3IAGNECRYSTALL1C CONDITION OF BISMUTH — AXIALITY. 
O 
which was before horizontal in the equatorial plane, was now vertical; the piece 
again pointed, and generally with more force than before. The line passing through 
the crystal, coincident with the magnetic axis, may now be taken as the line of force ; 
and if the process of a quarter revolution in the equatorial plane be repeated, how- 
ever often, the crystal still continues to point with the assumed line of force in the 
magnetic axis, and with a maximum degree of power. But now, if the point of 
suspension be removed 90° in the plane of the axis, i. e. to the end of the assumed 
line of force, so, that when the crystal is again freely suspended this line is vertical ; 
then, the crystal presents its peculiar effect at a minimum, being almost or entirely 
devoid of pointing power, and exhibits in relation to the magnet, only the ordinary 
diamagnetic force (2418.). 
2471. Now if the power had been equatorial and polar, its maximum effect would 
not have been produced by a change of the point of suspension through 90° in the 
equatorial plane, but by the same change in the axial plane, and any similar change 
after that in the axial plane, would not have disturbed the maximum force ; whereas 
a single change of 90° in the equatorial plane, would have brought the line of force 
vertical (as in Plucker’s case of Iceland spar), and reduced the results to a mini- 
mum or zero. 
2472. The directing force, therefore, and the set of the crystal are in the axial di- 
rection. This force is, doubtless, resident in the particles of the crystal. It is such, 
that, the crystal can set with equal readiness and permanence in two diametral po- 
sitions : and that between these there are two positions of equatorial equilibrium, 
which are, of course, unstable in their nature. Either end of the mass or of its mole- 
cules, is to all intents and purposes, both in these phenomena, and in the ordinary 
results of crystallization, like the other end ; and in many cases, therefore, the words 
axial and axiality would seem more expressive than the words polar and polarity. 
In presenting the ideas to my own mind, I have found the meaning belonging to the 
former words the most useful. 
2473. On placing the metal in other positions, and therefore in a constrained con- 
dition, no alteration of the state or power of the bismuth, either in force or direction, 
is produced by the power of the magnet, however strong its enforcement or long its 
continuance. 
2474. It is difficult readily to describe the position of this force in relation to the 
crystal, though most easy to ascertain it experimentally. The form of the bismuth 
crystals is said to be that of a cube, and of its primitive particle a regular octohedron. 
To me the crystals do not seem to be cubes, but either rhomboids or rhombic prisms, 
approaching very nearly to cubes. My measurements were very imperfect and the 
crystals not regular ; but as an average of several observations, the planes were in- 
clined to each other at angles of 91^° and 88^°; and the boundary lines of a plane 
at 87^° and 92-g°. Whatever be the true form, it is manifest upon inspection, that the 
aggregating force tends to produce crystals having more or less of the rhomboidal 
