Even a permanent magnet is susceptible of induction, its polarity becoming thereby strengthened, weakened, or possibly reversed.
A small permanent magnet is always liable to become demagnetized, or have its polarity reversed by the action of lightning.
The first part of the epistle deals generally with magnetic attractions and repulsions, with the polarity of the stone, and with the supposed influence of the poles of the heavens upon the poles of the stone.
Tyndall's first original work in physical science was in his experiments with regard to magnetism and diamagnetic polarity, on which he was chiefly occupied from 1850 to 1855.
(25) Unless the path of the induction is entirely inside the metal, free magnetic poles are developed at those parts of the metal where induction enters and leaves, the polarity being south at the entry and north at the exit of the flux.