CIRCLES of the Sphere

CIRCLES of the Sphere, are such as cut the mundane sphere, and have their periphery either on its moveable surface, or in another immovable, conterminous, and equidistant surface. See SPHERE. Hence arise two kinds of circles, moveable and immoveable. The first, those whose peripheries are in the moveable surface, and which therefore revolve with its diurnal mo-

tion; as, the meridians, &c. The latter having their periphery in the immovable surface, do not revolve; as the ecliptic, equator, and its parallels, &c. See GEOGRAPHY.