1831J WRITINGS OF JOSEPH HENRY. 37 



ON THE APPLICATION OF THE PRINCIPLE OF THE GALVANIC 

 MULTIPLIER TO ELECTRO-MAGNETIC APPARATUS, AND ALSO 

 TO THE DEVELOPMENT OF GREAT MAGNETIC POWER IN SOFT 

 IRON, WITH A SMALL GALVANIC ELEMENT.* 



(Silliman's American Jour, of Science, January, 1831, vol. xix, pp. 400-408.) 



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 who 

 were so fortunate' as to possess a large and expensive gal- 

 vanic apparatus. Mr. Sturgeon, of Woolwich, did much to- 

 wards making the subject more generally known, by show- 

 ing that when powerful magnets are used, many of the 

 most interesting experiments can be performed with a very 

 small galvanic combination. His articles of apparatus, con- 

 structed on this principle, are of a much larger size, and 

 more convenient, than any before used. They do not, how- 

 ever, form a complete set, as it is evident that strong mag- 

 nets cannot be applied to every article required, and partic- 

 ularly to those intended to exhibit the action of terrestrial 

 magnetism on a galvanic wire, or the operation of two gal- 

 vanic wires on each other. 



In a paper, published in the Transactions of the Albany 

 Institute, June, 1828, I described some modifications of ap- 

 paratus, intended to supply this deficiency of Mr. Sturgeon, 

 by introducing the spiral coil on the principle of the gal- 

 vanic multiplier of Prof. Schweigger, and this I think is 

 applicable in every case where strong magnets cannot be 

 used. The coil is formed by covering copper wire, from -^^ 

 to Tj^j- of an inch in diameter, with silk ; and in every case, 

 which will permit, instead of using a single conducting 

 wire, the efifect is multiplied by introducing a coil of this 

 wire, closely turned upon itself. This will be readily un- 

 derstood by an example: thus, in the experiment of Am- 



* The term galvanic element is used in this paper to denote a single pair 

 of galvanic plates. 



