is a solid contained under one uniform round surface, every point of which is equally distant from a certain point in the middle called its centre; and is formed by the revolution of a semicircle about its diameter. See Geometry.

Projection of the Sphere. See Projection.

Astronomy, that concave orb or expanse which invests our globe, and in which the heavenly bodies appear to be fixed, and at an equal distance from the eye.

The better to determine the places of the heavenly bodies in the sphere, several circles are supposed to be described on the surface thereof, hence called the circles of the sphere: of these some are called great circles, as the equinoctial, ecliptic, meridian, &c. and others small circles, as the tropics, parallels, &c. See Geography; and Astronomy, paffim.

Armillary Sphere. See Geography.

Sphere of Activity of a Body, is that determinate space or extent to which, and no farther, the effluvia continually emitted from that body reach; and where they operate according to their nature.