1821.] Prof . Oersted on Electro-magnetism. 331 



site to do when treating of cylindrical conductors, they may 

 nevertheless be readily applied to conductors of other forms ; it 

 appeared to me that the simplest representation should be pre- 

 ferred. 



(D.) The Magnetic Needle. 



As fresh electricity is continually evolving in the galvanic 

 column, the discharge of it must be regarded as a continual addi- 

 tion and subtraction. The peculiar state of forces which exists 

 in the connecting wire, in which they act as electro-magnetic 

 forces, appears to me to be a state of continual agitation. But 

 in the magnet, the mode of action of the same forces differs from 

 that of electro-magnetism, in their being almost entirely in a state 

 of repose, and forming no close circle. Here we must alter 

 the denomination 4- e into that of + m, and the denomination 

 — e into that of — m. The pole of a magnet towards which + m 

 is directed ought then to produce the most marked effect of 

 + m, and the pole directed opposite to — m, ought, in the same 

 way, to exhibit the strongest effect of — m, supposing always 

 that the extension and the state of the conducting property of 

 the conductor occasion no exception. We are now speaking of 

 the effect of each point, and not of the greatest effect of the 

 whole half of a magnet, which evidently can take place only 

 opposite the end. In a certain sense it may be said that the 

 magnet is a body charged with electro-magnetism. This manner 

 of considering the magnet agrees with that generally admitted 

 from the point at which we changed the expressions from + s 

 and — e to those of + m and — m ; it may now be left without 

 further explanation. 



But it will be necessary to explain in this place the reasons 

 which prevent my adopting of M. Ampere's ingenious theory of 

 magnetism. It is well known that this philosopher supposes 

 that the line which unites the opposite poles of the magnet, is 

 surrounded with electrical currents placed in planes perpendicu- 

 lar to the axis, so that these currents, and not the longitudinal 

 magnetic distribution, are the cause of magnetism. According 

 to this idea, two neighbouring moveable magnets, would have a 

 tendency to turn in such a manner, that their circular currents 

 would attract each other. If then we place two magnets, one 

 of which at least should be moveable, one above the other with 

 their axes parallel, it must happen that the moveable needle will 

 turn, until the opposite poles are placed upon each other. A and A', 

 fig.9 f PI. XI), represent transverse sections of two magnets placed 

 upon each other in the same direction ; so that thus we see only one 

 of the currents of each magnet. The darts do not represent the 

 circular movements of the forces in the conductors (+ s and — e), 

 but the direction of the current, such as it is usually imagined to 

 be (+ E and — E). The similar letters in the two circles repre- 

 sent those places, in which the direction of the current is the 



