A BODY is that being which hath these three dimensions, breadth, depth, and length ;—or a bulk which makes a sensible resistance;—or whatsoever of its own nature possesseth a place.

Plato saith that it is neither heavy nor light in its own nature, when it exists in its own place; but being in the place where another should be, then it has an inclination by which it tends to gravity or levity.

Aristotle saith that, if we simply consider things in their own nature, the earth only is to be judged heavy, and fire light; but air and water are sometimes heavy and sometimes light.

The Stoics think that of the four elements two are light, fire and air; two ponderous, earth and water; that which is naturally light doth by its own nature, not by any inclination, recede from its own centre; but that which is heavy doth by its own nature tend to its centre; for the centre is not a heavy thing of itself.

Epicurus thinks that bodies are not to be limited; but the first bodies, which are simple bodies, and all those composed of them, all acknowledge gravity; that all atoms are moved, some perpendicularly, some obliquely; some are carried aloft either by direct impulse or with vibrations.