6 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXII.) 
shape and rhombic planes ; and that these crystals run together in symmetric groups, 
generally in the direction of their longest diameters. Now the line of magnecrystalUc 
force almost always coincides with this direction where the latter is apparent. 
2475 . The cleavage of bismuth crystals removes the solid angles and replaces them 
by planes ; so that there are four directions producing the octohedron. These clea- 
vages are not (in my experience) made with equal facility, nor do they produce planes 
equally bright and perfect. Two, and more frequently one, of these planes is more 
perfect than the others ; and this, the most perfect plane, is that which is produced at 
the most acute solid angle (2474.) ; and is generally easily recognized. When a 
bismuth crystal presents many planes of cleavage and is suspended in the magnetic 
field, one of these planes faces towards one of the magnetic poles, and its corre- 
sponding plane, if it be there, towards the other ; so that the line of magnecrystallic 
force is perpendicular to this plane: and this plane corresponds to the one which I 
have already described as being, generally, the most perfect, and replacing the acute 
angle of the crystal. 
2476 . A single crystal of bismuth was selected and cut out from the mass by 
copper tools, and the places where it had adhered were rubbed down on sand-paper, 
so as to give the fragment a cube-like form with six planes ; four of these planes 
were natural. One of the solid angles, expected to be that terminating or in the di- 
rection of the line of magnecrystallic force, was removed, so as to expose a small 
cleavage plane, which was bright and perfect, as also was expected. When suspended 
in the magnetic field with this plane vertical, the crystal instantly pointed with con- 
siderable force, and with the plane towards either one or the other magnetic pole ; 
so that the magnecrystallic axis appeared now to be horizontal and acting with its 
greatest power. When this axial line was made vertical, and the plane therefore 
horizontal, the position being carefully adjusted, the crystal did not point at all. 
Being now suspended in succession at all the angles and faces of the cube, it always 
pointed with more or less force ; but always so that a line drawn perpendicularly 
through the indicating cleavage plane (representing therefore the line of force) was in 
the same vertical plane as that including the magnetic axis : and, finally, when the 
bright cleavage plane was horizontal and the line of directive force therefore vertical, 
inclining it a little in a given direction, would make any given part of the crystal 
point to the magnetic poles. 
2477- A group of bismuth crystals, the apex of which was terminated by a single 
small cleavage facet, was found to give the same results. 
2478. Occasionally groups of crystals (2457.) occurred which did not seem capable 
of being placed in some one position in which they lost all directive power, but 
seemed to retain a minimum degree of force. It is very unlikely, however, that all 
the groups should be perfectly symmetric in the arrangement of their parts. It is 
more surprising that they should be so distinct in their action as they are. In 
reference to bismuth, and many other bodies, it is probable that magnetic force will 
