Editorial note — Book II.

[The remaining two books of the treatise known by the title ‘De Cœlo,’ while connected with the foregoing, are still more closely connected with the two Books composing the treatise entitled ‘De Generatione et Corruptione.’ The discussion carried on throughout the two treatises is in truth one; but, if anywhere broken, it is at the end of Book II. De Cœlo, as above. From this point Aristotle proceeds to consider (in four Books) the particular phenomena presented by natural bodies — phenomena of Generation and Destruction (in the widest sense of these words) — dependent on the opposition of the upward and downward motions; bodies, thus light or heavy, being thence seen to be ultimately reducible to four elements variously combined. Treating of the Kosmos in its larger aspects, the first two Books of De Cœlo, here abstracted, are obviously those that alone correspond strictly to the name of the treatise.]