OBL 



OB L 



the value which it has when it stands 

 alone; that the second on the right hand 

 shall mean ten times as many as it does 

 when it stands alone; that the third 

 shall mean one hundred times as many 

 as when it stands alone ; the fourth, one 

 thousand times ; and so on. 



NUMERATOR. In arithmetic, that 

 part of a fraction which denotes how 

 many of the aliquot parts of an integer 

 or unit are taken, the nature of these 

 parts being expressed by the denomi- 

 nator. Thus I denotes five, not of units, 

 but of sixths of a unit; six is the deno- 

 minator, 5 the numerator or numberer 

 of the parts taken. 



NUMERICAL. In Algebra, this term 

 is applied to co-efBcients which consist of 

 numbers, as distinguished from literal 

 co-efficients, which consist of letters. As 

 opposed to algebraical, it is applied to the 

 magnitude of a quantity, considered irre- 

 spectively of its symbol; thus — 20 is 

 numerically greater than — 10, though 

 algebraically less. 



NU'MMULITES {nummus, money, Xi- 

 Sov, a stone). An extinct genus of the 

 order of molluscous animals, called Ce- 

 phalopods, of a thin lenticular shape, 

 resembling a coin, internally divided into 

 small chambers. 



NUT. A dry, bony, indehiscent, one- 

 celled fruit, proceeding from a pistil of 

 three cells, and enclosed in a cupule, as 



in the hazel, the acorn, &c. The term 

 is sometimes applied to the fruit of 

 borago, lithospermum, &c., but these 

 fruits are more properly called akenia. 

 The term mix baccata is sometimes ap- 

 plied to the fruit of taxus, &c. 



NUTA'TION {ntito, to nod). The 

 term applied to a small and slow gyratory 

 movement of the earth's axis, by which, 

 if subsisting alone, the pole would de- 

 scribe among the stars, in a period of 

 nineteen years, a minute ellipse, having 

 its longer axis equal to 18" 5, and its 

 shorter to 13"-74; the longer being di- 

 rected towards the pole of the ecliptic, 

 the shorter at right angles to it. 



NU'TTALITE. A mineral associated 

 with calc-spar, from Bolton in Massa- 

 chusetts. It appears to be an alumino- 

 silicate of lime, potash, and iron. 



NYCTERIBFIDiE. The Bat-lice; a 

 family of dipterous pupiparous insects, 

 parasitic on bats, and approaching to 

 the spiders in form. 



NYMPH. A fanciful term for the 

 chrysalis or pupa state of insect life, ap- 

 plied to the active pupae of orthopterous 

 and hemipterous insects. 



NYSSO'NIDiE. A family of hymeno- 

 pterous insects belonging to the section 

 Fossores, named from the genus Nysson, 

 and characterized principally by the 

 absence of a notch on the inner side of 

 the mandibles. 



O 



0B-. A Latin preposition, in compo- 

 sition signifying inversion : thus o6-ovate 

 means inversely ovate ; o6-conical, in- 

 versely conical. It is obvious that this 

 term can only be employed in words 

 which denote that one end of a body is 

 wider than the other. Hence, it is super- 

 fluous in such a word as o6-lanceolate. 



OBJECTIONS, FALLACY OF. A 

 fallacious mode of argument, by which 

 it is shown that there are objections 

 against some plan, theory, or system, 

 and thence it is inferred that it should 

 be rejected ; whereas that which ought 

 to have been proved is, that there are 

 more or stronger objections against the 

 receiving than the rejecting of it. 



OBLATE. A term signifying the re- 

 verse of oblong, or shorter in one direc- 

 tion than in another, and applied to a 

 238 



spheroid which is made by the revolution 

 of an ellipse about the smaller of the 

 two axes. Thus the earth is an oblate 

 spheroid, the actual difference between 

 the polar and the equatorial diameters 

 being in the proportion of 300 to 301. 



OBLIQUE. A term generally em- 

 ployed in opposition to direct or right. 

 In astronomical language, the term ob- 

 liquity denotes the angle made by the 

 ecliptic with the equator. The greatest 

 latitude at which the sun ever appears 

 vertical is the obliquity of the ecliptic 

 (See Ascension). In stereographic pro- 

 jection, an oblique circle is any circle 

 oblique to the line of projection. Oblique 

 planes, in dialling, are planes which re- 

 cline from the zenith. Oblique projection, 

 in mechanics, is the projection of a body 

 at an oblique angle with the horizontal 



