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LXXVI. Co7itr{hutions to Electricity mul Magnctisin. No. IV. 

 On Elecfro-dijiiamic hiduction. {Continued.) By Joseph 

 Henry, LL.D., Professor of Natural Philosophtj in the 

 College ofNetio Jersey, Priiiceton*. 



l7itroductio?i. 

 1. TN the course of my last paper, it was stated that the 

 '• investigations which it detailed were not as complete 

 in some parts as I could wish, and that I hoped to develope 

 them more fully in another communication. After consider- 

 able delay, occasioned by alterations in the rooms of the phy- 

 sical department of the college, I was enabled to resume my 

 researches, and since then I have been so fortunate as to dis- 

 cover a series of new facts belonging to different parts of the 

 general subject of my contributions. These I have announced 

 to the Society at different times, as they were discovered ; and 

 I now purpose to select from the whole such portions as re- 

 late particularly to the principal subject of my last paper, 

 namely, the induction at the beginning and ending of a gal- 

 vanic current, and to present them as a continuation, and, in 

 a measure, as the completion, of this part of my researches. 

 The other results of my labours in this line will be arranged 

 for publication as soon as my duties will permit me to give 

 them a more careful examination. 



2. In the course of the experiments I am about to describe, 

 I have had occasion to repeat and vary those given in my last 

 paper; and I am happy to be able to state, in reference to the 

 results, that, except in some minor particulars, which will be 

 mentioned in the course of this paper, Ihave found no cause to 

 desire a change in the accounts before published. My views, 

 however, of the connexion of the pha^nomena have been con- 

 siderably modified, and I think rendered much more definite 

 by the additional light which the new facts have afforded. 



3. The principal articles of apparatus used in these experi- 

 ments are nearly the same as those described in my last paper, 

 namely, several flat coils and a number of long wire helices 

 (III. 6, 7, 8.f). I have, however, added to these a constant 

 battery, on Professor Daniell's plan, the performance of which 

 has fully answered my expectations, and confirmed the ac- 

 counts given of this form of the instrument by its author. It 

 consists of thirty elements formed of as many copper cylin- 

 ders, open at the bottom, each five inches and a half in height, 

 three inches and a half in diameter, and placed in earthen 



* From the Transactions of the American Philosophical Society, vol. viii., 

 having been read .Tune 19, 1840. 



t When the numerals II. or III, are included in the parenthesis, refer- 

 ence is made to the corresponding Nos. of my contributions. 



