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apparent opposition to this, found that not the least difference in effect 

 is produced, whether the space between the conductors is occupied 

 with a conductor of electricity or not, provided the interposed sub- 

 stance be not of the magnetic kind. A series of experiments was in- 

 stituted to discover the cause of the discrepancy; and it was found, 

 that in the case of induction produced by the motion of a helix to- 

 wards a galvanic current,- no screening influence was indicated by 

 the deflections of the needle of a galvanometer; also, when the in- 

 duction was effected by moving a battery up and down in the acid, 

 and in the case of magnetic electricity produced by the motion of the 

 keeper towards the poles of a magnet, the interposition of the plate of 

 metal produced no change in the indications of the needle. The in- 

 duced electricity — which is thus produced by motion, and is of such 

 low intensity as only to affect the galvanometer, which does not cause 

 shocks, and is not neutralized by a plate of metal — was at first thought 

 to be of a different kind from that induced by the sudden ending of a 

 galvanic current. In reference to this idea, a new examination was 

 made of the phenomena of the screening influence of the plate, in the 

 case of the induction at the making and breaking of a galvanic cir- 

 cuit, and it was found, that the neutralizing effects, described in Prof. 

 Henry's last paper, only existed in reference to the shock, and the 

 power of magnetizing steel needles, while the indications of the gal- 

 vanometer were not at all influenced by the presence of the plate: 

 also, that the shock and deflections of the needle appeared to depend 

 on entirely different conditions, and gave, in almost every case, very 

 different indications of the amount of inductive action. Thus, in the 

 arrangement of an apparatus, which gave an intense shock at the 

 breaking of a galvanic circuit, and a very feeble one at the making 

 of the same, the deflections of the needle were as great in the latter 

 case as in the former. It was also found, that although the shock, 

 from the currents of the third and fourth orders, was very severe, yet 

 the galvanometer was scarcely moved by them. 



From all these results, Prof. Henry was at first inclined to believe, 

 that there were two kinds of electro-dynamic induction, or that the 

 induced current consisted. of two parts, one of which could be neu- 

 tralized by a plate, and the other not ; but after an attentive study of 

 the whole subject, he was led to conclude, that these facts, as well as 

 all those belonging to galvanic induction, given in his former papers, 

 could be referred to the simple laws of the induction in different di- 

 rections at the moment of making and breaking a galvanic circuit. 



