HISTORY OF GALVANISM. 



this kind of agency, action and reaction are equal and opposite. It 

 appeared to follow almost irresistibly from these considerations, that 

 magnetism might be made to produce electricity, as electricity could 

 be made to imitate all the effects of magnetism. Yet for a long time 

 the attempts to obtain such a result were fruitless. Faraday, in 1825, 

 endeavored to make the conducting-wire of the voltaic circuit excite 

 electricity in a neighboring wire by induction, as the conductor charged 

 with common electricity would have done, but he obtained no such 

 effect. If this attempt had succeeded, the magnet, which, for all such 

 purposes, is an assemblage of voltaic circuits, might also have been 

 made to excite electricity. About the same time, an experiment was 

 made in France by M. Arago, which really involved the effect thus 

 sought ; though this effect was not extricated from the complex phe- 

 nomenon, till Faraday began his splendid career of discovery on this 

 subject in 1832. Arago's observation was, that the rapid revolution 

 of a conducting-plate in the neighborhood of a magnet, gave rise to a 

 force acting on the magnet. In England, Messrs. Barlow and Christie, 

 Herschel and Babbage, repeated and tried to analyse this experiment ; 

 but referring the forces only to conditions of space and time, and over- 

 looking the real cause, the electrical currents produced by the motion, 

 these philosophers were altogether unsuccessful in their labors. In 

 1831, Faraday again sought for electro-dynamical induction, and after 

 some futile trials, at last found it in a form different from that in which 

 he had looked for it. It was then seen, that at the precise time of 

 making or breaking the contact which closed the galvanic circuit, a 

 momentary effect was induced in a neighboring wire, but disappeared 

 instantly. 1 Once in possession of this fact, Mr. Faraday ran rapidly up 

 the ladder of discovery, to the general point of view. Instead of sud- 

 denly making or breaking the contact of the inducing circuit, a similar 

 effect was produced by removing the inducible wire nearer to or fur- 

 ther from the circuit ; 2 the effects were increased by the proximity of 

 soft iron ; 3 when the soft iron was affected by an ordinary magnet 

 instead of the voltaic wire, the same effect still recurred ; 4 and thus 

 it appeared, that by making and breaking magnetic contact, a momen- 

 tary electric current was produced. It was produced also by moving 

 the magnet ; 5 or by moving the wire with reference to the magnet.* 

 Finally, it was found that the earth might supply the place of a magnet 



1 Phil. Trans 1832, p. 127, First Series, Art. 10. " Art. 18. 3 Art. 28. 

 4 Art. 37. 5 Art. 39- 6 Art. S3 



