Page:On the connexion of the physical sciences (1834).djvu/21

Rh detached fluid mass, if at rest, would assume the form of a sphere, from the reciprocal attraction of its particles; but if the mass revolves about an axis, it becomes flattened at the poles, and bulges at the equator, in consequence of the centrifugal force arising from the velocity of rotation,—for the centrifugal force diminishes the gravity of the particles at the equator, and equilibrium can only exist where these two forces are balanced by an increase of gravity; therefore, as the attractive force is the same in all particles at equal distances from the centre of a sphere, the equatorial particles would recede from the centre, till their increase in number balanced the centrifugal force by their attraction: consequently, the sphere would become an oblate spheroid; and a fluid partially or entirely covering a solid, as the ocean and atmosphere cover the earth, must assume that form in order to remain in equilibrio. The surface of the sea is therefore spheroidal, and the surface of the earth only deviates from that figure where it rises above, or sinks below, the level of the sea; but the deviation is so small that it is unimportant when compared with the magnitude of the earth—for the mighty chain of the Andes, and the yet more lofty Himalaya, bear about the same proportion to the earth that a grain of sand does to a globe three feet in diameter. Such is the form of the earth and