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