LUN 



MAC 



of the calendar, it is generally called a 

 lunation. 



LUNE (luna, the moon). Lunule. 

 The spherical surface included between 

 two semicircles ; or, the figure described 

 on a sphere or on a plane by two arcs of 

 circles which enclose a space. 



LU'NULITES {lunula, a little moon, 

 \i6oi, a stone). A genus of fossil cella- 

 riadce, consisting of animals (unknown) 

 contained in cellules, and arranged in 

 single tiers, so as to form orbicular poly- 

 paria. 



LUPUS. The Wolf; a southern con- 

 stellation, consisting of twenty -four stars, 

 and represented in maps as a wolf trans- 

 fixed by the spear of the Centaur. It is 

 situated directly beneath Scorpius. 



LUSTRE of ROCKS. This is one of 

 the distinguishing characters of rocks. 

 According to Mac CuUoch, the highest de- 

 gree of lustre is the plumbaginous, or 

 that of graphite or black lead, which is 

 seen in some clay-slates. The other ex- 

 treme is that of chalk, which Is dull, or 

 almost destitute of lustre. The principal 

 intermediate kinds are the silky, resin- 

 ous, vitreous, flinty, and waxy. 



LUTE. A compound paste, made of 

 clay, sand, &c., for closing retorts and 

 receivers, in order to render them air- 

 tight. 



LYCOPODIA'CEiE. The Club-moss 

 tribe of flowerless plants, characterized 

 by their creeping stems, the axis abound- 

 ing in annular ducts. Reproductive or- 

 gans are axillary sessile thecae, containing 

 either minute powdery matter, or sporules 

 marked at the apex with three minute 

 ridges. 



LYCO'PODITES. A general term for 

 those fossil plants which correspond in 

 some of their characters with some of the 

 genera composing the Lycopodiaceae. 



LYDIAN STONE. Flinty slate; a 

 kind of quartz or flint, allied to horn- 

 stone, but of a greyish black colour. . 



LYE or LEY. A solution of potass, or 

 other alkaline substance, used in the 

 arts. See Lixiviation. 



LYMPH {lympha, water). A colour- 

 less liquid which moistens the surface of 

 cellular membrane. The lymph of plants 

 is the unelaborated sap, so called from 

 its resemblance to water. 



M 



MAASTRICHT ROCKS. These rocks 

 are considered by geologists as an upper 

 part of the chalk formation ; and their 

 place in the scale of strata is in imme- 

 diate superposition above the chalk of 

 England, and at some small interval be- 

 low the calcaire grossier of the Paris 

 basin. 



MACE. The external envelope of the 

 seed of the myristica moschata, affording 

 an interesting example of an arillus, or 

 expansion of the placenta. 



MACERA'TION (macero, to make 

 soft by steeping). The steeping of ani- 

 mal or vegetable substances in a cold 

 liquid, for the purpose of softening the 

 parts previously to distillation, or for 

 that of dissolving their aromatic prin- 

 ciples. 



MA'CHINA PNEUMA'TICA. The 

 Pneumatic Machine ; a modern southern 

 constellation, consisting of three stars. 



MACHINE {machina, a frame or con- 

 trivance). Any instrument by which 

 power, motion, or velocity, is applied or 

 regulated. The force which puts a ma- 

 chine in motion is called the first or 

 prime mover. The point at which that 

 204 



force is applied is the acting point; and 

 that at which the effect is produced is 

 the working point; the machine being 

 the medium through which the power is 

 transferred, and by which it is modified 

 so as to answer the intended purpose. 

 When a simple body is the medium be- 

 tween the acting and the working points, 

 it is an instrument. 



MACI'GNO. The Italian term for a 

 hard siliceous sandstone, sometimes con- 

 taining calcareous grains, mica, &c. 



MA'CLE. Chiastolite. A mineral found 

 imbedded in clay-slate, in the Pyrenees, 

 and consisting principally of silica and 

 alumina. 



MACLU'REITE. Chondrodite or bru- 

 cite. A mineral substance consisting of 

 a silicate of magnesia with other matters, 

 occurring in New Jersey and at Pargas 

 in Finland, and named after Dr. Maclure. 



MACQUER'S SALT. Neutral arseni- 

 cal salt ; super-arseniate of potass. 



MACROCE'PHALOUS {^laKp69, large, 

 Ke(pa\T], the head). Large-headed; a 

 term applied by Richard to those dico- 

 tyledonous embryos, in which the two 

 cotyledons cohere, as in horse-chestnut. 



