Circle, Great. On the globe, or earth, is one that divides it into two equal parts, or hemispheres. The equator, and meridian lines, are great circles.
Circle, Lesser. Those which divide the globe into unequal parts. The tropical, arctic and antarctic circles, and all parallels of latitude, are lesser circles.
Circumference. The boundary line of any surface, as that which surrounds the centre of a circle; the four sides of a square, &c.
Comets. Bodies which revolve round the sun, in very long ovals, approaching him very nearly in their perihelion, but in their aphelion, passing to a distance immeasurably great.
Cohesion. See [Attraction].
Compressible. Capable of being forced into a smaller space.
Concave. Hollowed out; the inner surface of a watch-glass is concave, and may represent the form of a concave mirror, or lens.
Convex. Projecting, or bulging out, as the exterior surface of a watch-glass, which may represent the form of a convex mirror, or lens.
Cone. A body somewhat resembling a sugar-loaf; that is, having a round base, and sloping at the sides, until it terminates in a point.
Conjunction. When three of the heavenly bodies are in a straight or right line, if you take either of the extreme bodies, the other two are in conjunction with it; because a straight line drawn from it, might pass through the centres of both, and join them together. At the time of new moon, the moon and sun are in conjunction with the earth; and the moon and earth, are in conjunction with the sun.