"For this matter, every where filling the space closed in by the curvature of heaven, is continually pushed, by its own weight, towards the centre of the world. Earth, it is true, as the heaviest, readily occupies this situation, and forcing its fellow-elements to retire, causes water, the second in weight, to be also second in place; so that the air, driven from the lowest, as well as the second station, holds the third place, leaving the highest region to be occupied by fire, the lightest of all."