Note 186 — Chapter X

Those bodies which are attracted by a magnet, as iron is, are called magnetic bodies. Those which are, on the contrary, repelled by the same power, are termed diamagnetic bodies. On these Dr. Faraday remarks:—“Of the substances which compose the crust of the earth, by far the greater portion belong to the diamagnetic class; and though ferruginous and other magnetic matters, being more energetic in their action, are more striking in their phenomena, we should be hasty in assuming that, therefore, they over rule entirely the effect of the former bodies. As regards the ocean, lakes, rivers, and the atmosphere, they will exert their peculiar effect almost uninfluenced by any magnetic matter in them, and as respects the rocks and mountains, their diamagnetic influence is perhaps greater than might be anticipated. I mentioned that by adjusting water and a salt of iron together, I obtained a solution inactive in air; that is, by a due association of the forces of a body, from each class, water and a salt of iron, the magnetic force of the latter was entirely counteracted by the diamagnetic force of the former, and the mixture was neither attracted nor repelled: To produce this effect, it required that more than 48·6 grains of crystallised protosulphate of iron should be added to ten cubic inches of water (for these proportions gave a solution which would set equatorially), a quantity so large, that I was greatly astonished on observing the power of the water to overcome it. It is not, therefore, at all unlikely that many of the masses which form the crust of this our globe, may have an excess of diamagnetic power, and act accordingly.”—On new magnetic actions, and on the magnetic condition of all matter; by Michael Faraday, D.C.L., F.R.S., &c.—Philosophical Transactions, Jan. 1846, vol. cxxxvii. p. 41.