MAGiNECRYSTALLIC FORCE — ITS NATURE CONSIDERED. 
33 
2597 . I also took three cubes of calcareous spar (1695.), in which the optic axes 
were perpendicular to two of the faces, of the respective dimensions of 0*3, 0’5, and 
0-8 of an inch in the side, and placed these in succession in the magnetic field, be- 
tween either flat or pointed poles. In all cases, the optic axis, if horizontal, passed 
into the equatorial position ; or, if vertical, left the cubes indifferent as to direction. 
It was easy by the method of two positions (2470.) to find the line of force, which, 
being vertical, left the mass unaffected by the magnet ; or, being horizontal, went 
into the equatorial position ; and then examining the cube by polarized light, it was 
found that this line coincided with the optic axis. 
2598. Even the horse-shoe magnet (2485.) is sufficiently strong to produce these 
effects. 
2599. I tried two similar cubes of rock-crystal (1692.), but could perceive no traces 
of any phenomena having either magneoptic, or magnecrystallic, or any other rela- 
tion to the crystalline structure of the masses. 
2600. But though it is thus very certain that there is a line in a crystal of calca- 
reous spar coinciding with the optic axis, which line seems to represent the resultant 
of the forces which make the crystal take up a given position in the magnetic field ; 
and, though it is equally certain that this line takes up its position in the equatorial 
direction ; yet, considered as a line of force, i. e. as representing the direction of the 
force which places the crystal in that position, it seems to me to have something 
anomalous in its character. For, that a directing and determining line of force 
should have, as its full effect, the result of going into a plane (the equatorial), in 
which it can take up any one of an infinite number of positions indifferently, leaves 
an imperfect idea on my mind ; and a thought, that there is some other effect or re- 
sidual phenomena to be recognized and accounted for. 
2601. On further consideration, it appears that a simple combination of the mag- 
necrystalline condition, as it exists in bismuth, will supply us with a perfect repre- 
sentation of the state of calcareous spar ; for, by placing two equal pieces of bismuth 
with their magnecrystallic axes perpendicular to each other (2484.), we have a system 
of forces whieh seems to possess, as a resultant, a line setting in the equatorial direc- 
tion. When that line is vertical the system is, as regards position, indifferent ; but 
when horizontal, the system so stands, that the line is in the equatorial plane. Still, 
the real force is not in the equatorial direction, but axial ; and the system is moved 
by what maybe considered deplane of axial force (resulting from the union of the two 
axes at right angles to each other), rather than by a line of equatorial force. 
2602. Doubtless, the rhomboid or cube (2597.) of calcareous spar is not a com- 
pound crystal, like the system of bismuth crystals just referred to (2601.); but its 
molecules may possess a compound disposition of their forces, and may have two or 
more axes of power, which at the same time that they cause the crystalline structure, 
may exert such force in relation to the magnet, as to give results in the same manner, 
and of the same kind, as those of the double crystal of bismuth (2601.). Indeed, 
MDCCCXLIX. F 
