1822.] Historical Sketch of Electro-magnetism. 113^ 



were but one only, which is to be called the electrical cnrrettt, 

 without any reference to positive or negative, and which is con- 

 sidered as moving in the battery from the copper to the zinc end, 

 and in the wire from the zinc to the copper end. It is evident 

 that thus modified, the existence of the current, and its direction, 

 are assumed simply for the convenience of having something to 

 which the direction of the electro-magnetical motions may readily 

 be referred ; and, consequently, when thus spoken of, no refer- 

 ence is made to the way in which the double current exists in 

 the wire, or to the cause of the production of magnetism by it. 



In the historical sketch I have already given you of the facts 

 as they were discovered, I mentioned that M. Oersted first ascer- 

 tained the mutual action of the wire and the magnetic needle. 

 He showed that the apparatus had power over the needle only 

 when the connexion was completed, consequently the electricity 

 must be in progressive motion, or forming a current, as M. Am- 

 pere states, before it can become magnetic. M. Ampere, then, 

 discovered the fact that two electrical currents (using the word 

 in his own sense) were capable of acting on each other, and pro- 

 ducing entirely new electrical phenomena. This discovery was 

 noticed in the former part of this letter,* and it was mentioned 

 that when the currents were in the same direction, they 

 attracted each other ; when in different directions, they repelled 

 each other. These attractions and repulsions differ entirely 

 from those exhibited by electricity in a state of tension, as may 

 be seen by referring back to the account given of them. M. 

 Ampere nevertheless considers them as belonging to the electri- 

 city, but only when it moves in currents. They are, he thinks, 

 dependent on certain properties which these currents possess, 

 and are not produced by the action of any magnetic or other 

 fluid which the electricity has set at liberty. Electricity, when 

 accumulated, has the power of causing certain attractions and 

 repulsions which are called electrical ; when in motion it has the 

 powder of causing certain other attractions and repulsions; 

 namely, those in question. 



Having then ascertained these new^ properties of electric cur- 

 rents, M. Ampere, in the progress of his reasonings, reverted 

 back to Oersted's experiment, and removing one of the currents, 

 he substituted a magnet in its place. The results were the same 

 as before ; the attractions and repulsions were of the same kind, 

 and took place in the same manner ; so that the effects which 

 were known to be electrical with the two wires, were produced', 

 when in place of one of them a magnet was used : only, the dis^- 

 tribution of the powers in the magnet seemed to differ from that 

 in the wire or current ; for that power which is exhibited by one 

 side of the wire is concentrated in one end of the magnet, and 



* Annah of Philosophy, vol. ii, p. ST 5, New Series. 



Neiv Series, v o l . 1 1 1 , i 



