LAP 



LAV 



uneven or conchoidal ; lustre feeble ; a ' 

 little translucent at its edges. It scratches j 

 glass, but gives sparks with steel with dif- \ 

 ficulty. Specific gravity about 2 '30. Its | 

 analysis is very differently given by differ- 

 ent authors. It contains silica, nearly 

 fifty per cent, carbonate of lime, alumina, 

 potash, soda, oxide of iron, and sulphuric 

 acid. It occurs associated with primary j 

 rocks, especially granite. It is accompa- | 

 nied by garnets, quartz, felspar, &c., with j 

 some of which it is often intermixed. It I 

 is found chiefly in China, Persia, and 

 Russia. It is capable of a high polish, 

 and is much esteemed. Its chief use, 

 however, is to furnish the ultra -marine 

 blue, used by painters, a pigment remark- 

 able for the durability of its colour. 



LA'PIS (ETI'TES. Eagle-stone. A mineral 

 which derives its name from the ancient 

 belief that it was found in the nests of the 

 eagle. It is a variety of iron ore, com- 

 monly met with in the argillaceous mines 

 of this country. Its supposed virtues are 

 described by Dioscorides, CEtius, and 

 Pliny, who assert that if tied to the arm it 

 will prevent abortion ; if fixed to the thigh 

 it will facilitate delivery. 



LA'RYNX. (XdpuyC, Gr.) The upper part 

 of the wind-pipe or trachea ; that cartila- 

 ginous projection in the throat known as 

 the pomum Adami, which strictly is formed 

 by one of the cartilages of the larynx only, 

 namely, the thyroid. The larynx consists 

 of five cartilages, the cricoid, thyroid, two 

 arytsenoid, and the epiglottis. 



_,A'TERAL. (lateralis, Lat. lateral, Fr. la- 

 terale, It.) Pertaining to the side ; ex- 

 tending to one side from the centre. 



LATERI'TIOUS. (lateritius, Lat.) Of the 

 colour of brick- dust; applied generally to 

 sediment. 



LATIRO'STROUS. (from latus, broad, and 

 rostrum, a beak, Lat.) Broad beaked. 



LA'TITUDE. (latitudo, Lat. latitude, Fr. 

 latitudine, It.) The latitude of a place 

 on the earth's surface is its angular dis- 

 tance from the equator, measured on its 

 own terrestrial meridian : it is reckoned 

 in degrees, minutes, and seconds, from 

 up to 90, and northwards or southwards 

 according to the hemisphere the plane 

 lies in. Thus the observatory at Green- 

 wich is situated in 51 28' 40" north lati- 

 tude. Latitude may also be thus defined, 

 the angular distance between the direction 

 of a plumb-line at any place and the plane 

 of the equator. 



LA'TROBITE. A mineral, thus named after 

 Latrobe, having been found by him on 

 the coast of Labrador. Colour, pale 

 pink; specific gravity 2 '8. Occurs mas- 

 sive and crystallized. 



LA'TTICED. In conchology, shells having 

 longitudinal lines or furrows decussated 



by transverse ones, resembling lattice- 

 work. 



LA'RVA. (larva, a mask, Lat.) An insect 

 in its caterpillar state, before it has at- 

 tained its winged or perfect state. Some 

 insects, as the butterfly, moth of the silk- 

 worm, &c., pass through four distinct 

 states, namely, the egg; the larva, or 

 caterpillar ; the pupa, or chrysalis ; and 

 the imago, or perfect insect. The egg, 

 which is deposited by the perfect insect, 

 gives birth to a caterpillar, or larva , an 

 animal, which, in outward shape, bears 

 not the slightest resemblance to its parent, 

 or to the form it is itself afterwards to 

 assume. It has, in fact, both the external 

 resemblance, and the mechanical struc- 

 ture, of a worm. The same elongated 

 cylindric shape, the same annular struc- 

 ture of the denser parts of the integument, 

 the same arrangements of longitudinal 

 and oblique muscles connecting these 

 rings, the same apparatus of short feet, 

 with claws, or bristles, or tufts of hair, 

 for facilitating progression ; in short, all 

 the circumstances most characteristic of 

 the vermiform type are equally exempli- 

 fied in the different tribes of caterpillars, 

 as in the proper annelida. These exter- 

 nal investments, which hide the real form 

 of the future animal, have been compared 

 to a mask ; so that the insect, while wear- 

 ing this disguise, has been termed larva, 

 the Latin name for a mask. Roget. 



We have in the larvae of insects a kind 

 of intermediate animal, in some degree 

 expansile. 



LA'VA. (This word, according to Kirwan, 

 is derived from the Gothic, lopa or lauffen, 

 to run, and is applied to the melted or li- 

 quified matter, discharged from the mouths 

 of volcanoes.) The matter which flows 

 in a fused, or melted, state from a vol- 

 cano. 



Lava, whatever be its chemical compo- 

 sition, puts on very different appearances, 

 according to the circumstances which ac- 

 company its consolidation, hence by some 

 authors it has been divided into compact 

 lava, cellular lava, and cavernous lava. 

 The mineral called felspar forms, in gene- 

 ral, more than half of the mass of modern 

 lavas. When this is in great excess, lavas 

 are called trachytic ; when, on the other 

 hand, augite prevails, they are called ba- 

 saltic. When lava is observed as near as 

 possible to the point whence it issues, it 

 is found to be, for the most part, a semi- 

 fluid mass of the consistence of honey, 

 but occasionally so liquid as to penetrate 

 the fibre of wood. It soon cools exter- 

 nally, arid consequently exhibits a rough 

 uneven surface ; but, from its being a bad 

 conductor of heat, the internal mass re- 

 mains liquid long after that portion which 



