236 Experiments on Diamagnetism. # 



find that this needle quits its parallel position and takes an axial 

 one as soon as it is placed opposite the holes of perforation. For 

 this experiment I use a needle of bismuth of only sixteen millime- 



tres in length. In using the two polar-pieces together, you pro- 



duce the same effect in a much greater manner. 



When the diamagnetic needle is suspended between the polar 

 faces, it has, according to the experiments of the German investiga- 

 tors already cited, the magnetic poles in a transverse direction dis- 

 posed in such a manner that the magnetism of each side is of the 

 same nature as that of the nearest pole of the electro-magnet. The 

 easiest method of confirming this is that of Plucker, who intro- 

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

 of iron separated from the faces by some non-magnetic body. Since 

 the sides of this bar receive influence by magnetism opposite 

 to that of the nearest face, and also each side of the needle has 

 the same magnetism as the face nearest to it, the needle, now held 

 by two forces, oscillates with much greater rapidity than when 

 under the influence of the polar faces alone. When the diamag- 

 netic needle is raised above one of the polar-pieces, so as to change 

 its direction, its magnetic poles change their place at the same 

 time. At the beginning I had been led into error by many phe- 

 nomena, which in the novelty of the researches seemed very 

 complicated, but now appear very simple since the law is found. 

 At the commencement I believed that the diamagnetic needle 

 above the polar-piece, had in each extremity magnetism opposite 

 to that of its neighboring polar-piece ; for the lower part of a bar 

 of iron influenced by the piece, repelled the extremity of the nee- 

 die which was above the piece. I have found this effect not only 

 in placing the repelling pole of iron near each side, but equally 

 above and below. Yet the later experiments have refuted the 

 conclusions which I had drawn from the first. 1 have found that a 

 piece of iron which is not very small, receives from the polar-piece 

 that acts upon it, a magnetic force quite strong for repelling the 

 diamagnetic matter of the needle, in spite of the poles which it has 

 received by the influence exerted upon it by the electro-magnet. 



For discovering the diamagnetic poles in this case, it is neces- 

 sary to employ very small pieces or plates of iron ; generally they 

 should be bat two or three grammes in weight. In order to man- 

 age them more easily, I have attached them to plates of zinc or 

 pieces of wood. By this means I became at last convinced that the 

 lower part of the diamagnetic needle suspended above the polar- 

 piece had the same magnetism as that, and that its upper part had 

 the opposite. In experiments for this object, 1 have made use ol 

 a thin plate of iron of this form <[, attached to a bit of wood. 



When this plate is placed upon the polar-piece, it has the same 

 magnetism in its upper part as the polar-piece, and in the lower 

 part the opposite. When the opening of this curve is opposite to 



