NEM 



NEU 



the third ; there is a ' physical necessity ' 

 for the fall of a stone ; and a ' moral 

 necessity ' that beings of a certain cha- 

 racter should act, when left perfectly 

 free, conformably to that character ; i. e. 

 we are sure they will act so ; though, of 

 course, if, is in their power to act other- 

 wise." The ambiguity consists in con- 

 founding the second and the third kinds 

 of necessity, and thus finding an excuse 

 for immoral conduct. — Whately. 



NECESSARY MATTER. In Logic, 

 the necessary matter of a proposition 

 denotes the essential or invariable agree- 

 ment of its terms. In necessary matter, 

 all affirmatives are true, and negatives 

 false; in impossible matter, vice versd; 

 in contingent matter, all universals are 

 false, and particulars true. 



NE'CROMITE. A white mineral 

 found near Baltimore, in small masses, 

 in limestone. 



NE'CTARY. That part of a flower 

 which secretes nectar or honey. The 

 term has been vaguely applied to several 

 parts which have no such function. 



NEEDLE-ORE. A triple sulphuret 

 of bismuth, lead, and copper, also called 

 acicular bismuth glance. 



NEEDLE-STONE. A zeolitic sub- 

 stance of a grej ish-white colour, found in 

 secondary trap rocks near Old Kilpatrick 

 in Scotland. 



NEGATION, CONVERSION BY. In 

 logic, a mode of illative conversion, com- 

 monly called by contra-posilion. Thus it 

 may be said—" Every poet is a man of 

 genius ; therefore, he who is not a man 

 of genius is not a poet;" for it is the 

 same thing to affirm some attribute of 

 the subject, or to deny the absence of that 

 attribute. 



NEGATIVE QUANTITY. In alge- 

 bra, any quantity to which the sign — is 

 prefixed, is called a negative quantity. 

 The explanation of such a quantity is a 

 difficult matter. It is, however, usually 

 defined, either as a quantity less than 

 nothing, or as a quantity of the same 

 nature as a positive quantity, but ^ taken 

 in a contrary sense or in an opposite 

 direction. See Quantity. 



NEGATIVE TERM. In logic, a ne- 

 gative term denotes that a certain view 

 is not and could not be formed of a par- 

 ticular object, as a "dumb statue," a 

 "lifeless carcass." Compare Privative. 



NEMATOI'DEA {vnixa, vtjfxarof, a 



thread, etao?, likeness). Round worms ; 



an order of the Entozoa, which have a 



long, cylindrical, and often filiform, 



232 



naked, iiiarticulated body, traversed by 

 a straight alimentary canal open at both 

 ends. These are the cavitary intestinal 

 worms of Cuvier, the stcrelmintha of 

 Owen. 



NE'MATONEU'RA {v7)iJLa, v^naro^, 

 a thread, vevpov, a nerve). A term ap- 

 plied by Owen to a division of the 

 Radiata of Cuvier, in which the nervous 

 matter is distinctly aggregated into fila- 

 ments, and in some cases nuclei of rudi- 

 mentary nervous centres have been 

 noticed. 



NEMO'CERA {vn/jia, a thread, Kepat, 

 a horn). A section of Dipterous insects, 

 characterized by their long filiform an- 

 tennae, composed of more than six joints. 



NE'PHELINE (vetpeXri, a cloud). 

 Sommite. Rhomboidal feldspar, occurring 

 at Monte Somma, near Naples, in granu- 

 lar limestone, and in the lava of Capo di 

 Bove, near Rome. In nitric acid its 

 transparent fragments become cloudy. 



NEPHRITE (i/e0p6f, a kidney). Jade. 

 A mineral occurring in gneiss and gra- 

 nite. It comprises the common variety 

 and axestone. The South America va- 

 riety is called Amazonian stone, from 

 its locality. It was formerly used, as an 

 amulet, in nephritic complaints. 



NE'PIDiE. A family of the Hydro- 

 corisa, or Water Bugs, resembling the 

 Notonectidae, or boat-flies, in structure 

 and in habits, but endowed with slower 

 powers of motion. 



NEPTU'NIAN THEORY. A geolo- 

 gical theory of Werner, which refers the 

 formation of rocks and strata to an aque- 

 ous origin. 



NEREIDtE. a common name for a 

 highly organized order of Annellida,t3Lken 

 from the Linnsean generic name Nereis, 

 which is almost equivalent to the ordinal 

 designation Errantes of Milne Edwards. 

 These are the dorsibranchiata of Cuvier, 

 the sea-centipedes and sea-mice of popu- 

 lar language. 



NERI'TINiE. A sub-family of the 

 Naticidce, or Nerits, named from the 

 genus neritina ; in these shells the spire 

 is often nearly or quite obsolete. 



NE'RVURES {nervus, a sinew). The 

 delicate frame-work of the membranous 

 wings of insects. 



NEURO'PTERA {vevpov, a nerve, 

 TTTepov, a wing). An order of insects 

 furnished with four membranous wings, 

 which are naked and reticulated with 

 ramified tracheae. It includes the dra- 

 gon-flies, may-flies, ant-lions, white 

 ants, &c. 



