Experiments on Diama^netism. 237 



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the needle, it attracts it ; but when its upper part is below or its 

 lower part above, it repels it. When the needle is so suspended 

 upon one of the polar-pieces that the prolongation of. one of the 

 perpendicular faces cuts the needle into two parts, we find that 

 the diamagnetic poles produced by the electro-magnet extend 

 beyond that part which projects over the upper surface of the 

 piece. In these experiments made with a needle of bismuth of 

 fifty-six millimetres, this effect extends hardly fourteen millime- 

 tres. When the needle was cut in two equal parts by the per- 

 pendicular faces prolonged, we found that the extremity of the 

 needle most remote from the polar-piece was without polarity. 

 When the electro-magnet was armed with two polar-pieces, pla- 

 ced at a distance of forty-eight millimetres, 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- 

 ern magnetism upon its lower edge, and southern upon its up- 

 per edge ; the other half of the needle had by the influence of 

 the southern pole, the magnetism of this pole upon its lower 

 edge and of the northern upon its upper edge. 



There is then an opposition of magnetism in the two halves 

 of each edge taken separately, and in each half between the two 

 edges, the upper and lower. 



When the diamagnetic body is made to oscillate between the 

 polar faces, we find that it makes its vibrations with much more 

 strength when it is nearer one edge of this face. 



In an experiment in which the electro-magnet was acted upon 

 by sixteen of Bunsen's galvanic pairs, and where the distance 

 of the polar faces was six millimetres, a needle of bismuth being at 

 a n equal distance from the upper and lower edges of these faces, 

 made in thirty seconds twenty-five oscillations; but on a level 

 with the edges, it made in the same time one hundred oscillations. 

 Above the polar-pieces in an axial position, the needle made only 

 nineteen oscillations in the same time. These experiments have 

 been sufficiently repeated and varied to give perfect certainty to 

 what is here announced, but the researches have not yet been 

 pushed far enough to deduce an exact numerical law. 



When a horizontal needle of bismuth is suspended to the ex- 

 tremity of a balance by a thread of silk, in such a manner that it 

 ca n descend or rise, the needle is much more strongly repelled 

 when it finds itself near one of the edges of the polar faces. 

 This repulsion causes the needle to rise when it is near the up- 

 Per edges, and to descend when it is near the lower edges, and in 

 [he intermediate position it neither mounts nor descends. When 

 ^ is suspended above the polar-pieces and consequently in a di- 

 rection perpendicular to the polar faces, it is still repelled though 

 much more feebly than when in the equatorial position. 



We have hitherto known only the diamagnetic effects in bodies 

 which are repelled by the electro-magnet My experiments have 



