1822.] Hi$torical Sketch of Electro-magnetism. 119 



appear very extraordinary. It is first noticed that there is a 

 similarity between the natural magnet and the helice electro- 

 magnet of M. Ampere. It is also observed that owing to the 

 form of the imitation, and the properties of the wire, such a helix 

 must exhibit the properties of the two sides of the wire in a 

 separated state at its extremities. Mr. Faraday then proceeds 

 to notice the polarity of a circle formed from a portion of con- 

 necting wire, and of the helice : this he considers to be merely 

 the result of rotation. In revolving round a wire, the pole 

 describes a circle in a plane perpendicular to it, and it moves^ 

 with equal force in each part of the circle. These circles it 

 would describe round each successive portion of the wire ; but 

 let the wire be considered as bent into a ring, and it is evident 

 these circles recede from each other in the external part, while 

 in the centre of the ring they converge together and accumulate 

 in one spot just as would happen with the spirals of a bell-spring 

 if it were bent into a ring ; consequently the powers which move 

 the pole are most energetic in the centre of the ring into which 

 the wire is formed ; and though the movement has the appear- 

 ance of attraction on one side of the ring, and of repulsion oa 

 the other, it is always that of rotation ; hence the production of 

 what are called poles ; and the transition from the poles of a 

 ring to the poles of helices are clearly made out. 



This explanation of the electro- magnet is then followed by 

 experimental illustrations, and it is afterwards compared with 

 the common magnet; the accordance Mr. Faraday appears to 

 think as great ; but he nevertheless mentions some ditferences ; 

 among them are the following : The similar poles of magnets 

 repel at most distances, but if brought very near to each other, 

 they attract ; this attraction is not strong, and it differs from that 

 of dissimilar poles in not inducing any neutralizing effect. 

 Two dissimilar poles will take up a certain quantity of iron 

 filings when separate ; when together, they will not take up 

 nearly so much, but two similar poles will take up as much, and 

 even more, when together, than when separate. This effect is 

 not produced by the helice magnet. Is it not probable that the 

 effect mentioned by Mr. Faraday may result from the reciprocal 

 inductive action of the magnets upon each other? 



No success attended any of the attempts to render the proper- 

 ties of common cylinder magnets similar to those of the hehce 

 magnets. M. Ampere's experiment of directing a curved con- 

 ducting wire by the magnetism of the earth was repeated with 

 success. 



The influence of the earth's magnetism in producing the 

 effects which had been obtained by a common magnet was next 

 endeavoured to be ascertained by Mr. Faraday ; at first he was. 

 unsuccessful ; but since his first paper was published, a second 

 has appeared in the form of a note at page 416 of the Institution 

 Journal, which contains facts meriting a much more conspicuous 



