The establishment of this point was
absolutely necessary to the explanation of magne-crystallic action.
With that admirable instinct which always guided him, Faraday had
seen that it was possible, if not probable, that the diamagnetic
force acts with different degrees of intensity in different
directions, through the mass of a crystal. In his studies on
electricity, he had sought an experimental reply to the question
whether crystalline bodies had not different specific inductive
capacities in different directions, but he failed to establish any
difference of the kind. His first attempt to establish differences
of diamagnetic action in different directions through bismuth, was
also a failure; but he must have felt this to be a point of cardinal
importance, for he returned to the subject in 1850, and proved that
bismuth was repelled with different degrees of force in different
directions. It seemed as if the crystal were compounded of two
diamagnetic bodies of different strengths, the substance being more
strongly repelled across the magne-crystallic axis than along it.
The same result was obtained independently, and extended to various
other bodies, magnetic as well as diamagnetic, and also to
compressed substances, a little subsequently by myself.
The law of action in relation to this point is, that in diamagnetic
crystals, the line along which the repulsion is a maximum, sets
equatorially in the magnetic field; while in magnetic crystals the
line along which the attraction is a maximum sets from pole to pole.
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