VIII. THE CONSERVATION OF ENERGY As we have seen, it was in 1831
that Faraday opened up the field of magneto-electricity.
Reversing the experiments of his predecessors, who had found
that electric currents may generate magnetism, he showed that
magnets have power under certain circumstances to generate
electricity; he proved, indeed, the interconvertibility of
electricity and magnetism. Then he showed that all bodies are
more or less subject to the influence of magnetism, and that
even light may be affected by magnetism as to its phenomena of
polarization. He satisfied himself completely of the true
identity of all the various forms of electricity, and of the
convertibility of electricity and chemical action. Thus he
linked together light, chemical affinity, magnetism, and
electricity. And, moreover, he knew full well that no one of
these can be produced in indefinite supply from another.
"Nowhere," he says, "is there a pure creation or production of
power without a corresponding exhaustion of something to su