Prof. QErsted's Experiments on Diamagnetism. 83 



than half of this power made use of, although the greater part 

 of them might have been executed with a much weaker force, 

 even with a single element. Each extremity of the electro- 

 magnet supports a horizontal piece of iron, which we shall 

 call a polar piece. These polar pieces serve to give a hori- 

 zontal direction to the action of the electro-magnet. It is be- 

 tween the two perpendicular surfaces, which face one another, 

 that the diamagnetic tody is made to oscillate. These are 

 called polar faces. In every case, excepting those indicated, 

 I have made use of rectangular pieces. At the commence- 

 ment of my experiments I employed cylindrical pieces; but 

 this form is less suited for discovering all the circumstances 

 which should be taken into consideration in these investiga- 

 tions. 



A diamagnetic needle suspended horizontally between the 

 polar faces, assumes, as is well known, an equatorial \)OS\\\ox\^ 

 which is parallel to the polar fiices ; but if it is raised a little 

 above the edges of the polar faces, it takes a perpendicular 

 direction to the prolonged polar faces. This position is at 

 the same time axial; but it will subsequently be seen that the 

 question here is as to its perpendicularity to the polar faces. 

 This phaenomenon is exhibited with remarkable quickness, 

 which renders the experiment very convenient for many dia- 

 magnetic investigations. When the needle is turned from its 

 perpendicular position, it reacquires it by oscillation. Its di- 

 recting force diminishes with its elevation above the polar 

 pieces. The experiment was made with several diamagnetic 

 bodies, with bismuth, amber, mother-of-pearl, tortoise-shell, 

 alabaster, quills of feathers, sulphur, coal, &c. 



The change of direction observed in these experiments 

 vanishes as the polar faces are separated. At the distance of 

 17 millims. the effect was still well-marked; but it is very 

 much stronger at short distances. When the distance was 

 diminished so that the diamagnetic body could not be in- 

 serted between the polar faces, that is to say, perpendicular to 

 them, the part of the effect which takes place above the polar 

 faces was exhibited with considerable energy. When the dia- 

 magnetic needle was suspended above the upper edge of one 

 of the polar faces, it equally assumed the position called axial, 

 perpendicular to that edge, but with less force than under the 

 influence of the two faces. On examining the position which 

 the needle takes above the other edges of the polar piece, it 

 is found that it everywhere assumes the position perpendicular 

 to the edge to the influence of which it is exposed. In those 

 cases where it is exposed to the action of two edges at once, 

 it takes the intermediary position. Above the edge of a wedge- 



G2 



