40Q Electro-Ma gnetic Experiments. 



APPENDIX,* 



Oil the application of the principle of the galvanic multiplier to 

 electro-magnetic apparatus, and also to the developement of great 

 •magnetic poxccr in soft Iron, with a S7iiall galvanic element ;] by- 

 Prof. Joseph Henry, of the Albany Academy.J 



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

 jnagnetism, the experiments in this interesting department of science 

 could be repeated only by those who 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 magnets are used, many of the most 

 interesting exjieriments 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 more 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 v/ire, or the operation of two galvanic wires oa 

 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 ^'^^ 

 to 2V of an inch in diameter, with silk ; and in every case, which will 

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

 plied by introducing a coil of this wire, closely tui-ned upon itself. 

 This will be readily understood by an example : thus, in the experi- 

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

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

 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 v/hich are 

 bound together by wrapping a narrow silk ribbon around them. The 

 copper and zinc of a pair of small g-xlyanic plates are attached to the 

 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. 



I Tiie term galvanic element is used in this paper to denote a single pair of gal- 

 vanic plates, 



+ In a former number of this Journal, Prof. Henry, was erroneously mentioned as 

 l)eing connected with the Rensselaer School at Troy. 



