Thales, Pythagoras, and the followers of Pythagoras do distribute the universal globe of heaven into five circles which they denominate zones; one of which is called the arctic circle, which is always conspicuous to us, another is the summer tropic, another is the equinoctial, another is the winter tropic, another is the antarctic circle, which is always invisible. The circle called the zodiac is placed under the three that are in the midst, and lies obliquely, gently touching them all. Likewise, they are all cut in right angles by the meridian, which runs from pole to pole. It is supposed that Pythagoras made the first discovery of the obliquity of the zodiac, but one Oenopides of Chios challenges to himself the invention of it. CHAPTER XIII. WHAT IS THE ESSENCE OF THE STARS, AND HOW THEY ARE COMPOSED. Thales believes that they are globes of earth set on fire. Empedocles, that they are fiery bodies arising from that fire which the ether embraced within itself, and did shatter in pieces when the elements were first separated one from another. Anaxagoras, that the circumambient ether is of a fiery substance, which, by a vehement force in its whirling about, did tear stones from the earth, and by its own power set them on fire, and establish them as stars in the heavens. Diogenes thinks they resemble pumice stones, and that they are the breathings of the world; again he supposeth that there are some invisible stones, which sometimes fall from heaven upon the earth, and are there quenched; as it happened at Aegos-potami, where a stony star resembling fire did fall. Empedocles, that the fixed stars are fastened to the crystal, but the planets are loosened. Plato, that the stars for the most part are of a fiery nature, but they are made partakers of another element, with which they are mixed after the resemblance of glue. Xenophanes, that they are composed of inflamed clouds, which in the daytime are quenched, and in the night are kindled again. The like we see in coals; for the rising and setting of the stars is nothing else but the quenching and kindling of them. Heraclides and the Pythagoreans, that every star is a world in an infinite ether, and itself encompasseth air, earth, and ether; this opinion is current among the followers of Orpheus, for they suppose that each of the stars does make a world. Epicurus condemns none of these opinions, for he embraces any thing that is possible. CHAPTER XIV. OF WHAT FIGURE THE STARS ARE. The Stoics say that the stars are of a circular form, like the sun, the moon, and the world. Cleanthes, that they are of a conical figure. Anaximenes, that they are fastened as nails in the crystalline firmament; some others, that they are fiery plates of gold, resembling pictures. CHAPTER XV. OF THE ORDER AND PLACE OF THE STARS.