148 WRITINGS OP JOSEPH HENRY. [1839 



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 paralyze the 

 arms having been so neutralized by the interposition of a 

 plate and ribbon 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 neutralization 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 

 electrical current from a galvanic battery exerts two distinct 

 kinds of dynamic 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 induction 

 is capable also of being neutralized by the interposition of 

 a plate of metal between two conductors. The other kind 

 of induction 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 kind of 

 induction form the subject of my last paper, as well as that 

 of the previous one; while it would appear from the arrange- 

 ment of Dr. Faraday's experiments that the results detailed 

 in his first series and those in the fourteenth were princi- 

 pally produced by the second kind of induction. Although 

 I may be too sanguine in reference to the results of the dis- 

 covery, yet I cannot refrain from adding that it appears to 

 lead to a separation of the electrical induction of a galvanic 

 current from the magnetical, and that it is a step of some 

 importance towards a more precise knowledge of the phe- 

 nomena of magneto-electricity." 



* 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 induction iron acts as any other metal. 



