1921.] Historical Sketch of Electro-magnetism. 281 



exciting the electricity, but constantly to accompany it when 



movino" 



In consequence of M. Ampere's theory, which attributed the 

 powers of magnets to electrical currents, and also of the views 

 taken of the manner in which it was supposed that currents of 

 electricity in the connecting wire induced currents in steel bars 

 placed near them, as in M. Arago's experiments ; it was earnestly 

 hoped and expected that such an arrangement might be made 

 of magnets, wires, &c. as to produce the decomposition of water, 

 or some other electrical effects ; for as electricity produced mag- 

 netism, it was considered that magnetism might produce elec- 

 tricity. Many arrangements were made of magnets together, 

 and of wire about and round magnets ; and at first it was stated 

 that electrical effects, such as the decomposition of water, 

 attractions, &c. had been produced ; but on Nov. 6, M. Fresnel, 

 who had been very earnest in his endeavours to obtain these 

 effects, allowed to the Royal Academy that the appearances were 

 not such as to authorize the conclusion, that any certain effect 

 had been obtained. 



On the same sitting, also (Nov. 6), M. Ampere noticed an 

 effect produced by the connecting wire bent into a helix. This 

 may be easily understood from considering that the direction of 

 the magnetic power is always perpendicular to the conducting 

 wire. When, therefore, the conducting wire is parallel to the 

 axis of the helix, the power is perpendicular to that axis ; when 

 the wire forms a circle round the axis, in a plane perpendicular to 

 it, the power is in the direction of the axis ; but when, as in the 

 helix, it passes round the axis in a direction intermediate 

 between parallelism and perpendicularity, the direction of the 

 power is of course inclined accordingly. In this case the power 

 may be considered as composed of two portions, one perpendi- 

 cular to the axis, the other parallel to it. As M. Ampere con- 

 sidered magnets to be assemblages of currents perpendicular to 

 their axes, he wished, in his imitation of them, to do away with 

 that effect due to the extension of the wire in the direction of the 

 axis of the helix, and succeeded in this by making the wire at 

 one end return through the helix so as not to touch it in any part; 

 for in this position, its magnetic effects being contrary to those 

 belonging to the length of the helix, and also near to them, they 

 neutralized or hid each other. An imitation of a magnet was 

 now made by forming a helix, and making the wires at the 

 two extremities return through the centre of the helix half way, 

 and then pass out upwards and downwards, so as to form a per- 

 pendicular axis on which the whole might move. The extremity 

 of a battery being connected with these two ends of the wire, 

 the helix became magnetical, and was attracted and repelled by 

 a magnet precisely as a real magnet would have been. 



Al A I . liuch, of Frankfort, in repeating Oersted's experiments, 

 Oct. '22, added nothing new to them; but the apparatus they 



