LAWS OF MAGNETO-ELECTRIC INDUCTION. 255 



.11 this as in other experiments ; 7 and the mere motion of a wire, under 

 proper circumstances, produced in it, it appeared, a momentary electric 

 current. 8 These facts were curiously confirmed by the results in spe- 

 cial cases. They explained Arago's experiments : for the momentary 

 effect became permanent by the revolution of the plate. And without 

 using the magnet, a revolving plate became an electrical machine ;" 

 a- revolving globe exhibited electro-magnetic action, 10 the circuit being 

 complete in the globe itself without the addition of any wire ; and a 

 mere motion of the wire of a galvanometer produced an electro-dyna 

 rnic effect upon its needle. 11 



But the question occurs, What is the general law which determines 

 the direction of electric currents thus produced by the joint effects of 

 motion and magnetism ? Nothing but a peculiar steadiness and clear- 

 ness in his conceptions of space, could have enabled Mr. Faraday to 

 detect the law of this phenomenon. For the question required that he 

 should determine the mutual relations in space which connect the mag- 

 netic poles, the position of the wire, the direction of the wire's motion, 

 and the electrical current produced in it. This was no easy problem ; 

 indeed, the mere relation of the magnetic to the electric forces, the one 

 set being perpendicular to the other, is of itself sufficient to perplex the 

 mind ; as we have seen in the history of the electrodynamical disco- 

 veries. But Mr. Faraday appears to have seized at once the law of the 

 phenomena. " The relation," he says, 12 " which holds between the 

 magnetic pole, the moving wire or metal, and the direction of the cur- 

 rent evolved, is very simple (so it seemed to him) although rather diffi- 

 cult to express." He represents it by referring position and motion to 

 the " magnetic curves," which go from a magnetic pole to the oppo- 

 site pole. The current in the wire sets one way or the other, according 

 to the direction in which the motion of the wire cuts these curves. 

 And thus he was enabled, at the end of his Second Series of Researches 

 (December, 1831), to give, in general terms, the law of nature to which 

 may be referred the extraordinary number of new and curious experi- 

 ments which he has stated ; 13 namely, that if a wire move so as to 

 cut a magnetic curve, a power is called into action which tends to urge 

 a magnetic current through the wire ; and that if a mass move so that 

 its parts do not move in the same direction across the magnetic curves, 



T Second Series, Ph il. Trans, p. 163. "Art. 141. 9 Art. 150 IO Art. ItU. 

 11 Art. 171. 1>J Fust Series. Art. 114. 13 Art. 2.56264. 



