Attraction.

Attraction. The mutual action between any two bodies is termed stress. When the stress tends to separate the bodies, or to prevent their mutual approach, it is termed a pressure or repulsion. When the stress is such that the bodies tend to approach each other, it is termed a tension or attraction. The words repulsion and attraction are used when the bodies are considered to influence each other directly; but when the action is considered to be propagated through an intervening medium, the terms pressure and tension are used. Newton believed that no action could be propagated except through a medium. Electric and magnetic phenomena have been very completely accounted for by the action of a medium (see ELECTRICITY). Attempts to explain gravitation by such action have not been so successful. Though they account sufficiently for the observed phenomena, they all postulate the existence of an unlimited supply of energy. Sir W. Thomson has shown that Cohesion (q.v.) can be explained by the Newtonian law of gravitational attraction. See GRAVITATION, CAPILLARITY, CHEMISTRY, MAGNETISM.