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NA'CREOUS {nacre, pearl). A term 

 applied to a shell which has a pearly 

 lustre and reflects iridescent light. 



NACRITE. The name given by 

 Jameson to talcire, or the earthy talc of 

 Werner; a very rare mineral, occurring 

 in veins, with sparry ironstone and ga- 

 lena, in the mining district of Freyberg. 



NADIR. An Arabic term denoting 

 that point of the sphere of the heavens 

 which is diametrically opposite to the 

 zenith, and vertically beneath the feet of 

 a spectator. The term evidently cor- 

 responds with the German nieder (down). 

 The zenith and the nadir are the two 

 poles of the horizon. See Zenith. 



NADLESTEIN. Another name for 

 rutile, an ore of titanium. 



NAGYAG ORE. Foliated tellurium, 

 a mineral consisting of tellurium and 

 lead. 



NAFADES. A family of fresh-water 

 conchiferous mollusks, comprising the 

 genera unio, hyria, anodon, and iridina, 

 occurring abundantly in the North Ame- 

 rican rivers. 



NAKED SEEDS. An incorrect term, 

 applied by Linnaean botanists to the 

 small seed-like fruits of the Labiatae, 

 Boraginaceae, and other families of plants. 

 Seeds entirely destitute of a pericarp 

 occur only in Coniferae, Cycadaceae, and 

 Gnetaceae. 



NAKER FELDSPAR. A species of 

 feldspar, also called adularia, and found 

 principally on Mount St. Gothard, but 

 not in the valley of Adula, from which 

 the latter name is derived. The fine 

 variety from Ceylon, when cut en carbo- 

 chon, is called moonstone ; and a yellow 

 naker feldspar with reddish dots has ob- 

 tained the name of sunstone, which is 

 also sometimes given to the beautiful 

 avanturino variety of common feldspar. 



NANCE'IC ACID. An acid found in 

 many acescent vegetable substances, and 

 named by Braconnot from the town of 

 Nancy 



NAPHTHA. A highly inflammable, 

 thin, colourless oil, which issues from 

 the white, yellow, or black clays in Persia 

 and Media, and of which there are 

 springs in many countries, particularly 

 in volcanic districts. Black Naphtha is 

 230 



a common name for petroleum, or rock 

 oil. 



NAPHTHALINE. A greyish white 

 substance found during the rectification 

 of the petroleum of the coal gas works, 

 incrusting the pipes. Mineral or resin- 

 ous Caphthaline has been found native 

 in a layer of lignite, in the coal forma- 

 tion of Uznach. 



NAPIER'S RODS, or BONES. A 

 contrivance for facilitating the mecha- 

 nical performance of nmltiplication and 

 division. The invention has been super- 

 seded by the discovery of logarithms. 



NAPLES YELLOW. A pigment pre- 

 pared by calcining lead with antimony 

 and potash in a reverberatory furnace, 

 formerly made at Naples. 



NAPO'LEON. A name given to the 

 constellation Orion, 



NASCENT STATE {nascor, to be 

 born). A term applied to the state of 

 gases, at the moment of their generation, 

 before they have acquired the repulsive 

 power. 



NASSI'N^. A sub-family of the Mu- 

 ricidce, named from the typical genus 

 nassa. 



NATATO'RES {nato, to swim). An 

 order of Birds, easily distinguished by 

 their oar-like feet, adapted to swimming. 

 They include the duck, the gull, the 

 pelican, the diver, and the penguin. In 

 the first three, the length of the wings 

 adapts them for flight ; in the last two, 

 the wings are short, and serve only as 

 fins. 



NATI'CID^. The Nerits; a family 

 of the Phytophagous Gasteropods, in 

 which the spire is very small, but the 

 pillar is always thick ; the exposed part, 

 or inner lip, is often very broad; the 

 animal is slug-shaped. 



NATICI'N^. Sea-snails ; a sub- 

 family of the Naticidce, named from the 

 genus natica, and characterized by a 

 globose shell ; the inner lip is smooth, 

 not depressed. 



NATRIUM. A term formerly used 

 to designate sodium. Natron is native 

 carbonate of soda, found in mineral 

 seams or crusts, and hence called mineral 

 alkali. 



NA'TROLITE. A sub-species of 



