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. (25.) The Greeks name these stars _comets_[271]; we name them Crinitæ, as if shaggy with bloody locks, and surrounded with bristles like hair. Those stars, which have a mane hanging down from their lower part, like a long beard, are named Pogoniæ[272]. Those that are named Acontiæ[273] 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. When they are short and pointed they are named Xiphiæ[274]; these are the pale kind; they shine like a sword and are without any rays; while we name those Discei[275], which, being of an amber colour, in conformity with their name, emit a few rays from their margin only. A kind named Pitheus[276] exhibits the figure of a cask, appearing convex and emitting a smoky light. The kind named Cerastias[277] has the appearance of a horn; it is like the one which was visible when the Greeks fought at Salamis. Lampadias[278] is like a burning torch; Hippias[279] is like a horse’s mane; it 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[280]. The shortest time during which any one of them has been observed to be visible is 7 days, the longest 180 days. CHAP. 23.—THEIR NATURE, SITUATION, AND SPECIES.