freely as we suspended our
darning-needle, and bring the other near it; what will occur? The red
component of the strip you hold in your hand will repel the red
component of your suspended strip; but then it will attract the green,
and, the forces being equal, they neutralise each other. In fact, the
least reflection shows you that the strips will be as indifferent to
each other as two unmagnetised darning-needles would be under the same
circumstances.

But suppose, instead of mixing the colours, we painted one half of
each strip from centre to end red, and the other half green, it is
perfectly manifest that the two strips would now behave towards each
other exactly as our two magnetised darning-needles--the red end would
repel the red and attract the green, the green would repel the green
and attract the red; so that, assuming two colours thus related to
each other, we could by their mixture produce the neutrality of an
unmagnetised body, while by their separation we could produce the
duality of action of magnetised bodies.

But you have already anticipated a defect in my conception; for if we
break one of our strips of wood in the middle we have one half
entirely red, and the other entirely green, and with these it would be
impossible to imitate the action of our broken magnet. How, then,
must we modify our conception? We must evidently suppose _each
molecule of the wood_ painted green on one face and red on the opposite
one. The resultant action of all the atoms would then exactly
resemble the action of a magnet. Here also, if the two opposite
colours of each atom could be caused to mix so as to produce white, we
should have, as before, perfect neutrality.

For these two self-repellent and mutually attractive colours,
substitute in your minds two invisible self-repellent and mutually
attractive fluids, which in ordinary steel are mixed to form a neutral
compound, but which the act of magnetisation separates from each
other, placing the opposite fluids on the opposite face of each
molecule. You have then a perfectly distinct conception of the
celebrated theory of magnetic fluids. The strength of the magnetism
excited is supposed to be proportional to the quantity of neutral
fluid decomposed. According to this theory nothing is actually
transferred from the exciting magnet to the excited steel. The act of
magnetisation consists in the forcible separation of two fluids which
existed in the steel before it