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. CISTERN. A reservoir for water placed in different parts of a ship, where a constant supply may be required. Also furnished with a leaden pipe, which goes through the ship's side, whereby it is occasionally filled with sea-water, and which is thence pumped up to wash the decks, &c. CITADEL. A fortified work of superior strength, and dominating everything else, generally separated therefrom by an open space of glacis or esplanade; often useful against domestic as well as foreign enemies. CIVIL BRANCH. That department executed by civilians, as contradistinguished from the army or navy branch. CIVILIANS. The surgeon, chaplain, purser or paymaster, assistant surgeons, secretary, and ship clerks, on board men-of-war. CIVIL LORD. The lay or junior member of the admiralty board. CIVIL WAR. That between subjects of the same realm, or between factions of the same state. CLAIMANTS. Persons appealing to the jurisdiction of the admiralty court. They are denominated colourable, or fair, according to the informality, or justice, of their claims.