Page:A Treatise on Electricity and Magnetism - Volume 2.djvu/450

 CHAPTER XXII.

FERROMAGNETISM AND DIAMAGNETISM EXPLAINED BY MOLECULAR CURRENTS.

On Electromagnetic Theories of Magnetism.

832.] WE have seen (Art. 380) that the action of magnets on one another can be accurately represented hy the attractions and repulsions of an imaginary substance called * magnetic matter. We have shewn the reasons why we must not suppose this magnetic matter to move from one part of a magnet to another through a sensible distance, as at first sight it appears to do when we magnetize a bar, and we were led to Poisson s hypothesis that the magnetic matter is strictly confined to single molecules of the mag netic substance, so that a magnetized molecule is one in which the opposite kinds of magnetic matter are more or less separated to wards opposite poles of the molecule, but so that no part of either can ever be actually separated from the molecule (Art. 430).

These arguments completely establish the fact, that magnetiza tion is a phenomenon, not of large masses of iron, but of molecules, that is to say, of portions of the substance so small that we cannot by any mechanical method cut one of them in two, so as to obtain a north pole separate from a south pole. But the nature of a mag netic molecule is by no means determined without further investi gation. We have seen (Art. 442) that there are strong reasons for believing that the act of magnetizing iron or steel does not consist in imparting magnetization to the molecules of which it is com posed, but that these molecules are already magnetic, even in un- magnetized iron, but with their axes placed indifferently in all directions, and that the act of magnetization consists in turning the molecules so that their axes are either rendered all parallel to one direction, or at least. are deflected towards that direction.

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