The stadium is equal to one hundred and twenty-five of our Roman paces, or six hundred and twenty-five feet. Posidonius supposes that there is a space of not less than forty stadia around the earth, whence mists, winds and clouds proceed; beyond this he supposes that the air is pure and liquid, consisting of uninterrupted light; from the clouded region to the moon there is a space of two million of stadia, and thence to the sun of five hundred million. It is in consequence of this space that the sun, notwithstanding his immense magnitude, does not burn the earth. Many persons have imagined that the clouds rise to the height of nine hundred stadia. These points are not completely made out, and are difficult to explain; but we have given the best account of them that has been published.
CHAPTER IV.
OF THE STARS WHICH APPEAR SUDDENLY, OR OF COMETS.
A few things still remain to be said concerning the world; for stars are suddenly formed in the heavens themselves; of these there are various kinds.
The Greeks name these stars comets, we name them Crinitæ, as if shaggy with bloody locks, and surrounded with bristles like hair. Some of them have a mane hanging down from their lower part, like a long beard, some vibrate like a dart with a very quick motion. It was one of this kind which the Emperor Titus described in his very excellent poem, as having been seen in his fifth consulship; and this was the last of these bodies which has been observed. Some are short and pointed, of a pale color, and shine like a sword without any rays; others of an amber color emit a few rays from their margin only. One kind exhibits the figure of a cask, appearing convex and emitting a smoky light; another has the appearance of a horn; it is like the one which was visible when the Greeks fought at Salamis. Occasionally you see one like a burning torch; and again one like a horse’s mane; the latter often has a very rapid motion, like a circle revolving on itself. There is also a white comet, with silver hair, so brilliant that it can scarcely be looked at, exhibiting, as it were, the aspect of the Deity in a human form. There are some also that are shaggy, having the appearance of a fleece, surrounded by a kind of crown. There was one, where the appearance of a mane was changed into that of a spear; it happened in the 109th olympiad, in the 398th year of the City.[16] The shortest time during which any one of them has been observed to be visible is seven days, the longest one hundred and eighty days.
Rome is the only place in the whole world where there is a temple dedicated to a comet—the one which was thought by the late Emperor Augustus to be auspicious to him, from its appearing during the games which he was celebrating in honor of Venus, not long after the death of his father Cæsar. He expressed his joy in these terms: “During the very time of these games of mine, a hairy star was seen during seven days, in the part of the heavens which is under the Great Bear. It rose about the eleventh hour of the day, was very bright, and was conspicuous in all parts of the earth. The common people supposed the star to indicate, that the soul of Cæsar was admitted among the immortal Gods.” This is what he proclaimed in public, but, in secret, he rejoiced at this auspicious omen, interpreting it as produced for himself; and, to confess the truth, it really proved a salutary omen for the world at large.
Some persons suppose that these stars are permanent and that they move through their proper orbits, but that they are only visible when they recede from the sun. Others suppose that they are produced by an accidental vapor together with the force of fire, and that, from this circumstance, they are liable to be dissipated.
CHAPTER V.
THE DOCTRINE OF HIPPARCHUS ABOUT THE STARS.
Hipparchus, who can never be sufficiently commended, as one who more especially proved the relation of the stars to man, and that our souls are a portion of heaven, discovered a new star that was produced in his own age, and, by observing its motions on the day in which it shone, he was led to doubt whether this does not often happen, that those stars have motion which we suppose to be fixed. And the same individual attempted, what might seem presumptuous even in a deity, to number the stars for posterity and to express their relations by appropriate names; having previously devised instruments,[17] by which he might mark the place and the magnitude of each individual star. In this way it might be easily discovered, not only whether they were destroyed or produced, but whether they changed their relative positions, and likewise, whether they were increased or diminished; the heavens being thus left as an inheritance to any one, who might be found competent to complete his plan.
CHAPTER VI.
OF THE STARS WHICH ARE NAMED CASTOR AND POLLUX.
I have seen, during the night-watches of the soldiers, a luminous appearance, like a star, attached to the javelins on the ramparts. They also settle on the yard-arms and other parts of ships while sailing, producing a kind of vocal sound, like that of birds flitting about. When they occur singly they are mischievous, so as even to sink the vessels, and if they strike on the lower part of the keel, setting them on fire. When there are two of them they are considered auspicious, and are thought to predict a prosperous voyage, as it is said that they drive away that dreadful and terrific meteor named Helena. On this account their efficacy is ascribed to Castor and Pollux, and they are invoked as gods. They also occasionally shine round the heads of men in the evening,[18] which is considered as predicting something very important. But there is great uncertainty respecting the cause of all these things, and they are concealed in the majesty of nature.