Greek natural philosophers, who put forward the earliest atomic theory, that the material world
Book II 195 exhalation of moisture in the form of still tinier droplets can be spread out even above that highest heaven, and not be compelled to fall down by its weight.
They themselves, as a matter of fact, put forward the most subtle arguments to show that there can be no material particle, however minute, which cannot be further divided, but that all bodies can be divided ad infinitum, because every part of a body is a body, and every single body necessarily has a half of its quan tity.7 For this reason, then, ifwater, as we observe, can be broken up into so many tiny drops that it can be carried up as vapor above this air which is by nature lighter than water, why could it not stay also above that still lighter heaven in the form of even tinier droplets and even lighter vapors?
The coldness of the planet Saturn
5, 9. Some of our people also set out to refute in another way those who assert that there can be no waters above the heaven of the constellations on account of the weights of the elements; they argue from the qualities of the constellations themselves and their courses. The same people,8 you see, assert that the star which they call Saturn is the coldest of them all and takes thirty years to go through the circuit of the signs of the zodiac, just because it moves on a higher and therefore much more extensive orbit. The sun, after all, completes the same circuit in a year, and the moon in a month; the course being the shorter, so they say, the lower the orbit, so that the length of time taken corresponds to the space covered.
And so our people ask what it is that makes that star so cold, since it ought to be all the hotter, drawn along as it is through the loftier heaven. I mean, there can be no doubt that when a spherical mass is driven through a circular motion, its inner parts go more slowly, its outer ones faster, having to cover more ground while going through the same number ofrevolutions; and the faster they go, then of course the hotter they get. Accordingly, this aforementioned star should be hot rather than cold. For while by its own motive power it takes thirty years to travel through its whole circuit, the distance to be covered being so vast, none theless by the movement of the heaven in the opposite direction it is made to
7. Whoever these secular physicists were, they were not the heirs of Democritus, one of the early Greek natural philosophers, who put forward the earliest atomic theory, that the material world consists of indivisible particles or "atoms"; Aristotle accepted his theory. Just possibly it was rejected by the Academics, the degenerate heirs of Plato's Academy, whom the young Augustine had briefly gone along with after parting company with the Manichees. Saint Thomas, in his article on the work of the second day (Summa, 1,68,2) following Aristotle, says that no natural or physical body is infinitely divisible, but only what he calls a mathematical body. 8. Ours, or their pagan opponents? Grammatically it could be either; but from what follows in the next few paragraphs it is clear that he means the latter.