Book 3
1.70
This substance, he says, is converted into the four elements, fire, water, air, earth, of which the world itself and all that therein is are formed. Earth alone of these elements is not subject to change, the assumed cause being the peculiarity of its constituent triangles. For he thinks that in all the other elements the figures employed are homogeneous, the scalene triangle out of which they are all put together being one and the same, whereas for earth a triangle of peculiar shape is employed; the element of fire is a pyramid, of air an octahedron, of water an icosahedron, of earth a cube. Hence earth is not transmuted into the other three elements, nor these three into earth.
1.71
But the elements are not separated each into its own region of the universe, because the revolution unites their minute particles, compressing and forcing them together into the centre, at the same time as it separates the larger masses. Hence as they change their shapes, so also do they change the regions which they occupy.Cf. Plato, Tim. 58 a-c.
