Camera Obscura, a darkened room; or more frequently a box, admitting light by one opening, where a lens is placed; which, bringing the rays of light, from external objects, to a focus, presents a perfect picture of them, in miniature.
Capillary Tubes. Tubes, the bore of which is very small. Glass tubes are usually employed, to show the phenomenon of capillary attraction. Fluids in which they are immersed, rise in such tubes above the level of that in the containing vessel.
Centre of a Circle. A point, equally distant from every part of its circumference.
Centre of Gravity. That point within a body, to which all its particles tend, and around which they exactly balance each other. A system of bodies, as the planets, may have a common centre of gravity, around which they revolve in their orbits; whilst each, like the earth, has its particular centre of gravity within itself.
Centre of Motion. That point about which the parts of a revolving body move, which point is, itself, considered as in a state of rest.
Centre of Magnitude. The middle point of any body. Suppose a globe, one side of which is formed of lead, and the other of wood, the centres of magnitude and of gravity, would not be in the same points.
Central Forces. Those which either impel a body towards, or from, a centre of motion.
Centrifugal. That which gives a tendency to fly from a centre.
Centripetal. That which impels a body, towards a centre.
Circle. A figure; the periphery, or circumference of which, is every where equally distant, from the point, called its centre.