78 .Magnetic Galvanism. 



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Art. IX. — A new mode of developing Magnetic Galvanism, 

 which may be obtained, shocks, vivid sparks and galvanic cur- 

 rents from the Horseshoe Magnet ; by John P. Emmet, Prof, 

 of Chemistry in the University of Virginia. 



The magnetic apparatus contrived by Nobili and Antinori, and 

 by which they were enabled to obtain sparks from the horse-shoe 

 magnet, has become so familiar to the scientific reader, in conse- 

 quence of the experiments of Saxton, Faraday and Ritchie, that it is 

 deemed unnecessary to describe it more particularly, upon the pres- 

 ent occasion, than is required in order to understand the difference 

 between its construction and that which I have found to be far supe- 

 rior for the exhibition of galvanic phenomena. 



Nobili's instrument as described in the Annales de Chimie, &c. 

 consists of a coil of silk-bound copper wire, around the middle part of 

 the keeper and so confined by a spool or brass plates, as to pass readi- 

 ly between the poles of a horse-shoe magnet. The ends of this coil 

 are turned outwards in opposite directions, and so arranged as to press 

 with elasticity, upon the contiguous poles of the magnet, when the 

 keeper is on, without touching, at any time, the latter part of the ap- 

 paratus. Fig. 1 will convey a sufficiently precise idea of this ar- 

 rangement. The sparks are observed to pass between the £nds of 

 the coil, and the contiguous magnetic poles, whenever the keeper is 

 suddenly pulled ofly or restored to its place, but if 1 mistake not, 

 have never been noticed to occur between the keeper and magnet* 



It is easy to perceive that this mode of developing the galvanic flu- 

 id, is not calculated to go much beyond the immediate object which 

 it accomplished, namely the production of sparks, because both ends 

 of the copper coil being nearly -at the same time in contact with the 

 magnet, the galvanic current becomes instantaneously neutralized by 

 ' circulating through the magnet, as a conductor. Nor is it a very ad- 

 vantageous form for the exhibition of sparks, sirtce a complete fail- 

 ure, in this respect, invariably occurs, whenever both the ends of the 

 coil leave the poles of the magnet, or touch them, simultaneously ; or 

 when, from the constant and violent pulling at the keeper, one wire 

 becomes too short to reach the magnet. 



With a view of obviating these disadvantages and increasing the 

 rapidity of magnetic induction in the keeper, T made the following 

 arrangement. 



* December, 1831. 



