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.