DISCOVERY BY MEANS OF INFERENCE. 593 



the primary cause of voltaic electricity was the oxidation 

 of the metal. Based upon facts, Grotthus in 1805, in- 

 ferred and proposed his theory of electrolysis ; and after- 

 wards Davy, Kiffault, Champre, Faraday, and Berzelius 

 formed similar theories, and the latter investigator inferred 

 that all substances chemically unite in consequence of 

 their possessing opposite electrical properties, and thus 

 was enabled to devise his well-known electro-chemical 

 series of the elementary substances and his electrical 

 theory of chemical action. As a fully-proved instance 

 and discovery by inference from known data, Ohm, in 

 1827, published his well-known formula of the quantity 

 of the voltaic current. 



As early as the year 1807, Oersted had inferred the 

 existence of a connection between electricity and magne- 

 tism, and in a book, published by him during that year, 

 he proposed ' to try whether electricity in its latent state ' 

 (i,e. as a current) ' will not affect the magnetic needle ; ' 

 but it was not until the year 1819 that he, by means of 

 experiments, actually made the discovery. By studying 

 the phenomena of Oersted's great discovery of electro- 

 magnetism, Ampere, in 1820, was led to infer that elec- 

 tric currents were themselves magnetic and attract and 

 repel each other. On testing his hypothetical inference by 

 experiments he proved it to be true, and discovered that 

 parallel currents proceeding in the same direction attract 

 each other, but if in a reverse direction, mutually repel. 

 By similar reasoning and experiment he discovered how 

 to make electro-magnets by coiling an insulated wire 

 round an unmagnetised steel -bar, and sending a current 

 through the wire ; it was in this way that the first electro- 

 magnet was made. He also inferred from the results of 

 Oersted's experiments and his own an hypothesis of the 

 mutual magnetic action of electric currents, and at once 



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