AST 



AST 



nets ire celestial bodies, of a considerable 

 size and small eccentricity of orbit, mov- 

 ing in planes that do not deviate many de- 

 grees from that of the earth, in a direct 

 course, and in orbits at considerable dis- 

 tances from each other, with atmospheres 

 of considerable extent; but bearing 1 hard- 

 ly any sensible proportion to their diame- 

 ters, and having satellites or rings : and 

 comets are very small celestial bodies, 

 moving in directions wholly undetermin- 

 ed, and in very eccentric or apparently 

 parabolic orbits, situated in every variety 

 of position, and having very extensive at- 

 mospheres. Dr. Herschell, having com- 

 pared the newly discovered stars by the 

 criteria introduced in the above defini- 

 tions, maintains, that they differ in so ma- 

 ny respects from both planets and comets, 

 as to warrant his not referring them to 

 either of these two classes. 



ASTHMA, in medicine, a painful, diffi- 

 cult, and laborious respiration. See ME- 

 BICIXE. 



ASTRjE A, in astronomy, the same with 

 Virgo. See VTRGO. 



ASTRAGAL, in architecture, the neck 

 moulding of a column, composed of a 

 beed and fillet. 



ASTRAGAL, in gunnery, a round mould- 

 ing encompassing a cannon, about half a 

 foot from its mouth. 



ASTRAGALUS, milk-vetch, in botany, 

 a genus of the Diadelphia Decandria class 

 of plants, with a papilionaceous flower, 

 and bilocular-podded fruit, containing 

 kidney-like seeds. There are upwards of 

 60 species ; all of which may be raised 

 from seeds. They are in general hardy, 

 and require no other care but to draw 

 the plants out when they come up too 

 thick, leaving them at least eighteen 

 inches asunder. The American species 

 are 5 in number. 



ASTRAGALUS, in anatomy, called also the 

 talus, is the superior and first bone of the 

 foot, according to its natural situation and 

 connection with the leg, being articulat- 

 ed with the tibia and fibula, and with the 

 ealcaneum ; having its head formed for 

 the articulation with the os naviculare. 



ASTRAL, something belonging to or 

 connected with the stars : thus, astral year 

 is the same with sideral year. 



ASTRANTIA, black master-wort, in bo- 

 tany, a genus of umbelliferous plants, be- 

 longing to the Penlandria Digynia class 

 of Linnaeus, the flower of which is rosace- 

 ous, and collected into a sort of head ; and 

 its fruit is oval, obtuse, coronated, and 

 striated 



ASTROLABE, an instrument for taking 

 the altitude of the sun or stars at sea, be- 



ing a large brass ring, the limb of which, 

 or a convenient part thereof, is divided 

 into degrees and minutes, with a move- 

 able index, which turns upon the centre, 

 and turns two sights : at the zenith is a 

 ring to hang it by in time of observation, 

 when you need only turn the index to the 

 sun, that the rays may passfreely through 

 both sights, and the edge of the index 

 cuts the altitude upon the divided limb. 

 This instrument, though not much in use 

 now, if well made, and of great weight, 

 that it may hang the steadier, is as good 

 as most instruments that are used at sea 

 for taking altitudes, especially between 

 the tropics, when the sun comes near the 

 zenith, and in calm weather. 



ASTROLOGY, a conjectural and truly 

 absurd science, which teaches to judge 

 of the effects and influences of the stars, 

 and to fortel future events by the situa- 

 tion and different aspects of the heavenly 

 bodies. It may be divided into two 

 branches, natural and judiciary ; the for- 

 mer being the prediction of naturaleffects, 

 as the changes of weather, winds, storms, 

 hurricanes, thunder, floods, earthquakes, 

 &c. and the latter, that which pretends to 

 foretel moral events, or such as have a 

 dependence on the freedom of the will. 



ASTRONIUM, in botany, a genus of 

 the Dioecia Pentandria class and order of 

 plants. The essential character is, male, 

 calyx five-leaved; corol five petalled. 

 Female, calyx five-leaved; corol five- 

 petalled ; styles three, and one seed. 

 There is but one species, the A. graveo- 

 lens, an upright tree, from 12 to 30 feet 

 in height, abounding every where in a 

 slightly glutinous terebinthine juice. Af- 

 ter the fruits in the female, and the flow- 

 ers in the male plant have fallen off, new 

 branches are put forth. The flowers are 

 small and red, the calyxes are expanded 

 into stars, nearly an inch in diameter. It 

 is native in the woods about Carthagena 

 in New Spain. 



ASTRONOMY, is the science which 

 treats of the motions, periods, eclipses, 

 magnitudes, &c. of the heavenly bodies, 

 of the laws by which these are regulated, 

 and of the causes on which they depend. 

 It is unquestionably the most sublime of 

 all the sciences. No subject has been 

 longer or more successfully studied. Al- 

 though it may be interesting to take a 

 brief sketch of the history of this science, 

 yet there can be no comparison drawn be- 

 tween the wide observations of the earlier 

 observers, and the precision and general 

 views of modern astronomers. To ascer- 

 jtain the real motions of the heavenly bo- 



