144 EULOGY ON AMPERE. 



the powers exercised by electricity iu motion. The general formula, 

 which gives the value of the mutual actions of the infinitely small ele- 

 ments of currents, once understood, the determination of the combined 

 actions of limited currents of diflerent forms becomes a simple problem 

 of integral analysis. Ampere did not fail to follow out these applica- 

 tions of his discoveries. He first tried to discover how a rectilinear 

 current acts on a system of circular closed currents, contained in i^lanes 

 j)erpendicular to the rectilinear current. The result of the calculation, 

 confirmed by experiment was, that the planes of the circular currents, 

 would, supposing them movable, arrange themselves parallel to the rec- 

 tilinear current. If like transversal currents pass over the whole length 

 of a magnetic needle, the cross direction which, in the experiment of 

 GSrsted, completed by Ampere, seemed an inexplicable anomaly, would 

 become a natural and necessary fact. Is it not evident, then, to all how 

 memorable would that discovery be that would rigorously establish the 

 fact that to magnetize a needle is to excite, to put iu motion around 

 each molecule of the steel, a small, circular, electrical vortex ? Ampere 

 fully realized the wide reach of the ingenious generalization that had 

 taken possession of his mind; and he hastened to submit it to exjieri- 

 meutal proofs and numerical verifications, which, iu our day, are the 

 only processes considered entirely demonstrative. 



It seemed very difficult to create an assemblage of closed circular 

 currents capable of great mobility. Ampere confined himself to an 

 imitation of this composition and form, hy causing a single electrical 

 current to circulate through a wire enveloped iu silk, and coiled like a 

 helix iu very compact spires. The resemblance between the effects of 

 this apparatus and those of a magnet was very striking, and encouraged 

 the illustrious academician to devote himself to a difficult and minute 

 calculation of the actions of closed circuits perfectly circular. 



Starting from the hypothesis that like currents exist around the i)ar- 

 ticles of magnetic bodies, Ampere, recognized, in elementary actions, 

 the laws of Coulomb. These laws treated with the most consummate 

 skill by an illustrious geometer have explained all the known facts of 

 the science of magnetism ; the hypothesis of Ampere represents them 

 with equal accuracy. 



The same hypothesis, finally applied to the investigation of the action 

 which a rectilinear connecting wire exercises over a magnetic needle, 

 leads analytically to the law that M. Biot has deduced from extremely 

 nice experiments. 



If, with the almost entire body of ancient physicists, it is thought ad- 

 visable to consider steel as composed of solid molecules, in each of 

 which exist two fluids of opposite properties, fluids combined, and neu- 

 tralizing each other when the metal is not magnetic, fluids more or less 

 separated when the steel is more or less magnetized, the theory will 

 cover all that is known at present, even in the most subtle numerical 

 particularities of ordinary magnetism. This theory is silent, ]in\:^Aver, 



