Diamagnetism (Gr. sta, through, and uayvh-tns, magnetic). In the native magnet fan ore of iron) resides a peculiar force, which, if a mass of this body be suspended freely, turns or directs it into a line nearly parallel with a meridian on the earth's surface, the same end of the magnet being always directed toward the north. Certain bodies, especially iron, brought near to a magnet, have the magnetic condition induced in them, the extremity nearer either magnetic pole becoming a pole of the opposite name, that more remote a pole of the same name. Small magnetizable particles, as iron filings, dusted upon a surface on which a magnet rests, or agitated near it, become arranged in lines which, between unlike poles that are presented to each other, run across in straight lines, while about those on either side they form curves, making larger and larger sweeps into space. The lines thus indicated have been named magnetic curves, or lines of force. Until recently the number of magnetic bodies was supposed to be very small. Bec-querel in 1827 found that a needle of wood playing freely on a pivot took a direction across, not in, the magnetic curves; and in 1829 Le Bailli also observed that bismuth repelled the magnetic needle.
But the significance of these facts was not understood until Faraday in 1845, in the course of his experiments on magnetic rotary polarization, observed that a bar of so-called "heavy glass," suspended between the poles of an electro-magnet, moved, as soon as by the passage of the electrical current magnetism was induced in the latter, into a position crossing the lines of force, or at right angles to the line joining the poles. Terming the position assumed by a soft iron bar, which is lengthwise between the two poles, or from one to the other, axial, Faraday gave to the new direction assumed by the glass the name of equatorial. The glass was not merely thus directed, it was repelled by either pole; and if, reduced to the form of a small mass or cube, it was thrown out of the lines joining the poles to one side or the other, it moved into the position of weakest magnetic action. He also sealed up various liquids in long tubes of thin glass, and suspended them between the poles; some arranged themselves axially, others equatorially. This new-found property of certain bodies Faraday termed diamagnetism; and in contrast with this he denominated the familiar form of magnetic action paramagnetism.
His experiments warrant the conclusion that, with a sufficiently powerful electro-magnet, all substances whatever can be shown to exhibit one or other of these properties. (See Magnetism.)