Prof. CErsted's Experivients on Diamag7ietism. 85 



magnetic matter of the needle, notwithstanding the poles 

 which it had received under the influence of the electro- 

 magnet. To discover the diamagnetic poles in this case, it is 

 necessary to employ very small pieces or blades of iron ; 

 they should not weigh more than two or three grammes. To 

 experiment with them the easier, I attached slips of zinc or 

 pieces of wood to them. By this means 1 at last arrived at 

 the conviction, that the lower part of the diamagnetic needle 

 suspended above a polar piece has the same magnetism, and 

 that its upper portion has the opposite. In experimenting on 

 this subject, 1 finally made use of a thin blade of iron, shaped 

 thus ([ , and fixed to a piece of wood. When this blade is 

 placed on the polar piece, it has in its upper part the same 

 magnetism as the polar piece, ami its lower part the opposite. 

 When the opening of the curve faces the needle, it attracts it; 

 but when the upper part is beneath, or its lower part above 

 the needle, it repels it. 



When the needle is suspended over one of the polar pieces, 

 so that the prolongation of one of the perpendicular faces of the 

 piece divides the needle into two parts, it is found that the dia- 

 magnetic poles produced by the electro- magnet extend beyond 

 the part which is above or correspondent to the upper surface 

 of the piece. In some experiments made with a needle of bis- 

 muth of 56 millims., this effect extended to nearly 14 millims. 



When the needle was divided into two equal parts by the 

 prolonged perpendicular faces, the extremity of the needle the 

 more distant from the polar piece was not polarized. 



When the electro-magnet was furnished with two polar 

 pieces placed at a distance of 48 millims., I found that the 

 same needle had diamagnetic poles in all its parts. The 

 half of the needle which was turned towards the north pole 

 had north magnetism at its lower edge, and south mag- 

 netism at its upper edge ; the other portion of the needle 

 had, under the influence of the south pole, the magnetism of 

 this pole at the lower edge, and north magnetism at its 

 upper edge. There is, therefore^ opposite magnetism in the 

 two halves of each edge, taken separately, and in each half 

 between the two edges, the upper and lower one. 



When the diamagnetic body is made to oscillate between the 

 polar faces, it does so with greater velocity the nearer it is 

 to one of the edges of this face. In one experiment in which 

 the electro-magnet was excited by sixteen of Bunsen's galvanic 

 elements, and where the distance of the polar faces was 6 

 millims., a needle of bismuth at an equal distance from the 

 upper and lower edges of these faces made twenty-five oscil- 

 lations m 30 seconds; but level with the edges, it made 



