332 P>'°f- Oersted on Electro-magnetism. [Nov. 



same. Now the parts which have opposite directions of the cur- 

 rent approach each other the most ; and thus they will repel each 

 other, until the needle has made half a turn, by which the cur- 

 rents are placed in a situation in which they may have parts 

 in equal directions opposite each other, which cannot take place, 

 excepting when the opposite poles shall be placed one above the 

 other. In every other parallel position of the axes, the same rela- 

 tion occurs, as may be satisfactorily conceived by imagining the 

 circles A and A' to change their places in several ways. 



S N, fig. 10, represents a magnet constructed according to this 

 idea, and the darts have the same meaning as in the preceding 

 figure, and will retain their meaning in the sequel. The direction 

 Of + E, or, according to M. Ampere, the direction of the electrical 

 current, goes always to that side which turns towards us from 

 bottom to top, as is indicated by the dart with a cross at the end, 

 placed in the middle of the magnet S N. The right face of such 

 a galvanic or electrical circle, always turns towards the north, 

 the left side towards the south. S N thus representing a mag- 

 net, the end of the right side will endeavour to turn towards the 

 north, or will be the north pole of the needle, and the end on 

 the left hand will be the south pole. S' N', fig. 10, represents 

 another needle like the former. When S', the south pole of this 

 needle, is placed opposite N, the north pole of the needle, so 

 that a, b, c, (I, of the latter are opposite a', b', c' ', df, of the 

 former, it will be readily observed that parts, the currents of 

 which have the same direction, are opposite each other, and 

 must reciprocally attracteach other, as occurs with opposite poles. 

 If, on the contrary, S' N', fig. 10, be made to act upon S" N", so 

 that N' and N" be opposite each other, and e, f, g, h, opposite 

 the points e',f, g', It', opposite currents are placed together, and 

 repel each other, as would occur with poles of similar descriptions. 



To this point the explanation is perfectly correct; but when 

 the magnets S N and S' N' are placed beside each other so that 

 the end N of the first shall be beside the end S of the other, it 

 will be conceived that the point a will be put in relation with c 

 or a' with c, or d with b' , or at last d' with b ; in all these cases, 

 these currents meet, and must repel each other. Thus the 

 theory is not in this case in unison with the phenomena. As 

 that has been said of the relation of N to S' may be applied to 

 N' and N", the requisite changes being" made. 



A true magnet acts in the same manner with respect to a 

 magnet constructed according to this idea. Let S N, fig. 1 1, 

 represent the latter, and S' N" the former ; but let S N be fast- 

 ened to one end of a thin metal plate, 1) C, provided in E 

 with a centre, and suspended like a magnetic needle. It will in 

 fact be found that N is attracted by all the points placed in the 

 interior of the circle a' , b' , <;', d' , but that it is repelled by all the 

 points placed on the exterior of the circle, as ought to happen 

 according to the theory which I have proposed, but it does not 



