JOSEPH HENRY 199 



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 attempted, 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 suc- 

 cess might be expected. Besides their great powers these magnets 

 possess other properties, which render them important instruments in 

 the hands of the experimenter; 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 com- 

 menced, last August, the construction of a much larger galvanic mag- 

 net 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 production 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 meantime, it has been announced in the 

 117th number of the Library of Useful Knowledge, that the result so 

 much sought after has at length been found by Mr. Faraday of the 

 Royal Institution. It states that he has established the general fact, 

 that when a piece of metal is moved in any direction, in front of a 

 magnetic pole, electrical currents are developed in the metal, which 

 pass in a direction at right angles to its own motion, and also that the 

 application of this principle affords a complete and satisfactory ex- 

 planation of the phenomena of magnetic rotation. No detail is given 

 of the experiments, and it is somewhat surprising that results so in- 

 teresting, and which certainly form a new era in the history of elec- 

 tricity and magnetism, should not have been more fully described 

 before this time in some of the English publications ; the only mention 

 I have found of them is the following short account from the Annals 

 of Philosophy for April, under the head of Proceedings of the Royal 

 Institution : 



