84 Prof. CErsted's Experiments on Diamagnetism. 



shaped piece of iron, placed with its base on one of the poles 

 of the electro-magnet, the needle likewise assumes a position 

 perpendicular to this edge. On a cylindrical polar piece, the 

 needle placed with its centre above the edge of the polar face, 

 arranges itself perpendicular to it; but at some distance from 

 the edge it turns and takes a perpendicular position to the line 

 which may be drawn parallel to the axis in the more elevated 

 part of the cylindrical surfece. When a perforated cylinder is 

 employed as a polar piece, and the diamagnetic needle is made 

 to descend and rise alternately, and parallel to the polar face, 

 the needle is found to leave the position parallel to the polar 

 faces, and to assume the position called axial as soon as it is 

 opposite the perforations. I employed for this experiment a 

 needle of bismuth 16 millims. in length. "With two similar 

 polar pieces the same effect is obtained, but it is much greater. 



When the diamagnetic needle is suspended between the 

 polar faces, it has, in accordance with the experiments of the 

 German philosophers above-mentioned, magnetic poles in the 

 transversal direction, arranged in such a manner that the mag- 

 netism of each side is of the same nature as that of the pole 

 nearest to the electro-magnet. The easiest method of obser- 

 ving this is that described by M. Pliicker, who introduces 

 between the polar faces, and parallel to them, a small bar of 

 iron separated from the faces by some non-magnetic substance. 

 As the sides of this bar acquire by the influence magnetism 

 the reverse of that of the nearest face, but each side of the 

 needle has the same magnetism as the nearest face, the needle 

 now retained by two forces oscillates with much greater velo- 

 city than when under the influence of the polar faces only. 

 When the diamagnetic needle is raised above a polar piece, 

 and its direction is changed, its magnetic poles change their 

 places at the same time. 



I had been led into error at the commencement by several 

 phaenomena, which in the novelty of the investigation seemed 

 very complicated, but which nevertheless appeared very sim- 

 ple when the law had been found for them. At first I thought 

 that the diamagnetic needle above the polar pieces hatl in 

 each extremity the opposite magnetism to that of the adjoining 

 polar piece ; for the lower part of a bar of iron, influenced by 

 the piece, repelled the extremity of the needle which was above 

 that piece. This effect takes place not only on placing the 

 repelling pole of iron near to each side, but equally above and 

 below. Nevertheless later experiments have led me to reject 

 the conclusion which I had previously drawn. I found that 

 a piece of iron of moderate size receives from the polar piece 

 acting upon it, a magnetic force sufficient to repel the diar 



