Text: At one time Faraday thought that diamagnetic repulsion could be explained on the supposition that there existed a "diamagnetic polarity" the reverse of the ordinary magnetic polarity. According to this view, which, however, Faraday himself quite abandoned, a magnet, when its N pole is presented to the end of a bar of bismuth, induces in that end a N pole (the reverse of what it would induce in a bar of iron or other magnettic metal), and therefore repels it. Weber adopted this view, and Tyndall warmly advocated it, especially after discovering that the repelling diamagnetic force varies as the square of the magnetic power employed. It has been even suggested that when a diamagnetic bar lies equatorially across a field of force, its east and west poles possess different properties. The experiments named above suggest, however, an explanation less difficult to reconcile with the facts. It has been pointed out that the degree to which magnetization goes on in a medium depends upon the magnetic permeability of that medium. Now, permeability expresses the number of magnetic lines induced in the medium for every line of magnetizing force applied. A certain magnetizing force applied to a space containing air or vacuum would induce a certain number of magnetic lines through it. If the space considered were occupied by a paramagnetic substance it would concentrate the magnetic lines into itself, as a sphere does. But if the sphere were of a permeability less than 1, the magnetic lines would tend rather to pass through the air. If the space considered were occupied by bismuth, the same magnetizing force would induce in the bismuth fewer magnetic lines than in a vacuum. But those lines which were induced would still run in the same general direction as in the vacuum; not in the opposite direction, as Weber and Tyndall maintained. The result of there being a less induction through diamagnetic substances can be shown to be that such substances will be urged from places where the magnetic force is strong to places where it is weaker. This is why a ball of bismuth moves away from a magnet, and why a little bar of bismuth between the conical poles of the electromagnet turns equatorially so as to put its ends into the regions that are magnetically weaker. There is no reason to doubt that in a magnetic field of uniform strength a bar of bismuth would point along the lines of induction.

See Also: PARAMAGNETISM; OXYGEN

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