MEMOIK OF OERSTED. 175 



experiments liad been made with an apparatus of small energy, tlie effect of 

 ■\vliicli was not so striking as was called lor by the importance of the fact to be 

 established, I invited my friend Esmarch, judicial councillor to his Majesty^ to 

 unite with me in repealing them with a more powerfid apparatus. Wo had 

 also for associates and witnesses the Chevalier de Vlengel, MM. llauch and 

 Eeinai't, professors of natural liistory ; Jacobson, a very skillful })hysician and 

 chemist, and Zeise, professor of philosouhy. I made other experiments when 

 alone, and if these taught me an^'thing new, I took the precaution of repeating 

 them in the presence of these eminent men of science. * * * In order to make 

 the experiment, we put in connnunication the opposite poles of the voltaic appa- 

 ratus by a metallic wire, which we will call, for brevity, the conducting or con- 

 junctive wire ; and we will designate the effect which is manifqsted in this con- 

 ductor and around it during the voltaic action by the term electric conflict. 



'' Let us suppose now that the rectilinear part of this wire is horizontal, and 

 placed above and parallel to a magnetic needle freely suspended * * * the 

 latter will move in such a manner that, under the part of the conjunctive wire 

 which is nearest to the negative pole of the apparatus, it will deviate towards 

 the west. * * * If the conjunctive wire is arranged horizontally under the 

 needle, the effects are of the same nature with those which take place when the 

 wire is above the needle ; but they act in an inverse direction — that is to say, the 

 pole of the needle, under which is the part of the conjunctive Avire that receives 

 the negative electricity of the apparatus, inclines towards the east. * * * 

 It a])pcars, from the facts stated, that the electric conflict is not inclosed in 

 the conducting wire, but that it has around it quite an extensive sphere of activ- 

 ity. We may ct>nclude from the observations that this conflict acts by a vorti- 

 cal or whirling movement." 



Such was the theory of Oersted: we shall presently see that he was less 

 happy in his theory than in his expei'iment. 



In publishing the memoir of Oersted in the Annates de cliimic et de physique, 

 M. Arago added a note in which he said that the results there recorded, " how- 

 ever singular they might appear, are accom'panied by too many details to leave 

 room for any suspicion of error." He cited, moreover, the experiments of veri- 

 fication made in his presence, at Greneva, by M. de la Rive. 



^Tlie explanation proposed by Oersted for the capital fact which he bad just 

 discovered, recalled in some respects the vortices of Descartes. This did not 

 much savor of the spirit of the present epoch; it met consequently with but 

 little acceptance. At the end of barely a few weeks. Ampere had replaced it 

 by another, based on a law of attraction. I borrow the recital of this scientific 

 event from the S2")irited and learned Eloge of Ampere, read 1>y M. Arago to this 

 Academy, 21st August, 1839 : 



" The discovery of Oersted reached Paris by Switzerland. In our weekly 

 session of ^londay, 11th Se[)t(!mber, 1820, an academician who had come from 

 Geneva" (it was J\I. Arago himself) " repeated before the Academy the experi- 

 ments of the learned Dane. Seven days after. Ampere laid before us a fact 

 much more general than that of the pliysicist of Copenhagen. In so short an 

 interval of time he had divined that two conjunctive wires, that two wires 

 traversed by electric currents, would act one pn the other; he had devised 

 extremely ingenious arrangements for rendering these wires movable, without 

 the necessity of detaching the extremity of each of them from the respective 

 poles of their batteries; he had realized, transformed these conceptions into 

 instruments susceptible of operating; he had finally submitted his (capital idea 

 to a decisive exi)eriment. I know not if the vast field of })hysicsever i)resented 

 so admirabh; a discovery, conceived, made and completed with equal ra[)id<ty. 



'^ Of this brilliant discovery of Anqx're the following statem(?nt may suffice: 

 two paralhd conjiuictive wires attract each other when electricity traverses them 

 in the same direction ; tliey repel one another, if the electric currents move in 



