AQU 



APPU'LSE {appello, to drive to). The 

 near approach of two celestial bodies to 

 each other in angular distance, so as to 

 be seen, for instance, within the field of 

 a telescope. 



APRIO'RI. A POSTERIO'RI. Terms 

 expressive of two different modes of rea- 

 soning. By the argument a priori^ a 

 conclusion is drawn from an antecedent 

 fact, whether the consequence be in the 

 order of time, or in the necessary rela- 

 tion of cause and effect. By the argu- 

 ment a posteriori, we reason from what 

 is consequent in the order of time to 

 what is antecedent, or from effect to 

 cause. An individual may fall under 

 suspicion of murder for two reasons : he 

 may have coveted the deceased's pro- 

 perty, or he may be found with it in his 

 possession ; the former is an a priori, the 

 latter an a posteriori argument against 

 him. 



A'PSIDES {aVi^, a curved link of a 

 chain). Apses. Those points in a planet's 

 orbit, in which it is at its greatest or least 

 distance from the sun or earth. The 

 line joining them, and passing through 

 the sun's or the earth's centre, is called 

 the line of the apsides. This term occa- 

 sionally coincides with other terms. 

 Tims, in the orbit of the earth, or of any 

 primary planet, its higher apsis is also its 

 aphelion, its lower apsis its perihelion ; in 

 the moon's orbit, the higher apsis is equi- 

 valent to the apogee, the lower apsis to 

 the perigee. 



A'PTERA (a, priv., nrepov, a Aving). 

 A series of insects characterized by the 

 absence of wings. Some of these do not 

 undergo metamorphosis ; these compose 

 the orders thysanoura and parasita, while 

 those which undergo this change, form 

 the order syphonaptera. 



A'PUS (aTTour, without feet). Avis In- 

 dica. Bird of Paradise; a constell.ition 

 in the southern hemisphere, consisting 

 of eleven stars. The bird of Paradise 

 was formerly supposed to have no feet. 



ATYROUS (a, priv., ttvp, fire). A 

 term applied to bodies which sustain the 

 action of a strong heat for a long time 

 w^ithout change of figure or other proper- 

 ties. It is synonymous with refractory. 



AQUA FORTIS. An impure nitric 

 acid, distinguished by the terms double 

 and single, the latter having only half 

 t)ie strength of the former. The more 

 concentrated acid, which is much stronger 

 than the double aqua fortis, is called by 

 artists spirit of nitre. 



AQUA MARINE. A designation of 

 35 



A R A 



beryl, a mineral of a green colour of 

 various shades, also called greenish- 

 yellow emerald. 



AQUA REG! A.. Royal water ; an al- 

 chemical designation of nitro-muriatic 

 acid, from its property of dissolving gold, 

 the king of metals. 



AQUA'RIUS. The eleventh of the 

 zodiacal constellations, consisting of 108 

 stars, the principal of which is Scheat. 

 It presided over the second month of 

 summer, and extended from the 2()th of 

 July to the 20th of August. The inun- 

 dation of the Nile increases during this 

 month. 



A'QUEOUS {aqua, water). A terra 

 synonymous with hydrate, and employed 

 for expressing definite combinations with 

 water. It admits of prefixes, as bin- 

 aqueous, when two atoms of water enter 

 into a compound. 



A'QUEOUS ROCKS. A term applied 

 in geology to rocks of the second and 

 third classes, as composed of matter de- 

 posited by water. Those of the second 

 class are more especially named meta- 

 morphic, from the supposition of their 

 having undergone a remarkable change 

 in the course of their formation. Aque- 

 ous rocks are likewise called stratified, as 

 being invariably found in strata or layers. 



AQUIFOLIA'CE^. The Holly tribe 

 of Dicotyledonous plants, named from 

 the typical genus aquifolium. Trees or 

 shrubs, with leaves alternate or opposite, 

 coriaceous ; corolla 4 or 5-parted, hypo- 

 gynous; ovary fleshy, superior, 2-4-celled ; 

 fruit fleshy, indehiscent, with 2 to 6 stones. 



A'QUILA. The Eagle; a northern 

 constellation, containing (with Antinous) 

 seventy-one stars, the principal of which 

 is Altan. 



AQUILARIA'CE^. The Agallochum 

 tribe of Dicotyledonous plants, named 

 from the typical genus aquilaria. Trees 

 with leaves alternate ; calyx turbinate or 

 tubular; stamens 10 or 5; ovary supe- 

 rior; capsule pear-shaped, 1-celled, 2- 

 valved. 



AQUITE'L./E {aqua, water, tela, a 

 web). A family of spiders, which spread 

 their silken filaments under water, to en- 

 trap aquatic insects. 



A'RA. The Altar ; a southern con- 

 stellation, containing nine stars. 



ARA'CEiE. Aroidecs. The Arum tribe 

 of Monocotyledonous plants. Herbace- 

 ous plants with leaves sheathing at the 

 \ia.'&Q; flowers unisexual, arranged upon 

 a spadix, within a spathe ; stamens hypo- 

 gynous; ovory superior ; fruit succulent. 

 ' C6 ^ 



