Further, some have thought that the heaven encircles the universe and has the form of a sphere, and that everywhere it is the highest point, and that the centre of the space enclosed by it is the lowest part: and, further, that those bodies that are light and airy are allotted by the Creator the upper region: while those that are heavy and tend to descend occupy the lower region, which is the middle. The element, then, that is lightest and most inclined to soar upwards is fire, and hence they hold that its position is immediately after the heaven, and they call it ether, and after it comes the lower air. But earth and water, which are heavier and have more of a downward tendency, are suspended in the centre. Therefore, taking them in the reverse order, we have in the lowest situation earth and water: but water is lighter than earth, and hence is more easily set in motion: above these on all hands, like a covering, is the circle of air, and all round the air is the circle of ether, and outside air is the circle of the heaven.