Experiments on Diamagnelism. 239 



cing the wire by a very thin particle of iron filings ; but upon in- 

 troducing in place of the iron a piece of straw which had been 

 plunged into a solution of iron, the diamagnetic effects were those 

 of attracting bodies. Nickel gives the same results as iron. Thus 

 iron and nickel ought to be called, in a strict sense, magnetic. 

 Some other bodies may be of the same kind ; I presume cobalt is. 



There is then a decreasing magnetic progression which includes 

 magnetic bodies properly so called, diamagnetic attracting bodies, 

 and diamagnetic repelling bodies. The magnetism of the last 

 may be considered as negative, if the magnetism of iron and of 

 attractive diamagnetic bodies be considered positive. 



The effect which the polar faces exert upon the attractive dia- 

 magnetic bodies is. as regards a relation to the repellants, stronger 

 when the body is placed nearer the upper or lower edges than 

 their intermediate parts. A piece of attracting glass, twenty- 

 seven millimetres long, suspended between the polar faces, at a dis- 

 tance of twenty-nine millimetres, in such a manner that the ends 

 of this needle were not farther from the polar faces than one milli- 

 metre, was oscillated each time for thirty seconds. At an equal dis- 

 tance from the upper and lower edges it made only 45 oscillations 

 in thirty seconds ; but on a level with the polar faces, it made 19. 



When the polar faces are at this distance, the needle does not 

 take the equatorial direction when it is suspended above their 

 edges. At a distance of 4 5 millimetres, it made only 5 5 os- 

 cillations. At a distance of 13-5 millimetres, it made only 2 5 

 oscillations. On approaching the polar faces even to three milli- 

 metres, the needle which now could not take the axial direction 

 between the faces, still showed all its tendency to take that posi- 

 tion; but raised at a distance of two millimetres above their 

 edges, it took the equatorial position, and made 18 oscillations in 

 thirty seconds. At a distance of three-tenths of a millimetre 

 it made 35 oscillations. At the nearest point at which it could 

 escape contact with the polar-pieces, it made 45 oscillations. 



Diamagnetic bodies, therefore, repellant as well as attractive, 

 have their oscillations more numerous in a position parallel to the 

 polar faces, than in a perpendicular one. It is to be remarked 

 here, as has already been done upon another series of experiments, 

 that the determinations of numbers have not been sufficient to 

 give the exactness necessary for calculating their laws. 



I have lately made some experiments upon the influence of 

 heat upon diamagnetic bodies. These experiments have not yet 

 heen sufficiently numerous; but they bhow that some attracting 

 diamagnetic bodies pass into the class of repellant diamagnetic by 

 an increase of temperature. The only body which has shown 

 toe this effect in a high degree, is brass. My analogous experi- 

 ments upon other bodies are not yet sufficiently decisive to be 

 reported here. 



- L 



