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A LECTURE ON MAGNETISM. 379

facts without principles, or the appeal to the bodily senses
and the power of memory alone, could never inspire.

 

As an expansion of the note at page 371, the following extract may
find a place here:

“It is well known that a voltaic current exerts an attractive force
upon a second current, flowing in the same direction ; and that when the
directions are Opposed to each other the force exerted is a repulsive one.
By coiling wires into Spirals, Ampere was enabled to make them produce
all the phenomena of attraction and repulsion exhibited by magnets, and
from this it was but a step to his celebrated theory of molecular cur-
rents. He supposed the molecules of a magnetic body to be surrounded
by such currents, which, however, in the natural state of the body mu-
tually neutralized each other, on account of their confused grouping.
The act of magnetization he supposed to consist in setting these molecu-
lar currents parallel to each other ; and, starting from this principle, 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 magnetization 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 toward 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 tow-
ard 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 electro-dynamic 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

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