FRICTION, the act of rubbing or grating the surface of one body against that of another, called also attrition. The phenomena arising upon the friction of divers bodies, under different circumstances, are very numerous and considerable. Mr Hawksee gives us a number of experiments of this kind; particularly of the attrition or friction of glass, under various circumstances, the result of which was, that it yielded light and became electrical. All bodies by friction produce heat; many of them emit light; particularly a cat's back, sugar, beaten sulphur, mercury, sea water, gold, copper, &c. but, above all, diamonds, which, when briskly rubbed against glass, gold, or the like, yield a light equal to that of a live coal when blown by the bellows. See ELECTRICS and ELECTRICITY.