A great portion of the ground within the wall lines is not occupied by buildings, especially in the north-western quarter; and even in the more populous parts of the city, near the river, a considerable space between the houses is occupied by gardens, where pomegr a nates, figs, oranges, lemons and date-palms grow in great abundance, so that the city, when seen at a distance, has the appearance of rising out of the midst of trees.
It follows that the elements of the orbit admit of determination when the co-ordi nates of the planet at an assigned moment FIG.
The circumcircle is thus seen Areal to be a 2 yz+b 2 zx+c 2 xy=o, with centre sin 2A, sin 2B, co sin 2C; the inscribed circle is A t (x cot ZA)+ (y cot 2B) nates.