Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/238

 this investigation, when suspended between the poles of an electro-magnet, set itself across the line joining the poles: thus behaving in the contrary way to a bar of an ordinary magnetic substance, which would tend to set itself along this line. A simpler manifestation of the effect was obtained when a cube or sphere of the substance was used; in such forms it showed a disposition to move from the stronger to the weaker places of the magnetic field. The pointing of the bar was then seen to be merely the resultant of the tendencies of each of its particles to move outwards into the positions of weakest magnetic action.

Many other bodies besides heavy glass were found to display the same property; in particular, bismuth. The name diamagnetic was given to them.

"Theoretically," remarked Faraday, "an explanation of the movements of the diamagnetic bodies might be offered in the supposition that magnetic induction caused in them a contrary state to that which it produced in magnetic matter; i.e. that if a particle of each kind of matter were placed in the magnetic field, both would become magnetic, and each would have its axis parallel to the resultant of magnetic force passing through it; but the particle of magnetic matter would have its north and south poles opposite, or facing toward the contrary poles of the inducing magnet, whereas with the diamagnetic particles the reverse would be the case; and hence would result approximation in the one substance, recession in the other. Upon Ampère's theory, this view would be equivalent to the supposition that, as currents are induced in iron and magnetics parallel to those existing in the inducing magnet or battery wire, so in bismuth, heavy glass, and diamagnetic bodies, the currents induced are in the contrary direction."

This explanation became generally known as the "hypothesis of diamagnetic polarity"; it represents diamagnetism as similar