LIT 



LOG 



which have a stony axis, as distinguished 

 from the keratopliyta, or horny polyps. 



LITMUS. Turnsol. A blue pigment 

 obtained from the Lichen orcella, and 

 employed by chemists for detecting the 

 presence of an uncombined acid. Litmus 

 paper is prepared by digesting pow- 

 dered litmus in water, and painting 

 with it white paper which is free from 

 alum. 



LI'TUUS. The name given to a spiral 

 thus described :— Let a variable cir- 

 cular sector always have its centre at 

 one fixed point, and one of its termi- 

 nal radii in a given direction. Let the 

 area of the sector always remain the 

 same; then the extremity of the other 

 terminal radius describes the lituus. 

 The polar equation of this spiral is 

 r^e= a.— Pen. Cycl. 



LIVER-ORE. Hepatic mercurial ore. 

 A mixture of cinnabar with bituminous 

 and earthy particles, from Idria, compact 

 and slaty. 



LIVER-PYRITES. Sulphuret of iron, 

 of a radiated texture ; distinct from the 

 fer sulphur^ hepatique of some French 

 mineralogists, which consists of both ra- 

 diated and common iron-pyrites con- 

 verted into brown iron-stone. 



LIXIVIA'TION {lixivium, a ley). The 

 application of water to a saline body 

 which consists of both soluble and inso- 

 luble ingredients. The solution obtained 

 is the lixivium, or ley, — a term used by 

 the older chemists to signify a solution of 

 an alkali in water ; what is now called 

 an alkaline solution, being formerly 

 called an alkaline lixivium or ley. 



LLANDEILO FLAGS. The name of 

 one of the Lower Silurian Rocks, con- 

 sisting of a bed, 1200 feet in thickness, 

 of hard, dark-coloured, slaty sandstones, 

 frequently calcareous, sometimes slightly 

 micaceous, containing mollusca and tri- 

 lobites. 



LOADSTONE. An ore of iron which 

 possesses the peculiar properties of at- 

 tracting iron, and of turning towards the 

 north pole, when freely suspended. M. 

 Haiiy observes, that the ores in which 

 the iron contains the least oxygen inde- 

 pendently of other combinations, form 

 natural magnets ; and he terms the load- 

 stones of commerce, found in different 

 parts of the world, oxidulated iron. The 

 properties of the natural loadstone may 

 be communicated to iron and steel, which, 

 when properly prepared and touched by 

 the loadstone, are called artificial mag- 

 nets. See Magnet. 

 200 



LOAM. A soil consisting chiefly of 

 clay, silicious sand, and chalk, or car- 

 bonate of lime. The quality of a loamy 

 soil varies considerably with the relative 

 proportions of these constituents. 



LOAM or BRICK CLAY. A variety 

 of clay of variable appearance, its colour 

 depending on the proportion of oxide of 

 iron which it contains. It lies upon the 

 London clay, and contains a few organic 

 remains, sometimes the teeth of the ele- 

 phant. The Hedgerley loam, found near 

 Windsor, is used in making lutes, &c. 



LOBELIA'CE^. The Lobelia tribe 

 of dicotyledonous plants. Herbaceous 

 plants or shrubs, with leaves alternate ; 

 flowers axillary or terminal; stamens 

 syngenesious ; ovary inferior ; fruit cap- 

 sular. 



LO'BOITE. A magnesian idocrase 

 occurring in Norway. 



LOCOMO'TIVE (locus, place, moveo, 

 to move). A term generally expressive 

 of motion attended by a change of place, 

 and thus opposed to stationary: thus, a 

 locomotive power, or engine, is any power 

 or engine employed for transport, which 

 travels with the load it draws. 



LOCULICI'DAL {loculus, a cell, ccedo, 

 to cut). That mode of dehiscence of 

 fruits, in which the loculi, or cells, are 

 severed at their backs, as in lilac. The 

 older botanists described it as dehiscence 

 with the valves opposite to the dissepi- 

 ments. 



LO'CUS. The Latin word for a place. 

 In geometrical analysis, it denotes a line 

 or surface traversed by a point which va- 

 ries its position according to some deter- 

 minate law. 1. The locus of the vertex 

 of an isosceles triangle described upon a 

 given base, is the straight line which bi- 

 sects the base at right angles. 2. The 

 locus of the vertex of a triangle which 

 has a given base and a given area, is a 

 pair of straight lines parallel to, but on 

 different sides of, the base. 3. The lociis 

 of the vertex of a triangle which has a 

 given base and a given vertical angle, 

 and which lies on a given side of the 

 base, is an arc of a circle of which the 

 given base is the chord. 



1. Plane and Solid Loci. When the 

 locus of the variable point is a straight 

 line or a circle, it was called by the an- 

 cient geometers a plane locus ; when one 

 of the conic sections, a solid locus. 



2. Orders of Loci. Loci are distin- 

 guished into orders or degrees, according 

 to the dimensions of the algebraic equa- 

 tions by which they are represented. 



