wheel revolves most rapidly, so the sun travels rapidly on his southern journey: he flies along his path with the velocity of wind, and traverses a great distance in a short time. In twelve Muhúrttas he passes through thirteen lunar asterisms and a half during the day; and during the night he passes through the same distance, only in eighteen Muhúrttas. As the centre of the potter's wheel revolves more slowly than the circumference, so the sun in his northern path again revolves with less rapidity, and moves over a less space of the earth in a longer time, until, at the end of his northern route, the day is again eighteen Muhúrttas, and the night twelve; the sun passing through half the lunar mansions by day and by night in those periods respectively. As the lump of clay on the centre of the potter's wheel moves most slowly, so the polar-star, which is in the centre of the zodiacal wheel, revolves very tardily, and ever remains in the centre, as the clay continues in the centre of the wheel of the potter.

The relative length of the day or night depends upon the greater or less velocity with which the sun revolves through the degrees between the two points of the horizon. In the solstitial period, in which his diurnal path is quickest, his nocturnal is slowest; and in that in which he moves quick by night, he travels slowly by day. The extent of his journey is in either case the same; for in the course of the day and night he passes through all the signs of the Zodiac, or six by night, and the same number by day: the length and shortness of the day are measured by the extent of the signs; and the duration of day and night by the period which the sun takes to pass through them 11. In his northern

declination the sun moves quickest by night, and slowest by day; in his southern declination the reverse is the case.