* 



400 Electro-Magnetic Expert merits 



APPENDIX.* 



?/ the ■principle of the galvanic multiplier to 



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t 



For a long time after the discovery of the principal facts in electro- 

 magnetism, the experiments in this interesting department of science 

 could be repeated only by those « ho were so fortunate as to possess 

 a large and expensive galvanic apparatus. Mr. Sturgeon, of Wool- 

 wich, did much towards making the subject more generally known, 

 by shewing that when powerful mngnets are used, many of the most 

 interesting experiments can be performed with a very small galvanic 

 combination. His articles of apparatus, constructed on this princi- 

 ple, are of a much larger size, and mor-e convenient, than any before 



used. They do not however, form a complete set, as it is evident, 



that strong magnets cannot be applied to every article required, and 

 particularly to those intended to exhibit the action of terrestrial mag- 

 netism on a galvanic wire, or the operation of two galvanic wires on 



each other. 



In a paper, published in the Transactions of the Albany Institute, 

 June, 1828, I described some modifications of apparatus, intended to 

 supply this deficiency of Mr. Sturgeon, by introducing the spiral 

 coil on the principle of the galvanic multiplier of Prof. Schweiger, 

 and this I think is applicable in every case where strong magnets can- 

 not be used. The coil is formed by covering copper wire, from n 



I'll 



to f ^ of an inch in diameter, with silk ; and in every case, which will 

 permit, instead of using a ningle conducting wire, the effect is multi- 

 plied by introducing a coil of this wire, closely turned upon itself. 

 This will he readily understood by an example : thus, in the < -pen- 

 ment of Ampere, to shew the action of terrestrial magnetism on a il- 

 vanic current, instead of using a short single wire suspended on stee 

 points ; 60 feet of wire, covered with silk, are coiled so as to form a 

 ring of about 20 inches in diameter, the several strands of which are 

 bound together by wrapping a narrow silk ribbon around them, ine 

 eopper and zinc of a pair of small galvanic plates are attached to tne 

 ends of the coil, and the whole suspended by a silk fibre, with the 



* This article arrived too late for insertion in its proper place : its importance in- 

 duces us to give it in an appendix. 



t The term galvanic element is used in this paper to denote a single pair o gi 



vanic plates. 



erroneously mentioned as 



ntier 



being connected with the Rensselaer School at Troy. 



