LEV 



LIB 



LEVEL. Two points on the surface 

 of the earth are said to be on the same 

 level, where they are equally distant from 

 the earth's centre. A level surface, there- 

 fore, is not a plane, but a portion of a 

 spherical surface; and this is the form 

 which a sheet of water, or any other 

 liquid, naturally assumes. 



Horizordal and dead level. There are 

 various instruments used in levelling, 

 ■which are called levels. These all give a 

 horizontal level, that is, a tangent to the 

 earth's surface ; and in the case of a 

 drain or canal, the bottom of the exca- 

 vation must be carried lower than the 

 level indicates, otherwise the water would 

 not run. The declivity must be in a 

 circle equivalent to that of the earth's 

 circumference before the water could 

 reach it, and this would then be termed 

 a dead level. 



LE'VER {levo, to raise). A physical 

 or compound lever is any inflexible rod or 

 solid body whatever, supported on one 

 point, and acted on at two other points, 

 by two forces tending to move it in oppo- 

 site directions about the point of support. 

 The two forces acting on the lever are 

 called the power and the weight, and the 

 point on which the lever is supported, or 

 about which it turns, is called the ful- 

 crum. The power of this instrument 

 depends on the proportion between the 

 lengths of the parts of the lever on each 

 side of the fulcrum. 



1. Lever, one, or two-armed. 1. In the 

 one-armed lever, the power and the 

 weight are both on one side of the ful- 

 crum, as in the common wheel-barrow. 

 2. In the two-armed lever, the fulcrum 

 is between the power and the weight, 

 being either equidistant from the two 

 forces, or nearer to one of the forces than 

 to the other. 



2. Levers are rectilinear or curvilinear, 

 according as their arms are straight or 

 curved lines. A lever is angular, when 

 the arms form an angle, in which case 

 the fulcrum is at the vertex of the 

 angle. 



3. Lever, Universal. An instrument 

 constructed by combining the lever with 

 the wheel and axle; its object is to give 

 a continued rectilinear motion to a heavy 

 body, by means of the reciprocating 

 motion of the lever. 



LEVIGATION {IcBvigo, to polish ; 

 from IcBvis, smooth). The process of 

 rubbing earths and some metallic sub- 

 stances with a muller upon a flat table 

 of hard stone. Some fluid is added to 

 196 



assist the operation, and in this respect 

 it differs from trituration. 



LE'VINE. A scarce zeolitic sub- 

 stance, occurring in the cavities of an 

 amygdaloid rock, at Dalsnypen in Faroe. 



LEY. Lixivium. A technical term 

 for a solution of alkali in water. 



LEYDEN JAR. An apparatus for 

 accumulating and condensing electricity, 

 constructed on the principle that the oppo- 

 site electricities may be held in a latent 

 state. It consists of a cylindrical glass- 

 jar coated to a certain height, inside and 

 outside, with tinfoil, so that every point 

 of both sides of the glass may be brought 

 into communication at the same moment. 

 To convey the fluid to the interior of the 

 jar, a brass wire runs through its lid, the 

 upper end terminating in a ball, and the 

 lower end, divided into several fine points, 

 touches the foil within the jar. A com- 

 bination of such jars is called an electri- 

 cal battery. 



LHE'RZOLITE. A mineral consist- 

 ing of coccolite mixed with serpentine. 



LIAS. A subdivision of the Oolitic or 

 Jurassic system of Geology, consisting of 

 a great argillaceous deposit with some 

 thick arenaceous bands, and many con- 

 cretions and beds of argillaceous lime- 

 stone. It is continued without interrup- 

 tion from the coast of Dorsetshire to the 

 north-east coast of Yorkshire. The term 

 lias is supposed to be derived from the 

 appearance of the bed in riband-like 

 layers of different colours, observed in 

 some parts of England. 



LIBELLU'LIDiE {libellula, the dra- 

 gon-fly). A group of neuropterous in- 

 sects, which are aquatic in their prepa- 

 ratory states, and emerge from the water 

 at the period of their final metamor- 

 phosis. 



LIBER. The inner bark of a tree, 

 used instead of paper by the ancients to 

 write upon. In botanical language, it 

 denotes the interior fibrous portion of the 

 bark, lying immediately upon the albur- 

 num ; the endophloeum of later writers. 

 See Bark. 



LIBRA. The Balance; the seventh 

 of the zodiacal constellations, consisting 

 of fifty-one stars, the principal of which 

 is Zubenich Meli. It denotes the first 

 month of spring, and extends from the 

 20th of March to the 20th of April. This 

 month answers to the vernal equinox 

 and the equality, or balance, of the days 

 and nights. 



LIBRA'TION {libro, to balance). A 

 slight swaying motion, like that of a 



