AST 



ATA 



stance, also called bitumen Judaicum, or 

 Jews' pitch, forming in lumps on the 

 surface of some waters, especially near 

 Babylon, and employed by the Egyptians 

 for embalming, under the name of mu- 

 mia mineralis. 



ASPHODE'LEiE. The Asphodel or 

 Lily tribe of Monocotyledonous plants. 

 Herbaceous plants, with bulbs, occa- 

 sionally arborescent, with leaves not arti- 

 culated with the stem, parallel-veined ; 

 flowers hexapetaloideous ; stamens hypo- 

 gynous ; ovary superior ; fruit succulent 

 or dry and capsular. 



ASSA'YING. The chemical operation 

 of ascertaining the quantity of any metal 

 in an ore or mixture. It differs from 

 Analysis only in degree, and is performed 

 in the dry way, as by heat ; in the moist 

 way, as by acids and other re-agents ; or 

 by both methods. See Cupellation. 



ASSIMILA'TION (assimilo, to liken 

 to). The function by which organized 

 bodies convert aliment into their own 

 proper substance. 



ASSOCIATE MOVEMENTS. Con^ 

 sensual Movements. Those 'movements 

 which, contrary to our will, accompany 

 other, voluntary, motions. Thus, the eye 

 cannot be moved inwards by the action of 

 the rectus internus, without contraction 

 of the iris being produced. 



ASTA'TIC (a, priv., ardo), to stand). 

 A term applied to a magnetic needle, 

 when its directive property is destroyed 

 by the proximity of another needle of 

 equal magnetic intensity, fixed parallel 

 to it, and in a reversed position, each 

 needle having its north pole adjacent to 

 the south pole of the other. In this state 

 the needles, neutralizing each other, are 

 unaffected by the magnetism of the earth, 

 while they are still subject to the influence 

 of galvanism. 



ASTE'RIA (uo-T^p, a star). A variety 

 of sapphire, showing a star-like opa- 

 lescence in the direction of the axis, 

 "When cut round. 



ASTE'RISM {ucr'rjp, a star). A small 

 cluster of stars, either distant from, or 

 forming a part of, a constellation. 



ASTEROPDA {aorijp, a star, e'i6os, 

 likeness). An order of the polypipherous 

 Radiata, named from the star-shaped 

 form presented by the ten taenia, when 

 expanded^ They may be also termed 

 Alcyonian polypiphera, from the name of 

 one of the principal groups. 



A'STEROIDS ((io-T^jp, a star, eJSoc, 

 likeness). A term applied by Herschel 

 to the recently discovered planets, Ceres, 

 41 



Juno, Pallas, and Vesta, and including 

 those celestial bodies which move in 

 orbits of any eccentricity round the sun, 

 whatever angle their orbits make with 

 the ecliptic, whether the motion of these 

 bodies be direct or retrograde, whether 

 they have or have not atmospheres, 



ASTRI'NGENT PRINCIPLE. A 

 principle existing in the gall-nut and 

 other substances, and characterized by 

 the property of contracting the muscular 

 fibre. From the use of this principle in 

 tanning skins, it has been called tannin. 



A'STROLABE {aarpov, a star, \a^x- 

 /3dv(i}, to take). Planisphere. A pro- 

 jection of the sphere upon the plane of 

 one of the great circles : it is furnished 

 with a graduated rim, to which sights are 

 added, for the purpose of taking altitudes. 



ASTRO'LOGY (ao-rpoi/, a star, \6yo^, 

 an account). A term strictly meaning 

 the science of the stars, but applied to 

 the pretended discovery of future events 

 by means of the position of the heavenly 

 bodies. 



ASTRO'NOMY {'darpuv, a star, v6/xof, 

 a law). The science which treats of the 

 motions, the distances, the size, the phy- 

 sical constitution, the eclipses, and all 

 other phenomena of the heavenly bodies. 

 By the term astra, the ancients under- 

 stood not only the stars, properly so 

 called, but also the sun, the moon, and 

 all the bodies which compose the visible 

 universe. 



1. Descriptive astronomy demonstrates 

 the magnitudes, distances, and densities 

 of the heavenly bodies, and explains 

 the phenomena dependent on their mo- 

 tions, as the change of seasons, and the 

 vicissitudes of day and night. 



2. Physical astronomy explains the 

 theory of planetary motion, and the laws 

 by which this motion is regulated and 

 sustained. 



3. Practical astronomy details the de- 

 scription and use of astronomical in- 

 struments, and develops the nature and 

 application of astronomical calculations. 



ASY'MPTOTES {uavfxnTcoTos, that 

 which does not fall with). A term ap- 

 plied to two lines (one of which, at least, 

 must be a curve), which, although con- 

 tinually approaching nearer and nearer, 

 and although indefinitely produced, never 

 meet each other. This properly occurs in 

 the hyperbola, and appears of a paradox- 

 ical character. 



ATA'CAMITE. A native muriate of 

 copper, found in the desert of Atacama, 

 between Chili and Peru. It occurs in a 



