Page:The Natural History of Pliny.djvu/85

Chap. 18.] ACCOUNT OF THE WORLD.

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 night is then twice changed, when the day increases in length, from the winter solstice in the 8th degree of Capricorn, and afterwards, when the 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 THUNDER IS ASCRIBED TO JUPITER.

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 off this celestial fire, bearing the omens of future events, even the part which is

^ 1 "centrum terræ;" the equator, the part equally distant from the two poles or extremities. ^ 2 It may be remarked, that the equinoxes did not actually take place at this period in the points mentioned by Pliny, but in the 28th degrees of Pisces and Virgo respectively ; he appears to have conformed to the popular opinion, as we may learn from Columella, lib. ix. cap. 14. The degrees mentioned above were those fixed by the Greek astronomers who formed the celestial sphere, and which was about 138 years before the Christian era. See the remarks of Marcus in Ajasson, ii. 246 & 373, 374. ^ 3 The same remark applies to this as to the former observation. ^ 4 "siderum." ^ 5 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.