BOOK II. XVI. 79-xviii. 82 



afterwards radiant ; with these being causally con- 

 nected also the appearance of the fixed stars. For 

 at one time there is a dense crowd of stars in the sky 

 round the circle of the half-moon, a fine night giving 

 them a gentle radiance, but at another time they 

 are scarce, so that we wonder at their flight, when 

 the full moon hides them or when the rays of the 

 sun or the planets above-mentioned dim our sight. 

 But the moon herself also is undoubtedly sensitive 

 to the variations of the strength of impact of the 

 rays of the sun, as moreover the curve of the earth 

 dulls their impact, except when the impact of the 

 rays meets at a right angle. And so the moon is 

 at half in the sun's quadrature, and curved in a 

 hoUow circle in its trinal aspect, but waxes to full 

 at the sun's opposition, and then waning exhibits 

 the same configurations at correspouding intervals, 

 on the same principle as the three planets above 

 the sun. 



XVII. The sun itself has four differences, as there Thesun's 

 are two equinoxes, in spring and autumn, when *-^'^*^* 

 it coincides with the centre of the earth at the eighth 

 degree of Aries and Libra, and two changes of its 

 course, in the eighth degree of Capricorn at mid- 

 winter when the days begin to lengthen and in the 



same degree of Cancer at the summer solstice. The 

 variation is due to the slant of the zodiac, as at every 

 moment an equal part of the fii*mament is above and 

 below the earth ; but the planets that foUow a 

 straight path at their rising keep their light for a 

 longer tract and those that follow a slanting path 

 pass in a swifter period. 



XVIII. Most men are not acquainted with a truth Thunderboiu 

 known to the founders " of the science from their ^i^eu'^ 



225 



