MAGNECRYSTALLIC CONDITION OF SULPHATE OF IRON. 
41 
is always on the same side of the axial line ; and that the crystal will not stand with 
the like obliquity of 30° on the opposite side of the magnetic axis. 
2635. If the crystal be turned 180° round a vertical axis, or end for end, then the 
inclination, and the direction in which it occurs, remain unchanged ; in fact, it is 
simply giving the crystal the diametral position. But if the crystal be revolved 180° 
round a horizontal axis ; either that coinciding with its length, which represents its 
maximum magnetic direction ; or that corresponding with its breadth, and therefore 
with the magnecrystallic axis ; then the inclination is the same in amount as before, 
but it is on the other side of the axial line. 
2636. This is the case with all the prismatic crystals of sulphate of iron which I 
have tried. The elFect is very determinate ; and, as would be expected, when two 
crystals correspond in the direction of the inclination, they also correspond in the 
position of their form and direction of the various planes. 
2637. All these variations of position indicate an oblique resultant of setting force, 
derived from the joint action of the magnetic and magnecrystallic forces ; and would 
be explained by tlie supposition, that the magnecrystallic axis or line of maximum 
magnecrystallic force, was not perpendicular to the chief planes of the crystal (or 
those terminating it), but a little inclined in the direction of the length. 
2638. Whether this be the case, or whether the maximum line of magnetic force 
may not, even, be a little inclined to the length of the prism ; still, the n distance 
supplies an excellent experimental opportunity of examining this inclination, however 
small its quantity may be ; because of the facility with which the influence of either 
the one or the other may be made predominant in any required degree. 
Royal Institution, 
December 5, 1848. 
2639. IVofe. (2591.) Another supposition may be thrown out for consideration. I 
have already said that the assumption of a mere axial condition (2587.2591.) would 
account for the set without attraction or repulsion. Now if we suppose it possible 
that the molecules should become polar in relation to the north and south poles of 
the magnet, but with no mutual relation amongst themselves, then the bismuth or 
other crystal might set as if induced with mere axial power : but it seems to me very 
improbable that polarities of a given particle in a crystal should be subject to the in- 
fluence of the polarities of the distant magnet poles, and not also to the like polarities 
of the contiguous particles. — January 24, 1849. 
MDCCCXLIX. 
G 
