The Probert Encyclopaedia of Science & Technology

GRAVITATION

Gravitation is the force by reason of which all the bodies and particles of matter in the universe tend towards one another. According to the law of gravitation discovered by Isaac Newton, every portion of matter attracts every other portion with a force directly proportional to the product of the two masses, and inversely proportional to the square of the distance between them. Kepler had given the laws, deduced from observation, according to which the planets describe their orbits. From these Isaac Newton deduced the laws of the force in the case of the planets and subsequently he generalized the statement of them, by showing the identity of the nature of the force that retains the moon in her orbit, with that which attracts matter near to the surface of the earth.

The application of the grand law that he had discovered subsequently occupied a large part of the mathematical labours of Isaac Newton. Attacking the problem of lunar inequalities, he accounted for them by considering the perturbations due to the attraction of various bodies of the solar system; and by accounting for all the observed perturbations by means of his newly-discovered law he confirmed the truth of the law itself in such a way as to put it beyond all question.

The computation of these various attractions has reached such a degree of accuracy in the hands of mathematicians since Isaac Newton, that the most complicated motions of the heavenly bodies can be predicted. The law has also been applied successfully in weighing the planets, explaining the paths of comets, the motions of the tidal wave, etc. It has also been demonstrated to hold good in the case of comparatively small bodies. Thus Maskelyne determined the attraction of a particular mountain, and Cavendish and Bailly measured the attraction of balls of lead on light finely-balanced bodies, and thus determined the mean density of the earth.
Research Gravitation