he
reduced all the phenomena of magnetism to the mutual action of
electric currents.

'If we reflect upon the experiments recorded in the foregoing pages
from first to last, we can hardly fail to be convinced that
diamagnetic bodies operated on by magnetic forces possess a polarity
"the same in kind as, but the reverse in direction of, that acquired
by magnetic bodies." But if this be the case, how are we to conceive
the _physical mechanism_ of this polarity? According to Coulomb's and
Poisson's theory, the act of magnetisation consists in the
decomposition of a neutral magnetic fluid; the north pole of a magnet,
for example, possesses an attraction for the south fluid of a piece of
soft iron submitted to its influence, draws the said fluid towards it,
and with it the material particles with which the fluid is associated.
To account for diamagnetic phenomena this theory seems to fail
altogether; according to it, indeed, the oft-used phrase, "a north
pole exciting a north pole, and a south pole a south pole," involves a
contradiction. For if the north fluid be supposed to be _attracted_
towards the influencing north pole, it is absurd to suppose that its
presence there could produce _repulsion_. The theory of Ampere is
equally at a loss to explain diamagnetic action; for if we suppose the
particles of bismuth surrounded by molecular currents, then, according
to all that is known of electrodynamic laws, these currents would set
themselves parallel to, and in the same direction as, those of the
magnet, and hence attraction, and not repulsion, would be the result.
The fact, however, of this not being the case, proves that these
molecular currents are not the mechanism by which diamagnetic
induction is effected. The consciousness of this, I doubt not, drove
M. Weber to the assumption that the phenomena of diamagnetism are
produced by molecular currents, not _directed_, but actually _excited_ in
the bismuth by the magnet. Such induced currents would, according to
known laws, have a direction opposed to those of the inducing magnet,
and hence would produce the phenomena of repulsion. To carry out the
assumption here made, M. Weber is obliged to suppose that the
molecules of diamagnetic bodies are surrounded by channels, in which
the induced molecular currents, once excited, continue to flow without
resistance.' [Footnote: In assuming these non-resisting channels M.
Weber, it must be admitted, did not go beyond the assu