276 Historical Sketch of Electro-magnetism. [Oct. 



striking. These take place only when the circuit is completed: 

 those only when it is incomplete. The attractions take place 

 between the similar ends of the wires, and the repulsions between 

 the dissimilar ends ; but the electrical attractions take place 

 between dissimilar ends, and the repulsions between similar ends. 

 These take place in vacuo, but those do not. When the magnetic 

 attraction brings the two wires together, they remain in contact; 

 but when electrical attraction brings two bodies together, they 

 separate after the contact. 



These experiments are varied in several ways by M. Ampere ; 

 and the apparatus with which they were made appears from the 

 plates and description published to be very delicate, ingenious, 

 and effectual. The general results drawn up by M. Ampere 

 himself from them are: 1. That two electrical currents attract 

 when they move parallel to each other, and in the same direction ; 

 and repel when they move parallel to each other in contrary 

 direction ; 2. That when the metallic wires traversed by these 

 currents can only turn in parallel planes, each of the currents 

 tends to direct the other into a situation in which it shall be 

 parallel, and in the same direction ; 3. That these attractions and 

 repulsions are entirely different from the ordinary electrical 

 attractions and repulsions. 



On Sept. 25, M. Arago stated to the Royal Academy of 

 Sciences that he had ascertained the attraction of iron filings by 

 the connecting wire of the battery exactly as by a magnet. This 

 fact proved not only that the wire had the power of acting on 

 those bodies already magnetized, but that it was itself capable of 

 developing magnetism in iron that had not previously been mag- 

 netized. When the wire in connexion with the poles of the 

 battery was dipped into a heap of filings, it became covered 

 with it, increasing its diameter to the size of a goose quill; the 

 instant the communication was broken at either pole, the filings 

 dropped off; and the instant it was re-established, they were 

 re-attracted. This attraction took place with wires of brass, 

 silver, platina, &c. and was so strong as to act on the filings 

 when the wire was brought near them without actual contact. 

 It was shown not to belong to any permanent magnetism in the 

 wire or filings by the inactivity of both when the connexion was 

 not made with the battery ; and it was proved not to be electrical 

 attraction by the connecting wire having no power over filings 

 of copper, or brass, or over saw-dust. When soft iron was used, 

 the magnetism given was only momentary ; but on repeating the 

 experiment with some modification, M. Arago succeeded com- 

 pletely in magnetising a sewing needle permanently. 



The theory which M. Ampere had formed to account for the 

 magnetic phenomena of magnets by electrical powers only, 

 assumed that magnets were only masses of matter, around the 

 axes of which electrical currents were moving in closed curves. 

 This theory led him, when informed by M. Arago of his experi- 



