These stars occur both at sea and at land. 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[317]. 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[318], 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. CHAP. 38. (38.)—OF THE AIR AND ON THE CAUSE OF THE SHOWERS OF STONES. So far I have spoken of the world itself and of the stars. I must now give an account of the other remarkable phænomena of the heavens. For our ancestors have given the name of heavens, or, sometimes, another name, air, to all the seemingly void space, which diffuses around us this vital spirit. It is situated beneath the moon, indeed much lower, as is admitted by every one who has made observations on it, and is composed of a great quantity of air from the upper regions, mixed with a great quantity of terrestrial vapour, the two forming a compound. Hence proceed clouds, thunder and lightning of all kinds; hence also hail, frost, showers, storms and whirlwinds; hence proceed many of the evils incident to mortals, and the mutual contests of the various parts of nature. The force of the stars keeps down all terrestrial things which tend towards the heavens, and the same force attracts to itself those things which do not go there spontaneously. The showers fall, mists rise up, rivers are dried up, hail-storms rush down, the rays of the sun parch the earth, and impel it from all quarters towards the centre. The same rays, still unbroken, dart back again, and carry with them whatever they can take up. Vapour falls from on high and returns again to the same place. Winds arise which contain nothing, but which return loaded with spoils. The breathing of so many animals draws down the spirit from the higher regions; but this tends to go in a contrary direction, and the earth pours out its spirit into the void space of the heavens. Thus nature moving to and fro, as if impelled by some machine[319], discord is kindled by the rapid motion of the world. Nor is the contest allowed to cease, for she is continually whirled round and lays open the causes of all things, forming an immense globe about the earth, while she again, from time to time, covers this other firmament with clouds[320].