AXIS. The imaginary line upon which a planet revolves, the extremities of which are termed the poles,--therefore a line joining the north and south poles. The real or imaginary line that passes through the centre of any cylindrical or spherical body on which it may revolve. Also a right line proceeding from the vertex of a cone to the middle of its base. Also, an imaginary right line passing through the middle of a ship perpendicularly to its base, and equally distant from its sides;--an imaginary line passing through the centre of a gun's bore, parallel with its position.--_Axis of a telescope._ (_See_ COLLIMATION, LINE OF.) AXLE-TREES. The two cross-pieces of a gun-carriage, fixed across and under the fore and hinder parts of the cheeks. The cylindrical iron which goes through the wheel of the chain-pump, and bears the weight of it. AYE, AYE, SIR. A prompt reply on receiving an order. Also the answer on comprehending an order. _Aye-aye_, the answer to a sentinel's hail, from a boat which has a commissioned officer on board below the rank of captain. The name of the ship in reply from the boat indicates the presence of a captain. The word "flag," indicates the presence of an admiral. AYLET. The sea-swallow. AYONT. Beyond. AYR. An open sea-beach, and also a bank of sand. (_See_ AIRE.) The mediæval term for _oar_. AYT. _See_ EYGHT. AZIMUTH. A word borrowed from the Arabic. The complement of the amplitude, or an arc between the meridian of a place and any given vertical line. AZIMUTHAL ERROR. _See_ MERIDIAN ERROR. AZIMUTH CIRCLES. _See_ VERTICAL CIRCLES. AZIMUTH COMPASS. A superior graduated compass for ascertaining the amount of magnetic variation, by amplitude or azimuth, when the sun is from 8° to 15° high, either after its rising or before its setting. (_See_ MAGNETIC AZIMUTH.) It is fitted with vertical sight vanes for the purpose of observing objects elevated above the horizon. AZOGUE. [Sp.] Quicksilver. AZOGUES. Spanish ships fitted expressly for carrying quicksilver. AZUMBRE. A Spanish wine-measure, eight of which make an arroba. AZURE. The deep blue colour of the sky, when perfectly cloudless. B. BAARD. A mediæval transport. BAARE-Y-LANE. The Manx or Gaelic term for high-water. BAAS. An old term for the skipper of a Dutch trader. BAB. The Arabic for _mouth_ or _gate_; especially used by seamen for the entrance of the Red Sea, _Bab-el-mandeb_. BABBING. An east-country method of catching crabs, by enticing them to the surface of the water with baited lines, and then taking them with a landing net. BABBLING. The sound made by shallow rivers flowing over stony beds. BAC. A large flat-bottomed French ferry-boat. In local names it denotes a ferry or place of boating. BACALLAO [Sp.] A name given to Newfoundland and its adjacent islands, whence the epithet is also applied to the cod-fish salted there. BACCHI. Two ancient warlike machines; the one resembled a battering-ram, the other cast out fire.