Page:The Natural History of Pliny.djvu/85

 Chap. 18.] ACCOTJNT OF THE WOELD. 51 is equal to the day, in the Spring and in the Autumn, when he is opposed to the centre of the earth in the 8th degree of Aries and Libra^. The length of the day and the niglit is then twice changed, when the day increases in length, from the winter solstice in the 8th degree of Capricorn, and afterwards, when tlie night increases in length from the summer solstice in the 8th degree of Cancer^. The cause of this inequality is the obliquity of the zodiac, since there is, at every moment of time, an equal portion of the firmament above and below the horizon. But the signs which mount directly upwards, when they rise, retain the light for a longer space, while those that are more oblique pass along more quickly. CHAP. 18. (20.) — WHY THTJJiTDEE IS ASCEIBED TO JXJPITEE. It is not generally known, what has been discovered by men who are the most eminent for their learning, in con- sequence of their assiduous observations of the heavens, that the fires which fall upon the earth, and receive the name of thunder-bolts, proceed from the three superior stars'*, but principally from the one which is situated in the middle. It may perhaps depend on the superabundance of moisture from the superior orbit communicating with the heat from the inferior, which are expelled in this manner^ ; and hence it is commonly said, the thunder-bolts are darted by Jupiter. And as, in burning wood, the burnt part is cast off" with a crackling noise, so does the star throw ofi" this celestial fire, bearing the omens of future events, even the part which is ^ " centrum ten'se ; " the equator, the part equally distant from the two poles or extremities. ^ It may be remarked, that the equinoxes did not actually take place at this period in the pomts mentioned by Phny, but in the 28th deojrees of Pisces and Yirgo respectively ; he appears to have conformed to the popular opinion, as we may learn from Columella, Hb. ix. cap. 14. The degrees mentioned above were those fixed by the Greek astronomers who formed the celestial sphere, and which Avas about 138 years before the Christian ara. See the remarks of Marcus in Ajasson, ii. 246 & 373, 374. 3 The same remark apphes to this as to the former observation. ° The hypothesis of the author is, that the excess of moisture in the orbit of Saturn, and the excess of heat in that of Mars, unite in the orbit of Jupiter and are discharged in the form of thunder. e2
 * " siderum."