Faraday, Michael, 1791-1867; Physicists -- Great Britain -- Biography
Faraday's thoughts ran intuitively into experimental combinations,
so that subjects whose capacity for experimental treatment would, to
ordinary minds, seem to be exhausted in a moment, were shown by him to
be all but inexhaustible. He has now an object in view, the first step
towards which is the proof that the principle of Archimedes is true of
magnetism. He forms magnetic solutions of various degrees of strength,
places them between the poles of his magnet, and suspends in the
solutions various magnetic bodies. He proves that when the solution
is stronger than the body plunged in it, the body, though magnetic,
is repelled; and when an elongated piece of it is surrounded by the
solution, it sets, like a diamagnetic body, equatorially between the
excited poles. The same body when suspended in a solution of weaker
magnetic power than itself, is attracted as a whole, while an elongated
portion of it sets axially.
And now theoretic questions rush in upon him. Is this new force a true
repulsion, or is it merely a differential attraction? Might not the
apparent repulsion of diamagnetic bodies be really due to the greater
attraction of the medium by which they are surrounded? He tries the
rarefaction of air, but finds the effect insensible. He is averse to
ascribing a capacity of attraction to space, or to any hypothetical
medium supposed to fill space. He therefore inclines, but still with
caution, to the opinion that the action of a magnet upon bismuth is a
true and absolute repulsion, and not merely the result of differential
attraction. And then he clearly states a theoretic view sufficient to
account for the phenomena. 'Theoretically,' he says, 'an explanation of
the movements of the diamagnetic bodies, and all the dynamic phenomena
consequent upon the action of magnets upon them, might be offered in the
supposition that magnetic induction caused in them a contrary state to
that which it produced in ordinary matter.' That is to say, while in
ordinary magnetic influence the exciting pole excites adjacent to itself
the contrary magnetism, in diamagnetic bodies the adjacent magnetism is
the same as that of the exciting pole. This theory of reversed polarity,
however, does not appear to have ever laid deep hold of Faraday's mind;
and his own experiments failed to give any evidence of its truth. He
therefore subsequently abandoned it, and maintained the non-polarity of
the diamagnetic force.
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