ALTERNATING WINDS. Peculiar winds blowing at stated times one way, and then, from a sudden alteration in the temperature of the elements, setting in the contrary direction. A remarkable instance is that of the Gulf of Arta in the Ionian Sea, where the effect is promoted by local causes. All land and sea breezes are strictly alternating winds. These however are mostly intertropical; the solar heat causing the sea-breeze to blow on the land by day, and condensation and greater heat of the sea causing a reaction when the land has cooled to a lower temperature.
ALTERNATION or Permutation of Quantities, is the varying or changing their order, and is easily found by a continual multiplication of all numbers.
ALTIMETRY. Trigonometry; the art of measuring heights or depressions of land, whether accessible or not.
ALTITUDE. The elevation of any of the heavenly bodies above the plane of the horizon, or its angular distance from the horizon, measured in the direction of a great circle passing through the zenith. Also the third dimension of a body, considered with regard to its elevation above the ground.—Apparent altitude is that which appears by sensible observations made on the surface of the globe.—Altitude of the pole. The arc of the meridian between the pole of the heavens and the horizon of any place, and therefore equal to its geographical latitude.—Altitude of the cone of the earth's and moon's shadow, is the height of the one or the other during an eclipse, and is measured from the centre of the body.—Altitude of a shot or shell. The perpendicular height of the vertex of the curve in which it moves above the horizon.—Meridian altitude. The arc of the meridian,—or greater or less altitude, measured from the horizon, of a celestial object in its passage over the meridian, above or below the pole, of the place of the observer. In Polar regions two such transits of the sun, and in England similarly, circumpolar stars afford double observations for the determination of time or latitude. The general term is understood by seamen to denote mid-day, when the passage and meridian altitude of the sun affords the latitude.—True altitude is that produced by correcting the apparent one for parallax and refraction.
ALTMIKLEC. A silver Turkish coin of 60 paras, or 2s. 91⁄2d. sterling.
ALUFFE, or Aloof. Nearer to the wind. This is a very old form of luff; being noticed by Matthew Paris, and other writers, as a sea-term. (See [Luff].)
ALURE. An old term for the gutter or drain along a battlement or parapet wall.
ALVEUS. A very small ancient boat, made from the single trunk of a tree. A monoxylon, or canoe.
A.M. The uncials for ante-meridian, or in the forenoon. (See [Meridian].)
AMAIN [Saxon a, and mægn, force, strength]. This was the old word to an enemy for "yield," and was written amayne and almayne. Its literal signification is, with force or vigour, all at once, suddenly; and it is generally used to anything which is moved by a tackle-fall, as "lower amain!" let run at once. When we used to demand the salute in the narrow seas, the lowering of the top-sail was called striking amain (see [Strike]), and it was demanded by the wave amain (see [Waving]), or brandishing a bright sword to and fro.