POLARITY

, the quality of a thing having poles, or pointing to, or respecting some pole: as the magnetic needle, &c.

By heating an iron bar, and letting it cool again in a vertical position, it acquires a polarity, or magnetic virtue: the lower end becoming the north pole, and the upper end the south pole. But iron bars acquire a polarity by barely continuing a long time in an erect position, even without heating them. Thus, the upright iron bars of some windows, &c, are often sound to have poles: Nay, an iron rod acquires a polarity, by the mere holding it erect; the lower end, in that case, attracting the south end of a magnetic needle; and the upper, the north end. But these poles are mutable, and shift with the situation of the rod.

Some modern writers, particularly Dr. Higgins, in his Philosophical Essay concerning Light, have maintained the polarity of the parts of matter, or that their simple attractions are more forcible in one direction, or axis of each atom, than in any other.