• Experiments on Diama^netisin. 235 



other, that the diamagnetic body is made to oscillate. These 

 faces we call polar faces. In all cases where I have not indica- 

 ted exceptions I have used the rectangular pieces : at the com- 

 mencement of my experiments I made use of cylindrical pieces, 

 but this form is less convenient for discovering all the circum- 

 stances which ought to be taken into consideration in these re- 

 searches. A diamagnetic needle suspended horizontally between 

 the polar faces takes, as is known, the situation called equatorial 

 which is parallel to the polar faces, but if it is raised a little above 

 the edge of the polar faces, it takes a direction perpendicular to 

 the polar faces prolonged. This position is at the same time the 

 axial ; but we see from what follows, that it is the perpendicular- 

 ity of the polar faces which is here to be regarded. This phe- 

 nomenon presents itself with remarkable readiness, which renders 

 this experiment very convenient for many diamagnetic researches. 

 On turning away the needle from its position perpendicular to the 

 faces, it oscillates back again. Its directive force goes on dimin- 

 ishing as it is raised above the polar-pieces. 



This experiment has been made with many diamagnetic bodies, 

 with bismuth, amber, nacre of pearl, the shell of the tortoise, 

 with alabaster, quills, sulphur, and pit-coal. The variation of the 

 direction observed in these experiments, is lost in proportion as the 

 polar faces are removed from one another. At a distance of sev- 

 enteen millimetres the effect was still well marked, but it is much 

 stronger at short distances. When the distance was diminished 

 so far that the diamagnetic body could not enter between the 

 polar facet) that is to say, in a position perpendicular to the polar 

 faces, the part of the effect taking place above the polar faces 

 showed itself with much force. When the diamagnetic needle is 

 suspended above the upper edge of one of the polar faces, it takes 

 equally the position called axial, perpendicular to this edge, but 

 ^ith less force than when 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 to take everywhere a 

 position perpendicular to the edge, to whose influence it is ex- 

 posed. In the case where it is exposed to the action of two 

 e( %es at the same time, it takes an intermediate position. 



Above the edge of a wedge of iron placed with its base upon 

 °ne of the poles of the electro-magnet, the needle took also a 

 position perpendicular to this edge. Upon a cylindrical polar- 

 Piece, the needle with its centre above the edge of the polar 

 fa ce, places itself perpendicularly to this face; but when at 

 some distance from the edge, it turned and took a position per- 

 pendicular to the line which might be traced parallel to the axis 

 on the highest part of the cylindrical surface. When a perforated 

 cylinder is taken for a polar-piece, if the diamagnetic needle be 

 m ade alternately to descend and rise parallel to the polar face, we 



