1832] WRITINGS OF JOSEPH HENRY 73 



ON THE PRODUCTION OF CURRENTS AND SPARKS OF ELEC- 

 TRICITY FROM MAGNETISM. 

 (Silliman's American Journal of Science, July, 1832 ; vol. xxii, pp. 403-408.) 



Although the discoveries of Oersted, Arago, Faraday, and 

 others, have placed the intimate connection of electricity and 

 magnetism in a most striking point of view, and although 

 the theory of Ampere has referred all the phenomena of both 

 these departments of science to the same general laws, yet 

 until lately one thing remained to be proved by experiment, 

 in order more fully to establish their identity; namely, the 

 possibility of producing electrical effects from magnetism. 

 It is well known that surprising magnetic results can readily 

 be obtained from electricity, and at first sight it might be 

 supposed that electrical effects could with equal facility be 

 produced from magnetism; but such has not been found to 

 be the case, for although the experiment has often been at- 

 tempted, it has nearly as often failed. 



It early occurred to me, that if galvanic magnets on my 

 plan were substituted for ordinary magnets, in researches 

 of this kind, more success might be expected. Besides their 

 great power, these magnets possess other properties, which 

 render them important instruments in the hands of the ex- 

 perimenter; their polarity can be instantaneously reversed, 

 and their magnetism suddenly destroyed or called into full 

 action, according as the occasion may require. With this 

 view, I commenced, last August, the construction of a much 

 larger galvanic magnet than, to my knowledge, had before 

 been attempted, and also made preparations for a series of 

 experiments with it on a large scale, in reference to the pro- 

 duction of electricity from magnetism. I was however at 

 that time accidentally interrupted in the prosecution of 

 these experiments, and have not been able since to resume 

 them, until within the last few weeks, and then on a much 

 smaller scale than was at first intended. In the mean time, 

 it has been announced in the 117th number of the Library 

 of Useful Knowledge, that the result so much sought after 



