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In this paper Prof. Henry has collected such parts of his researches 

 as particularly relate to the induction at the moment of making and 

 breaking a galvanic circuit, and presents them as the continuation, 

 and, in a measure, as the completion of this part of the general sub- 

 ject of his " Contributions." 



The paper is divided into three sections : the first of these relates 

 to the induction at the beginning of a galvanic current. It will be 

 recollected that the arrangement of apparatus employed in the last 

 series of experiments produced a powerful shock at the moment of the 

 ending of the current ; but a very feeble one at the beginning. In 

 order, therefore, to study the induction in the latter case, the attention 

 of Prof. Henry was first directed to the discovery of some means by 

 which its intensity could be increased, and after some preliminary ex- 

 periments, the desired result was obtained, by using a compound Da- 

 niel's battery, instead of the single battery before employed. It was 

 also found, that the shock could be increased by diminishing, within 

 certain limits, the length of the primary conductor. 



After detailing a number of new facts relative to the induction at 

 the beginning as well as at the ending of a galvanic current, an ac- 

 count is given of the production of currents, of different orders, from 

 the beginning induction. These are found to be of the same nature 

 as the several currents produced by the induction at the ending of the 

 current, as described in Prof. Henry's last paper — each induced cur- 

 rent possessing the property of inducing a current in an opposite di- 

 rection to itself: and hence a series of alternating currents is exhi- 

 bited in the case of this induction, similar to that described in Prof. 

 Henry's last communication in reference to the ending induction. 

 The same neutralizing effect is also produced by the interposition of 

 a plate of metal between the conductors of the different orders. 



The second section relates to a class of phenomena which at first 

 sight would appear to indicate the existence of two kinds of electro- 

 dynamic induction. A brief account of the principal part of these 

 has been given in the Proceedings of the Society for Oct. 1839. The 

 attention of Prof. Henry was directed to this part of his investigations, 

 by a statement in the 14th series of Dr. Faraday's researches, which 

 was apparently in contradiction to one of the most important facts 

 given in the last number of his " Contributions." It is stated in sub- 

 stance, in Prof. Henry's last paper, that when a plate of metal is inter- 

 posed between the coil, and a helix placed above it to receive the in- 

 duction, the shock is almost entirely neutralized. Dr. Faraday, in 



