296 Professor J. A. Fleming [Marcli 6, 



WEEKLY EVENING MEETING, 



Friday, March 6, 1891. 



William Crookes, Esq. F.R.S. Vice-President, in the Chair. 



Professor J. A. Fleming, M.A. D.Sc. M.BJ. 



Electro-magnetic Repulsion. 



§ 1. On the 2nd day of October, 1820, Ampere presented to the 

 Eoyal Academy of Sciences in Paris an important memoir, in which 

 he summed up the results of his own and Arago's previous investiga- 

 tions in the new science of electro-magnetism, and crowned that labour 

 by the announcement of his great discovery of the dynamical action 

 between conductors conveying electric currents.* Respecting that 

 achievement, when developed in its experimental and mathematical 

 completeness, no less a writer than Clerk Maxwell calls it " one of 

 the most brilliant in the history of physical science." Our wonder 

 at what was then accomplished is increased when we remember that 

 hardly more than two months before that date John Christian Oersted 

 had startled the scientific w^orld by the announcement of the discovery 

 of the magnetic qualities of the space near a current-traversed con- 

 ductor. Oersted called the actions going on around the conductor 

 the " electric conflict," and in his first paper,! in describing the newly- 

 observed facts, he says : — " It is sufficiently evident that the electric 

 conflict is not confined to the conductor, but is dispersed pretty widely 

 in the circumjacent space." " We may likewise collect," he adds, 

 " that this conflict performs circles round the wire, for without this 

 condition it seems impossible that one part of the wire when placed 

 below the magnetic needle should drive its pole to the east, and when 

 placed above it to the west." These few words are taken from the 

 original paper which stimulated the philosophic thought of Ampere 

 and his contemporaries, and started into existence a wave of dis- 

 covery, placing us in possession of the facts which form our starting- 

 point to-night. 



§ 2. It w ill be unnecessary to spend more than a moment or two 



♦ 'Memoire presente a I'Academie Koyale des Sciences le 2 octobre 1820, ou 

 86 tronve compris le resume de ce qui avait e'te lu a la meme Aoade'mie les 18™^ 

 et 25™® septembre 1820, sur les eftets des courants e'lectriques,' par M. Ampere. 

 See vol. XV. ' Annales de Cliimie,' 1820. 



t In the ' Annals of Philosophy ' for October 1820, vol. xvi. p. 274, is to be 

 found an English translation of Oersted's original Latin essay, dated July 21, 

 1820, describing his immortal discovery. This paper is entitled " Experiments 

 on the Effect of a Current of Electricity on the Magnetic Needle," by John 

 Christian Oersted, Knight of the Order of Danneborg, Professor of Natural 

 Philosophy in Copenhagen. 



