A C C 



ACE 



meridian to-morrow three minutes and 

 fifty-six seconds before twelve o'clock. 



2. Acceleration of the planets. The 

 motion of the planets varies in different 

 parts of their orbits, according as they 

 are at a greater or less distance from the 

 sun. From their aphelion to their peri- 

 helion their motion is accelerate, i ; from 

 their perihelion to their aphelion it is 

 retarded. The average of these motions 

 through the whole orbit (the space di- 

 vided by the time) is called the mean 

 motion. Hence, the acceleration of a 

 planet is the excess of its real diur- 

 nal motion over its mean diurnal mo- 

 tion. 



3. Secular acceleration of the moon's 

 mean motion. An increase in the velo- 

 city of the moon's mean motion around 

 the earth. It amounts to about 11 se- 

 conds per century — a quantity small in 

 itself, but becoming considerable by its 

 accumulation during a succession of 

 ages. 



A'CCENT {accentus, from accino, to 

 sing in concert). A peculiar stress or 

 elevation of the voice, which distin- 

 guishes one syllable in every word which 

 consists of more than one syllable. The 

 syllable so distinguished is said to have 

 the acute accent, which is marked thus 

 (') ; ihs grave ( ), which is seldom marked, 

 is supposed to be placed over those syl- 

 lables which are pronounced without the 

 elevation of the voice ; the circumflex 

 C or ") is supposed to be formed by a 

 combination of the acute and the grave, 

 and hence is usually placed over con- 

 tracted syllables. In modern languages 

 the accent, when it falls upon a short syl- 

 lable, has, in most cases, the same effect 

 as if it were long ; but in the ancient 

 languages, accent and quantity were dis- 

 tinguished from each other. 



ACCENTS, MATHEMATICAL. Dif- 

 ferent magnitudes of the same kind, or 

 magnitudes placed in similar positions, 

 are denoted, in algebraical calculations, 

 by the use of the same letter distin- 

 guished by accents. The accented letter 

 a' is read a accented or a dashed; a" is 

 read a twice accented, or a twice dashed, 

 or, more commonly, a two dash. When 

 accents are inconveniently numerous, 

 Roman figures are employed : thus a'^ is 

 used instead of a"". The accented letter 

 is the metaphor of algebra. 



A'CCESSORY VALVES {accedo, to be 

 added). Small additional valves placed 

 near the umbones or bosses of the genus 

 pholas among shells, and on the edges of 



the pedunculated barnacles, among an- 

 nulose animals. 



A'CCIDENT [accido, to happen to). 

 This term, in its widest technical sense, 

 denotes any thing which can be attri- 

 buted to an object, and can only be con- 

 ceived as belonging to some substance, 

 in which sense it is opposed to " sub- 

 stance." In its more restricted and logi- 

 cal sense, it is a predicable, which may be 

 absent or present, the essence of the 

 species remaining the same. An acci- 

 dent is called separable, when it may be 

 separated from the individual ; insepa- 

 rable, when it cannot be separated from 

 the individual : the word '• individual " 

 is here emphatic, because every accident 

 must be separable from the species, else 

 it would be a property. 



ACCI'PITRES {accipiter, a hawk). 

 Raptores. Rapacious birds; birds of 

 prey ; known by their hooked beak and 

 talons. They are distinguished into the 

 diurnal and the nocturnal ; the former 

 comprising the falcons, eagles, vultures, 

 &c. ; the latter the owls. 



A'CCLIMA'TION. Naturalization to 

 a foreign or unusual climate ; a term ap- 

 plied to plants and animals. 



ACCRETION {accresco, to grow to). 

 The addition of new parts, as in the 

 formation of a crystal by the position of 

 new parts around a central nucleus. The 

 organic and inorganic kingdoms are dis- 

 tinguished by their mode of increase; 

 the former increasing by intussusception 

 and alimentation, the latter by accretion 

 without alimentation. 



ACCU'MBENT {accumho, to lie down). 

 Lying against any thing, as the edges of 

 tlie cotyledons against the radicle in some 

 cruciferous plants. See Incumbent. 



ACCU'SATIVE CASE {accuso, to ac- 

 cuse). Literally, the aiming at case ; a 

 case belonging to the Latin language, and 

 denoting, originally, the object to which 

 any motion or action is directed ; it was, 

 afterwards, employed to distinguish the 

 object of any action or feeling. It cor- 

 responds with the ohjective case, or the 

 objecty of the English Grammar. See 

 Case. 



-ACEOUS. Terminations in -aceous 

 denote a resemblance to a substance, as 

 membranaceous, resembling membrane; 

 whereas terminations in -ous denote the 

 substance itself, as membranous, belong- 

 ing to membrane. 



ACE'PHALA (a, priv., Ke0aX»/, the 

 head). Headless animals ; a class of the 

 Mollusca, which have no head, but simply 



