directly in opposition to one of the principal results given in my paper. 

 It is stated in substance, in the 59th paragraph of my last communi- 

 cation to the American Philosophical Society, that when a plate of 

 metal is interposed between a galvanic current and a conductor, the 

 secondary shock is neutralized. Dr. Faraday finds, on the contrary, 

 under apparently the same circumstances, that no effect is produced 

 by the interposition of the metal. As the fact mentioned forms a very 

 important part of my paper, and is connected with nearly all the phe- 

 nomena described subsequently to it, I was anxious to investigate the 

 cause of the discrepancy between the results obtained by Dr. Faraday 

 and those found by myself. My experiments were on such a scale, 

 and the results so decided, that there could be no room for doubt as 

 to their character; a secondary current of such intensity as to pa- 

 ralize the arms having been so neutralized, by the interposition of a 

 plate and riband of metal, as not to be perceptible through the tongue. 

 I was led by a little reflection to conclude that there might exist a 

 case of induction similar to that, of magnetism, in which no neutrali- 

 zation would take place; and I thought it possible that Dr.- Faraday's 

 results might have been derived from this. I have now, however, 

 found a solution to the difficulty in the remarkable fact, that an elec- 

 trical current from a galvanic battery exerts two distinct kinds of dyna- 

 mic induction : one of these produces, by means of a helix of long wire, 

 intense secondary shocks at the moment of breaking the contact, and 

 feeble shocks at the moment of making the contact. This kind of in- 

 duction is capable, also, of being neutralized by the interposition of a 

 plate of metal between the two conductors. The other kind of induc- 

 tion is produced at the same time from the same arrangement, and 

 does not give shocks, but affects the needle of the galvanometer; it is 

 of equal energy at the moment of making contact, and of breaking 

 contact, and is not affected by the introduction of a plate of copper or 

 zinc between the conductors.* The phenomena produced by the first 



* Since writing the account of the two kinds of induction, I have found that 

 the second kind, although not screened by a plate of copper or zinc, is affected 

 by the introduction of a plate of iron. In the cases of the first kind of indue 

 tion, iron acts as any other metal, 



