Even a permanent magnet is susceptible of induction, its polarity becoming thereby strengthened, weakened, or possibly reversed.
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.
The Arabic geographer, Edrisi, who lived about r roo, is said by Boucher to give an account, though in a confused manner, of the polarity of the magnet (Hallam, Mid.
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.
He also found that the polarity which minerals receive from heat has a relation to the secondary forms of their crystals - the tourmaline, for example, having its resinous pole at the summit of the crystal which has three faces.