ested Faraday so much. Drawn by
the fame of Bunsen as a teacher, in the year 1848 I became a student in
the University of Marburg, in Hesse Cassel. Bunsen's behaviour to me
was that of a brother as well as that of a teacher, and it was also my
happiness to make the acquaintance and gain the friendship of Professor
Knoblauch, so highly distinguished by his researches on Radiant Heat.
Plucker's and Faraday's investigations filled all minds at the time,
and towards the end of 1849, Professor Knoblauch and myself commenced
a joint investigation of the entire question. Long discipline was
necessary to give us due mastery over it. Employing a method proposed by
Dove, we examined the optical properties of our crystals ourselves;
and these optical observations went hand in hand with our magnetic
experiments. The number of these experiments was very great, but for
a considerable time no fact of importance was added to those already
published. At length, however, it was our fortune to meet with various
crystals whose deportment could not be brought under the laws of
magne-crystallic action enunciated by Plucker. We also discovered
instances which led us to suppose that the magne-crystallic force was
by no means independent, as alleged, of the magnetism or diamagnetism of
the mass of the crystal. Indeed, the more we worked at the subject, the
more clearly did it appear to us that the deportment of crystals in the
magnetic field was due, not to a force previously unknown, but to
the modification of the known forces of magnetism and diamagnetism by
crystalline aggregation.

An eminent example of magne-crystallic action adduced by Plucker, and
experimented on by Faraday, was Iceland spar. It is what in optics is
called a negative crystal, and according to the law of Plucker, the axis
of such a crystal was always repelled by a magnet. But we showed that it
was only necessary to substitute, in whole or in part, carbonate of iron
for carbonate of lime, thus changing the magnetic but not the optical
character of the crystal, to cause the axis to be attracted. That the
deportment of magnetic crystals is exactly antithetical to that of
diamagnetic crystals isomorphous with the magnetic ones, was proved
to be a general law of action. In all cases, the line which in
a diamagnetic crystal set equatorially, always set itself in an
isomorphous magnetic crystal axially. By mechanical compression other
bodies were also made to imitate the Iceland