498 Prof. J. Henry's Contributions 



of a plate of any metal, except iron, between the conductors. 

 The other part is of considerable intensity, is not intercepted 

 by a drop of water, developes the magnetism of hardened steel, 

 gives shocks, and is screened or nentralized by a closed coil, 

 or a plate of any kind of metal. Also, the induced current 

 produced by moving a conductor towards or from a battery 

 current, and that produced by the movement up and down 

 of a battery in the acid, are of the nature of the first-men- 

 tioned part, while the cui'rents of the third, fourth, and fifth 

 orders partake almost exclusively of the properties of the se- 

 cond part. 



53. The principal facts and conclusions of this section were 

 announced to the Society in October 1839, and again pre- 

 sented in the form in which they are here detailed in June 

 last. Since then, however, 1 have had leisure to examine the 

 subject more attentively, and after a careful comparison of 

 these results with those before given, I have obtained the 

 more definite views of the phaenomena which are given in the 

 next section. 



Sect. III. — Theoretical Coiisiderations relating to the Phceno- 

 mena described in this and the preceding Communications. 

 Read November 20, 1 840. 



54-. The experiments given in the last No. of my contribu- 

 tions were merely arranged under diiFerent heads, and only 

 such inferences drawn from them as could be immediately de- 

 duced without reference to a general explanation. The ad- 

 dition, however, which I have since made to the number of 

 facts, affords the means of a wider generalization : and after 

 an attentive consideration of all the results given in this and 

 the preceding papers, I have come to the conclusion that they 

 can all be referred to the simple laws of the induction at the 

 beginning and the ending of a galvanic current. 



55. In the course of these investigations the limited hypo- 

 theses which I have adopted have been continually modified 

 by the development of new facts, and therefore my present 

 viev/s, with the further extension of the subject, may also re- 

 quire important corrections. But I am induced to believe, 

 from its exact accordance with all the facts, so far as they 

 have been compared, that if the explanation I now venture 

 to give be not absolutely true, it is so, at least, in approxima- 

 tion, and will therefore be of some importance in the way of 

 suggesting new forms of experiment, or as a first step towards 

 a more perfect generalization. 



.50. To render the laws of induction at the beginning and 

 the ending of a galvanic current more readily applicable to 



