8 “And God called the firmament heaven.” The nature of right belongs to another, and the firmament only shares it on account of its resemblance to heaven. We often find the visible region called heaven, on account of the density and continuity of the air within our ken, and deriving its name “heaven” from the word which means to see. It is of it that Scripture says, “The fowl of the air,” “Fowl that may fly...in the open firmament of heaven;” and, elsewhere, “They mount up to heaven.” Moses, blessing the tribe of Joseph, desires for it the fruits and the dews of heaven, of the suns of summer and the conjunctions of the moon, and blessings from the tops of the mountains and from the everlasting hills, in one word, from all which fertilises the earth. In the curses on Israel it is said, “And your heaven that is over your head shall be brass.” What does this mean? It threatens him with a complete drought, with an absence of the aerial waters which cause the fruits of the earth to be brought forth and to grow.
Since, then, Scripture says that the dew or the rain falls from heaven, we understand that it is from those waters which have been ordered to occupy the higher regions. When the exhalations from the earth, gathered together in the heights of the air, are condensed under the pressure of the wind, this aerial moisture diffuses itself in vaporous and light clouds; then mingling again, it forms drops which fall, dragged down by their own weight; and this is the origin of rain. When water beaten by the violence of the wind, changes into foam, and passing through excessive cold quite freezes, it breaks the cloud, and falls as snow. You can thus account for all the moist substances that the air suspends over our heads.
And do not let any one compare with the inquisitive discussions of philosophers upon the heavens, the simple and inartificial character of the utterances of the Spirit; as the beauty of chaste women surpasses that of a harlot, so our arguments are superior to those of our opponents. They only seek to persuade by forced reasoning. With us truth presents itself naked and without artifice. But why torment ourselves to refute the errors of philosophers, when it is sufficient to produce their mutually contradictory books, and, as quiet spectators, to watch the war? For those thinkers are not less numerous, nor less celebrated, nor more sober in speech in fighting their adversaries, who say that the universe is being consumed by fire, and that from the seeds which remain in the ashes of the burnt world all is being brought to life again. Hence in the world there is destruction and palingenesis to infinity. All, equally far from the truth, find each on their side by-ways which lead them to error.
Source: Nine Homilies of Hexaemeron (New Advent)