ELECTRO-MAGXETIC ACTION. 243 



otber. This latter discovery was made by M. Ampere ; and the extra- 

 ordinary rapidity and sagacity with which he caught the suggestion of 

 such forces, from the electro-magnetic experiments of M. Oersted, (of 

 which we shall speak in the next chapter,) well entitle him to be con- 

 sidered as a great and independent discoverer. As he truly says, 1 " it 

 bv no means followed, that because a conducting wire exerted a force 



J o 



on a magnet, two conducting wires must exert a force on each other 

 for two pieces of soft iron, both of which affect a magnet, do not affect 

 each other." But immediately on the promulgation of Oersted's ex- 

 periments, in 1820, Ampere leapt forwards to a general theory of the 

 facts, of which theory the mutual attraction and repulsion of conduct- 

 ing voltaic wires was a fundamental supposition. The supposition was 

 immediately verified by direct trial ; and the laws of this attraction 

 and repulsion were soon determined, with great experimental ingenuity, 

 and a very remarkable command of the resources of analysis. But 

 the experimental and analytical investigation of the mutual action of 

 voltaic or electrical currents, was so mixed up with the examination of 

 the laws of electro-magnetism, which had given occasion to the inves- 

 tigation, that we must not treat the two provinces of research as 

 separate. The mention in this place, premature as it might appear, of 

 the labors of Ampere, arises inevitably from his being the author of a 

 beautiful and comprehensive generalization, which not only included 

 the phenomena exhibited by the new combinations of Oersted, but 

 also disclosed forces which existed in arrangements already familiar, 

 although they had never been detected till the theory pointed out how 

 they were to be looked for. 



CHAPTER IV. 



DISCOVERY OF ELECTRO-MAGNETIC ACTION. OERSTED. 



THE impulse which the discovery of galvanism, in 1791, and tha'c 

 of the voltaic pile, in 1800, had given to the study of electricity as 

 a mechanical science, had nearly died away in 1820. It was in that 

 year that M. Oersted, of Copenhagen, announced that the conducting 



' Th<:orie des Phenom. Electrodynamiques, p. 113. 



