WRITINGS OF JOSEPH HENRY. 



[1824- 



set; as indeed it is plain that his principle of strong magnets 

 cannot be introduced into every article required, and par- 

 ticularly into those intended to exhibit the action of the 

 earth's magnetism on a galvanic current, or the operation 

 of two conjunctive wires on each other. To form therefore 

 a set of instruments, on a large scale, that will illustrate all 

 the facts belonging to this science, with the least expense of 

 galvanism, evidently requires some additional modification 

 of the apparatus, and particularly in those cases in which 

 powerful magnets cannot be applied. And such a modifica- 

 tion appears to me to be obviously pointed out in the con- 

 struction of Prof. Schweigger's Galvanic Multiplier:* the 

 principles of this instrument being directly applicable to all 

 the experiments in which Mr. Sturgeon's improvement fails 

 to be useful; and to those only can it be successfully applied. 

 The following description of the figures in Plate If will 

 render my meaning sufficiently clear. 



Fig. 1, is an apparatus on the plan of the Multiplier, to 

 show the deflection of a large magnetic needle. It consists 

 of a coil of wire, A B, of an oblong form, about ten inches 

 in length and one and a half in width, with a small galvanic 

 element attached to each end ; the coil is formed of about 

 twenty turns of fine copper or brass wire, wound with silk. 



Fi^. 



2. 



to prevent contact, and the whole bound together so as to 

 have the appearance of a single wire. The attachment of 

 the zinc and copper is more plainly shewn in Fig. 2, which 



*See Green's Electro-Magnetism, page 30. 



f [The figures, copied from the original copper-plate illustration, are here 

 leproduced in the text for facility of reference.] 



