Sphere

(sfer.) [Gr. sphaira.) (Geom.) A solid body, such as would be formed by the revolution of a circle about its diameter, as an axis. Its surface is in every part equally distant from a point called its centre. Its area is equal to the perimeter of its great circle, multiplied by its diameter; and its solid contents are equal to its surface multiplied by one-third of its radius.(Ast.) The concave orb or expanse which invests our globe, and in which the heavenly bodies appear to be fixed, at an equal distance from the eye. The ancients called the orbits of the different planets, and the space occupied by the fixed stars, S.; thus, the S. ofJupiter, the S. of the fixed stars, . In the Ptolemaic astronomy, the S. were supposed to be solid and transparent; to revolve about a common centre independently of one another, each carrying its planet, ., along with it.-(Geog.) A representation of the earth on the surface of a globe; showing the position of the equator, ecliptic, meridian, . When the poles are in the horizon, the ancients called it a right S.; when in the zenith, a parallel S.; and when in any other position, an oblique S. [s. 845]