1821.] Historical Sketch of Electro-magnetism. 275 



are of great importance. At a meeting of the Royal Academy 

 on Sept. 18, he described an experiment proving that the voltaic 

 pile itself acted in the same manner as the wire, connecting its 

 two poles ; and produced an instrument which, at the same time 

 that it proved this action, was shown to be of great use in expe- 

 riments, on currents of electricity. This was merely a magnetic 

 needle, but from the uses to which it was applied was called a 

 galvanometer. When placed near a pile, or trough, in action, 

 having its poles connected either by a wire, or by introducing 

 them into one cell, it immediately moved, becoming obedient to 

 the battery in the same manner as to the connecting wire ; and 

 the motions were such as if the battery were simply a continua- 

 tion or part of the wire. In consequence of this action, the 

 needle becomes an instrument competent to indicate that state 

 of an active voltaic pile, and the wire connecting it, which is sup- 

 posed to be occasioned by currents of electricity, and in which 

 only, magnetism has yet been discovered. 



On Sept. 25, M. Ampere announced the new fact of the 

 attraction and repulsion of two wires connecting the poles of a 

 battery; and showed, that the magnetic needle which had pre- 

 viously been used to prove the magnetic attractions and repul- 

 sions of the wire, could be replaced by another connecting wire 

 like the first. This discovery seemed to liberate the phenomena 

 of magnetism from any peculiar power resident in the magnet, 

 and to prove its production by electricity alone. When by 

 Oersted's discovery it had been shown that a wire connecting 

 the poles of a voltaic battery would act on a magnet, attracting 

 and repelling it, just as another magnet would do, it was fair to 

 assume that the wire possessed the powers of the magnet it sup- 

 plied ; and when the second magnet was replaced by another 

 connecting wire, as in Ampere's experiment, and the powers and 

 actions still remained as before, it was perfectly correct to consider 

 these powers and actions as magnetical ; so that it became evi- 

 dent that magnetism could be exerted independent of magnets, 

 as they are usually called, and of any of the means of excitation 

 usually employed, but wholly by electricity, and in any good 

 electrically conducting medium. 



The phenomena with two conductors situated between the 

 poles of the battery are as follows : When they are parallel to 

 each other, and the same ends of them are similarly related to 

 the battery ; i.e. when the supposed currents existing in them 

 are in the same direction, then they attract each other; but if the 

 opposite ends be connected with the battery, so that the currents 

 conceived to exist in them are in opposite directions, they repel 

 each other. If, also, the one being fixed, the other be moveable, 

 mid the currents be sent, or the connections be made in opposite 

 directions, then the moveable one will turn round until they are 

 in the same direction. The contrast between these attractions 

 and repulsions, and those usually called electrical, are very 



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