GRAVITATION
, the exercise of gravity, or the pressure a body exerts on another body beneath it by the power of gravity.
This is sometimes distinguished from gravity. Thus M. Maupertuis, in his Figure de la Terre, takes gravity for that force by which a body would fall to the earth supposed at rest; and Gravitation for the same, but diminished by the centrifugal force. It is only Gravitation, or gravity thus blended with the centrifugal force, that we can usually measure by our experiments. Methods however have been found to distinguish what remains of the primitive gravity, and what has been destroyed by the centrifugal force.
It is one of the laws of nature, discovered by Newton, and now received by all philosophers, that every particle of matter in nature gravitates towards every other particle; which law is the main principle in the Newtonian philosophy. But what is called Gravitation with respect to the gravitating body, is usually called attraction with respect to the body gravitated to. The planets, both primary and secondary, as also the comets, do all gravitate towards the sun, and towards each other; as well as the sun towards them; and that in proportion to the quantity of matter in each of them.
The Peripatetics &c hold, that bodies only gravitate or weigh when out of their natural places, and that Gravitation ceases when they are restored to the same, the purpose of nature being then fulfilled: and they maintain that the final cause of this faculty is only to bring elementary bodies to their proper place, where they may rest. But the moderns shew that bodies exercise gravity even when at rest, and in their proper places. This is particularly shewn of sluids; and it is one of the laws of hydrostatics, demonstrated by Boyle and others, that fluids gravitate in proprio loco, the upper parts pressing on the lower, &c.
For the laws of Gravitation of bodies in fluids specifically lighter or heavier than themselves, see SPECIFIC Gravity. Also for the centre or line or plane of Gravitation, see Centre, Line, or Plane.
