538 Br. Silvanus P. Thompson on a 



sort of temporary magnetism might have been more reasonable. 

 But Ampere had himself already been looking for a possible 

 inductive effect ; nor was he alone in the idea that such might 

 exist. Fresnel had on November 6th, 1820, announced to 

 the Academy of Sciences that he had decomposed water by 

 means of a magnet which was laid motionless within a spiral 

 of wire. Emboldened by this announcement, Ampere re- 

 marked that he too had noticed something in the way of 

 production of currents from a magnet. But before the end 

 of the year these statements were withdrawn by their authors. 

 Fresnel wrote * to the Annates de Chhnip. explaining the 

 matter. He had surrounded a bar-magnet of steel with a 

 spiral of iron wire, the ends of which dipped into water ; and 

 what he had announced on November 6th was that he had 

 found one end of the iron wire to be discoloured and oxidized, 

 while the other became covered with minute bubbles. He 

 now finds that the announcement was premature, that the 

 effects were not sustained by repeating the experiment, and, 

 further, he says he does not believe in the success of Bitter's 

 much earlier attempts to decompose water by a magnet. On 

 behalf of M. Ampere, he added that the latter had indeed found 

 little movements of a magnetic needle by bringing near it a 

 circuit of copper wire (laiton) of which a portion was coiled 

 in a spiral around a magnet, but that these movements were 

 not repeated in any constant manner. Further, that these 

 movements were, moreover, so feeble that Ampere would not 

 have published the experiments if the success of Fresnel's, 

 which he thought certain, had not persuaded him that these 

 small agitations were occasioned also by an electric current 

 resulting from the action of the magnet on the spiral in which 

 it was enveloped. 



This having occurred in 1820, it is clear that when making 

 the Geneva experiment in 1822 Ampere must have had before 

 him the possibility of induced currents, and chose rather the 

 explanation of a temporary magnetism conferred on the 

 copper loop. 



Others in the meantime had tried to repeat Fresnel's 

 observation, and found it erroneous. 



Gilbert f, after giving an abstract of Fresnel's reputed 

 discovery, says that he repeated the experiment without 

 finding any discoloration of the iron wire, and concluded that 



* Ann. Chim. Phys. xv. 1820, pp. 219-222, " Note sur des Essais ayant 

 pour but de decomposer l'eau avec un aimant." 

 t Gilb. Ann. xlvi. p. 410. 



