APPROXIMATION. A continual approach to a quantity sought, where there is no possibility of arriving at it exactly.
APPULSE. A near approach of one heavenly body to another, so as to form an apparent contact: the term is principally used with reference to stars or planets when the moon passes close to them without causing occultation.
APRON, OR STOMACH-PIECE. A strengthening compass timber fayed abaft the lower part of the stern, and above the foremost end of the keel; that is, from the head down to the fore dead-wood knee, to which it is scarfed. It is sided to receive the fastenings of the fore-hoods or planking of the bow.--_Apron of a gun_, a square piece of sheet-lead laid over the touch-hole for protecting the vent from damp; also over the gun-lock.--_Apron of a dock_, the platform rising where the gates are closed, and on which the sill is fastened down.
APSIDES, LINE OF. The imaginary line joining the aphelion and perihelion points in the orbit of a planet.
APSIS. Either of the two points in planetary orbits where they are at the greatest and the least distance from the sun, and are termed _higher_ or _lower_ accordingly. The two are joined by a diameter called the _line of the apsides_.
AQUAGE. The old law-term denoting the toll paid for water-carriage.
AQUARIUS. The eleventh sign in the zodiac (α Aquarius Sadalmelik).
AQUATIC. Inhabiting or relating to the water.
AQUATILE. An archaism for _aquatic_; thus Howell's lexicon describes the crocodile as "partly aquatil, partly terrestrial."
AQUATITES. The law-term for everything living in the water.
AQUE. Wall-sided flat-floored boats, which navigate the Rhine.
AQUEDUCT. Conduits or canals built for the conveyance of water.
AQUILA. The constellation Aquila, in which α Aquilæ is an important star of the first magnitude: used by seamen in determining the latitude and longitude; also in lunar distances. (_See_ ALTAIR.)
AQUILON. The north-east wind, formerly much dreaded by mariners.
ARAMECH. The Arabic name for the star Arcturus.
ARBALIST [from _arcus_ and _balista_]. An engine to throw stones, or the cross-bow used for bullets, darts, arrows, &c.; formerly arbalisters formed part of a naval force.
ARBITER. The judge to whom two persons refer their differences; not always judicial, but the arbiter, in his own person, of the fate of empires and peoples.