Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 2.djvu/435

Book III. different ſides by turns. The vapours which ariſe from the Sun, the fixed Stars, and the tails of the Comets, may meet at laſt with, and fall into, the atmoſpheres of the Planets by their gravity; and there be condenſed and turned into water and humid ſpirits, and from thence by a flow heat paſs gradually into the form of ſalts, and ſulphurs, and tinctures, and mud, and clay, and ſand, and ſtones, and coral, and other terreſtial ſubſtances.

The hypotheſis of Vortices is preſs'd with many diffculties. That every Planet by a radius drawn to the Sun may deſcribe areas proportional to the times of deſcription, the periodic times of the ſeveral parts of the Vortices ſhould obſerve the duplicate proportion of their diſtances from the Sun. But that the periodic times of the Planets may obtain the ſeſquiplicate proportion of their diſtances from the Sun, the periodic times of the parts of the Vortex ought to be in the ſeſquiplicate proportion of their diſtances. That the ſmaller Vortices may maintain their leſſer revolutions about Saturn, Jupiter, and other Planets, and ſwim quietly and undiſurb'd in the greater Vortex of the Sun, the periodic times of the parts of the Sun's Vortex ſhould be equal. But the rotation of the Sun and Planets about their axes, which ought to correſpond with the motions of their Vortices, recede far from all theſe proportions. The motions of the Comets are exceeding regular, are govern'd by the ſame laws with the motions of the Planets, and can by no means be accounted for by the hypotheſis of Vortices. For Comets are carry'd with very eccentric motions through all parts of the heavens indifferently, with a freedom that is incompatible with the notion of a Vortex.