Attraction

Collier's New Encyclopedia (1921)

in natural philosophy, a force in virtue of which the material particles of all bodies tend necessarily to approach each other. It operates at whatever distances the bodies may be from each other, whether the space between them be filled with other masses of matter or is vacant, and whether the bodies themselves are at rest or are in motion. When they are not closely in contact, the attraction between them is called that of gravitation or of gravity. It is of various kinds: (1) The attraction of gravitation or of gravity is the operation of the above-mentioned ned attraction when the bodies acting and acted upon are not closely in contact. It is often called the law of gravity or gravitation, but the term law in this case means simply generalization. It states the universality of a fact, but does not really account for it. By this law or generalization, the attraction between any two material particles is directly proportional to the product of their masses, and inversely proportional to the square of their distance asunder. (2) Molecular attraction differs from the former in acting only at infinitely small distances. It ceases to be appreciable when the distances between the molecules become appreciably large. It is divided into cohesion, affinity, and adhesion. Capillary attraction, meaning the attraction excited by a hair-like tube on a liquid within it, is, properly speaking, a variety of adhesion. In magnetism, the power excited by a magnet or loadstone of drawing and attaching iron to itself. In electricity, the power possessed by an body drawing certain other bodies to itself. The repulsions or attractions between two electrified bodies are in the inverse ratio of the squares of their distance. The distance remaining the same, the force of attraction or repulsion between two electrified bodies is directly as the product of the quantities of electricity with which they are charged.