av<^" 



AC A 



ACC 



reference, merely to indicate a certain 

 number of units of the same kind, as 

 when we simply say 3, 4, 5, they are 

 called abstract numbers. The multipli- 

 cation table is a series of abstract num- 

 bers. See Abstraction. 



ABSTRA'CTION {abstraho, to draw 

 off). The operation of the mind by 

 which we draw off, and contemplate sepa- 

 rately, some portion or property of an 

 object, as the scent of a rose, disregard- 

 ing all else that belongs to it. The ope- 

 ration, therefore, strictly speaking, may 

 be limited to the contemplation of a single 

 object. But the term is usually employed 

 in a wider sense: in contemplating several 

 objects which agree in certain points, we 

 abstract the circumstances of agreement, 

 disregarding the differences, and give to 

 all and each of these circumstances a 

 common name, expressive of this agree- 

 ment ; we are then, properly, said to 

 generalize. Abstraction, therefore, does 

 not necessarily imply generalization, 

 though generalization implies abstrac- 

 tion. 



ABSU'RDUM, REDUCTIO AD. A 

 form of argument, frequently employed 

 in geometrical reasoning, by which, in- 

 stead of proving the thing asserted, the 

 absurdity is shown of every thing which 

 contradicts that assertion. For it follows 

 that, if every thing which contradicts a 

 proposition be false, the proposition itself 

 must be true. 



ABU'NDANT NUMBER. Any num- 

 ber which is less than the sum of its di- 

 visors, as 12, which is less than the sum 

 of / 2, 3, 4, and 6, all of which are its 

 divisors, and their sum is 16. A deficient 

 number is that which is greater than the 

 sum of its divisors ; a perfect number, 

 that which is^equal to the sum of its di- 

 visors^'^^ 



ACALE'PHiE [lxKa\i](t>r\, a nettle). Sea- 

 nettles ; a class of gelatinous zoophytes, 

 found in the water of the ocean, and so 

 named from the stinging sensation which 

 many of them produce when touched. 

 To this class belong the sea-jelly, sea- 

 nettle, Portuguese man-of-war, &c. By 

 the old naturalists they were known by the 

 title of urtlcee marines. See Malactinia. 

 ACA'NTH A {uKavOa, a thorn). A spine, 

 or prickle ot a plant. A prickly fin of a 

 fish. A spinous process of a vertebra. 



ACANTHA'CE^. The Justicia tribe 

 of Dicotyledonous plants, named from 

 the genus Acanthus. Herbaceous plants 

 or shrubs, with leaves opposite ; corolla 

 gamopetalous ; stamens mostly 2 ; capsule 

 3 



2-cened, bursting elastically with 2 valves; 

 seeds usually hooked, exalbuminous. 



ACANTHA'LES. An alliance of Dico- 

 tyledonous plants. Flowers unsymme- 

 trical, usually didynamous. Seeds ad- 

 hering to hard hook like processes of the 

 placenta. Albumen 0. Calyx 4-5-leaved, 

 remarkably imbricated, as if in more 

 whorls than one ; often enveloped in 

 large bracts. 



ACA'NTHOCE'PHALA {'dKavOa, a 

 spine, Ke0aX>;, the head). Hooked 

 worms; an order of the Entozoa, which 

 have an elongated cylindrical body, with 

 the anterior part closely covered with 

 small sharp spines, and the oral aper- 

 ture leading to a ramified alimentary 

 canal. 



ACA'NTHOPTERY'GII (aKav6>a, a 

 thorn, irrepvfiov, a. fin). Spinous-finned 

 fishes, or fishes whose dorsal fins are bony 

 and prickly ; one of the three primary 

 grand divisions, or natural orders of 

 fishes, established by Cuvier. The order 

 comprises fifteen families. 



ACA'NTICONE. A sub-species of 

 prismatoidal augite, occurring in primi- 

 tive beds and veins, in Norway and other 

 parts. It is of a pistachio-green colour, 

 and is known by the names pistacite and 

 epidote. 



A'CARIDiE. A family of the Arach- 

 nida, belonging to the order Tracheata, 

 and named from the typical genus acarus, 

 to which the mite, the tick, the water- 

 mite, and the flesh- worm belong. The 

 last of these is distinguished from the 

 rest by the presence of only six feet. 



ACAULE'SCENT (a, priv., KauXor, a 

 stalk). Stemless ; a term applied to a 

 plant in which the stem is apparently 

 absent, and the leaves seem to rise from 

 the root, as in Cnicus acaulis. As, how- 

 ever, according to the theory of vegetable 

 development, a stem is assumed to exist, 

 the term subcaulescent would be prefer- 

 able. 



ACCELERATION {accelero, to has- 

 ten). The increase of the motion of 

 moving bodies. Thus, a stone, falling to 

 the earth, moves faster and faster as it 

 descends ; its motion is therefore said 

 to be continually accelerated ; in other 

 words, its velocity continually increases. 

 1. Acceleration of the fixed stars. The 

 time by which the stars, in their diurnal 

 revolution, anticipate the mean diurnal 

 revolution of the sun ; which is three 

 minutes and fifty-six seconds. Thus, a 

 star, which to-day passes the meridian at 

 twelve o'clock, mean time, will pass the 

 B2 



