CHAP. 17. (19.)—OF THE MOTION OF THE SUN AND THE CAUSE OF THE IRREGULARITY OF THE DAYS.

The Sun himself is in four different states; twice the night is equal to the day, in the Spring and in the Autumn, when he is opposed to the centre of the earth[1], in the 8th degree of Aries and Libra[2]. 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[3]. 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.

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 æra. See the remarks of Marcus in Ajasson, ii. 246 & 373, 374.

3. The same remark applies to this as to the former observation.