446 MEMORIAL OF JOSEPH HENRY. 



vanic current can be employed to produce both heat and mechan- 

 ical force, it follows that if it could be produced and kept up by 

 simply inserting a permanent magnet in a coil of wire we should 

 have a machine working without any supply of power. Since it 

 can hardly be supposed that these experimenters would have hoped 

 to realize the perpetual motion, the direction in which their efforts 

 were prosecuted could have been taken only through a failure to 

 grasp the proper principles. These principles once apprehended, 

 it would have been obvious that either the project of producing 

 electricity from magnetism must be given up, or the production 

 must be accompanied by motion or change in the magnet. The 

 latter idea being grasped, success would at once have been assured. 

 It happened, however, that the experiments pursued in a wrong 

 direction necessitated this motion or change, because the magnet had 

 to be moved to get inside the coil, or magnetism had to be produced 

 in it in commencing the experiment. 



In 1831, Faraday and Henry were independently working 

 upon the problem. The former was entirely successful in showing 

 how a momentary electric current could be produced by changes of 

 magnetism in a soft iron body, or by other electrical currents, before 

 Henry published anything of his work. No question, therefore, 

 can attach to Faraday's claim to priority, and on the system some- 

 times adopted no other name than his would be mentioned in a 

 history of the subject. But a more liberal principle now prevails, 

 and the propriety of giving due credit to the independent investi- 

 gator, though he may be behindhand in publishing, is very gen- 

 erally acknowledged. From Professor Henry's paper it would 

 appear that he had actually reached a similar result before Fara- 

 day's work came to his knowledge. The magnet with which elec- 

 tricity was to be excited was the soft iron armature of his great 

 galvanic magnet. A piece of copper wire thirty feet long was 

 coiled around the middle of this armature and connected with a 

 distant galvanometer. The great magnet being suddenly excited, 

 the north end of the needle was deflected 30 degrees to the west, 

 indicating a current of electricity in the helix surrounding the 

 armature. The needle soon returned to 'its former position, and 

 when the plates were withdrawn from the acid moved 20 degrees 



