CRYSTALLINE POLARITY AND MAGNECRYSTALLIC CONDITION OF BISMUTH. 3 
about a given line, in which, at last, it settled ; and if moved out of that position it 
returned, when at liberty, into it ; pointing with considerable force, and having its 
greatest length axial. 
2460. Another piece was then selected, having a flatter form, which when subjected 
to the magnetic power, pointed with the same facility and force, but its greatest 
length was equatorial : still the line according to which the cubes tended to associate 
diametrally, was, as before, in the axial direction. Other pieces were then taken of 
different forms, or shaped into various forms by rubbing them down on stone, but 
they all pointed well ; and took up a final position, which had no reference to the 
shape, but was manifestly dependent on the crystalline condition of the substance. 
2461. In all these cases the bismuth was diamagnetic, and strongly repelled by 
either magnetic pole, or from the axial line. It was affected only whilst the magnetic 
force was present. It set in a given constant position perfectly determinate ; and, if 
moved, always returned to it, unless the extent of motion was above 90°, and then 
the piece moved further round and took up a new position diametrically opposed to 
the former, which it then retained with equal force, and in the same manner. This 
phenomenon is general in all the results I have to refer to, and I will express it by 
the word diametral : — diametral set or position. 
2462. The effect occurs with a single magnetic pole, and it is then striking to ob- 
serve a long piece of a substance, so diamagnetic as bismuth, repelled, and yet at the 
same moment set round with force, axially or end on, as a piece of magnetic substance 
would do. 
2463. Whether the magnetic poles employed (2458.) are pointed, round, or flat- 
faced, still the effect on the bismuth is the same : nevertheless, the form of the poles 
has an important influence of a subordinate kind ; and some forms are much more 
fitted for these investigations than others. When pointed poles are employed, the 
lines of magnetic force (2149.) rapidly diverge, and the force itself diminishes in in- 
tensity to the middle distance from each pole. But when flat-faced poles are used, 
though the lines of power are curved and vary in intensity at and towards the edges 
of the flat faces, yet there is a space at the middle of the magnetic field where they 
may be considered as parallel to the magnetic axes, and of equal force throughout. 
If the flat faces of the poles be square or circular, and their distance apart about 
one-third of their diameter, this space of uniform power is of considerable extent. 
In my experience the central or axial portion of the magnetic field is sensibly weaker 
than the eircumjacent parts ; but, then, there is a small screw-hole in the middle of 
each pole face, for the attachment of other forms of termination. 
2464. Now the law of action of bismuth, as a diamagnetic body, is, that it tends to 
go from stronger to weaker places of magnetic force (2267. 2418.) ; but as a magne- 
crystallic body it is subject to no effect of the kind ; and is as powerfully affected by 
lines of equal force as by any other. So a piece of amorphous bismuth, suspended 
in a magnetic field of uniform power, seems to have lost its diamagnetic force alto- 
B 2 
