We find also, that Attrition, if it be any thing vehement, is wont to produce Heat in the solidest bodies; as when the blade of a Knife being nimbly whetted grows presently hot. And if having taken a brass Nail, and driven it as far as you can to the end of the stick, to keep it fast and gain a handle, you then strongly rub the head to and fro against the floor or a plank of wood, you may quickly find it to have acquired a Heat intense enough to offend, if not burn ones fingers. And I remember, that going once in exceeding hot weather in a Coach, which for certain reasons we caus'd to be driven very fast, the attrition of the Nave of the Wheel against the Axel-tree was so vehement as oblig'd us to light out of the Coach to seek for water, to cool the over-chased parts, and stop the growing mischief the excessive Heat had begun to do.
The vulgar Experiment of strikeing fire with a Flint and Steel sufficiently declares, what a heat in a tricemay
