LEV 



Lie 



zontal position by the assistance of 

 a a, whicii is upt)n a moveable pivot, 

 made by one oi the screw nails at k. 

 The distance of « a from i i is imma- 

 terial. A small stop is fastened at 

 the back of b b, for tlie purpose of 

 preventing c f from falling below c d. 

 The rise of a road is shown by look- 

 ing from e towards /; the fall of a 

 road, of course, by looking from /to- 

 wards e, and, if great correctness is 

 required, the observation should be 

 reversed " 



LEVELLING. The art of discov- 

 ering the level of surfaces, or how 

 high one place is above another ; jt 

 also means, in agriculture, the reduc- 

 tion of hills or mounds to a level or 

 plain surface, which is done by the 

 plough, or tlie machine figured under 

 the article Barren Soil. 



The level set on a rod (Fig. 1) in 

 the preceding article is all that is ne- 

 cessary for short distances ; but tel- 

 escopes are used in extensive sur- 

 veys. 



LEVELLING STAVES. Straight 

 rods, six or more feet high, and divi- 

 ded into marks at the inches, which 

 can be distinctly seen at a short dis- 

 tance ; in more delicate observations 

 the staff carries a moveable sight 

 with a central mark, which is adjust- 

 ed by an assistant, according to the 

 signs of the surveyor, until the level 

 line is reached. 



LEVER. An inflexible bar capa- 

 ble of moving around a prop or ful- 

 crum : the advantage, or leverage, 

 gained depends on the distance at 

 which the power acts from the prop, 

 and weight or resistance. The lever 

 is not only the simplest, but the only 

 true mechanical power. Writers 

 speak of levers of the first, second, 

 and third kinds : in the first, the ful- 

 crum is between the power and 

 weight ; in the second, the fulcrum 

 is at one end and the power at the 

 other, the weight being between 

 them ; in the third, the fulcrum and 

 weight are at the ends, the power 

 intermediate ; in this case there is 

 loss of power, but gain in the rapidi- 

 ty of movement of the weight : the 

 treadle of a lathe is an instance. 

 468 



f LEVERAGE. The advantage 

 gained in power by using a lever. 

 j LEVERET. A young hare. 

 I LEVIGATION. The reduction of 

 a solid to an impalpable powder with 

 the assistance of water or other 

 fluids ; this may be done in a mortar 

 or on a slab ; the mixture is after- 

 ward diffused in water, and the light 

 parts, which remain suspended some 

 seconds, poured off and retained, the 

 heavier portions being again tritu- 

 rated. 



LEY. Grass land. 



LEYDEN JAR. See Electricity. 



LIAS. An argillaceous limestone 

 of the secondary rocks ; abundant in 

 Europe, but unknown in the United 

 States. 



LIBELLULINES. A tribe of neu- 

 ropterous insects like the dragon-fly, 

 which are found about water, and 

 prey on other insects. The word Li- 

 bcllula designates a genus of this 

 family. 



LIBER. The innermost bark of 

 trees. 



LICE ON ANIMALS. Nearly all 

 animals are subject to some of these 

 parasites : they are produced from 

 filth,confinement, herding with infest- 

 ed animals ; the creatures affected he- 

 come restless, rub themselves against 

 posts, bite the accessible parts of 

 their skin, and even become subject 

 to skin diseases. The best remedies 

 are, access to water, washing, comb- 

 ing, or currying the hide, anointing 

 with sulphur, mercurial, or whale oil 

 ointment ; decoctions of tobacco, and 

 other narcotic weeds, are also valu- 

 able. 



LICE ON PLANTS. See Aphides. 



LICHENIN. The starchy matter 

 of lichens. 



LICHENS. " Plants of a very low 

 organization, which grow on the bark 

 of trees or rocks, when they form a 

 kind of incrustation, or upon the 

 ground, when they consist of irregu- 

 lar lobes, parallel with the earth's 

 surface. Occasionally, in all situa- 

 tions, they are found in a branched 

 state ; but their subdivisions are gen- 

 erally irregular, and without order. 

 Their fructification consists of hard 



