CIPHERING. A term in carpentry. (_See_ SYPHERED.)
CIRCLE. A plane figure bounded by a line called the circumference, everywhere equally distant from a point within it, called the centre.
CIRCLE OF PERPETUAL APPARITION. A circle of the heavens parallel to the equator, and at a distance from the pole of any place equal to the latitude: within this circle the stars never set.
CIRCLES, GREAT, LESSER, AZIMUTH, VERTICAL (which see).
CIRCLES OF LONGITUDE. These are great circles passing through the poles of the ecliptic, and so cutting it at right angles.
CIRCULARS. Certain official letters which are sent to several persons, and convey the same information.
CIRCUMNAVIGATION. The term for making a voyage round the world.
CIRCUMPOLAR. A region which includes that portion of the starry sphere which remains constantly above the horizon of any place.
CIRCUMVALLATION, LINES OF. Intrenchments thrown up by a besieging army, outside itself, and round the besieged place, but fronting towards the country, to prevent interference from outside. This continuous method has gone out of favour, though some covering works of concentrated strength are still considered essential.
CIRRIPEDIA. A group of marine animals, allied to the crustacea. They are free and natatory when young, but in the adult state attached to rocks or some floating substance. They are protected by a multivalve shell, and have long ciliated curled tentacles, whence their name (_curl-footed_). The barnacles (_Lepas_) and the acorn-shells (_Balanus_) are familiar examples.
CIRRO-CUMULUS. This, the _sonder-cloud_, or system of small roundish clouds in the upper regions of the atmosphere, commonly moves in a different current of air from that which is blowing at the earth's surface. It forms the mackerel sky alluded to in the following distich:--
"A mack'rel sky and mares'-tails Make lofty ships carry low sails."
CIRRO-STRATUS. Is the stratus of the upper regions of the atmosphere, heavier looking than the cirrus, but not so heavy as the stratus.
CIRRUS. The elegant modification of elevated clouds, usually termed mares'-tails (see the distich given at CIRRO-CUMULUS); otherwise the curl-cloud.
CISCO. A fish of the herring kind, of which thousands of barrels are annually taken and salted in Lake Ontario.