Galvanism, from Galvani to Ohm. 87 



inducing magnetization in iron. The question naturally sug- 

 gested itself as to whether the similarity of properties between 

 currents and magnets extended still further, e.g. whether 

 conductors carrying currents would, like magnets, experience 

 ponderomotive forces when placed in a magnetic field, and 

 whether such conductors would consequently, like magnets, 

 exert ponderomotive forces on each other. 



The first step towards answering these inquiries was taken 

 by Oersted* himself. " As," he said, " a body cannot put 

 another in motion without being moved in its turn, when it 

 possesses the requisite mobility, it is easy to foresee that the 

 galvanic arc must be moved by the magnet " ; and this he 

 verified experimentally. 



The next step came from Andre Marie Ampere (b. 1775, 

 d. 1836), who at the meeting of the Academy on September 18th, 

 exactly a week after the news of Oersted's first discovery had 

 arrived, showed that two parallel wires carrying currents 

 attract each other if the currents are in the same direction, 

 and repel each other if the currents are in opposite directions. 

 During the next three years Ampere continued to prosecute 

 the researches thus inaugurated, and in 1825 published his 

 collected results in one of the most celebrated memoirsf in the 

 history of natural philosophy. 



Ampere introduces his work by proclaiming himself a 

 follower of that school which explained all physical phenomena 

 in terms of equal and oppositely directed forces between pairs 

 of particles ; and he renounces the attempt to seek more 

 speculative, though possibly more fundamental, explanations 

 in terms of the motions of ultimate fluids and aethers. Never- 

 theless, he indicates two conceptions of this latter character, on 

 which such explanations might be founded. 



In the firstj he suggests that the ponderomotive forces 



* Schweigger's Journal fur Chem. u. Phys., xxix (1820), p. 364 ; Thomson's 

 Annals of Philosophy, xvi (1820), p. 375. t Mem. de 1'Acad., vi, p. 175. 



% facueil tF observations electro- dynamiques, p. 215 ; and the memoir just cited, 

 pp. 285, 370. 



