LIB 



LIB 



LEVER, in mechanics, an inflexible 

 right line, rod, or beam, supported in a 

 single point on a fulcrum or prop, and 

 used for the raising of weights ; being 

 either void of weight itself, or at least 

 having such a weight as may be commo- 

 diously counterbalanced. 



The lever is the first of those called 

 mechanical powers, or simple machines, 

 as being of all others the most simple; 

 and is chiefly applied for raising weights 

 to small heights. See MECHANICS. 



LEVISANUS, in botany, so called from 

 the Rev. Mr. Lewis, a genus of the Pen- 

 tandria Monogynia class and order. Es- 

 sential character : flowers aggregate ; ca- 

 lyx one-leafed, superior, five-cleft; corolla 

 five petalled, superior ; filaments inserted 

 into the base of the perianth ; styles two, 

 conjoined ; berry two celled ; seeds five 

 or six, compressed. There are five spe- 

 cies, which are all shrubs, and natives of 

 the Cape of Good Hope. 



LEYSERA, in botany, a genus of the 

 Syngenesia Polygamia Superflua class and 

 order. Natural order of Composite Dis- 

 coideae. Corymbiferze, Jussieu. Essen- 

 tial character : calyx scariose ; down chaf- 

 fy ; in the disk feathery also ; receptacle 

 subpaleaceous. There are three spe- 

 cies. 



LEY, or lees, a term usually applied to 

 any alkaline solution, made by levigating 

 any ashes that contain an alkali. Soap- 

 lees is an alkali used by soap-boilers, or 

 potash or soda in solution, and made caus- 

 tic by lime. Lees of wine are the refuse, 

 or sediment, that deposits from wine by 

 standing quiet. 



LEYDEN phial, in electricity, is a glass 

 phial or jar, coated both within and with- 

 out with tinfoil, or other conducting sub- 

 stance, that it may be charged, and em- 

 ployed in a variety of experiments. Flat 

 glass, or glass of any shape, may be used 

 in the same way. 



LIATRIS, in botany, a genus of the 

 Syngenesia Polygamia JBqualis class and 

 order. Natural order of Compositae Ca- 

 pitatse. Cinarocephalae, Jussieu. Essen- 

 tial character: calyx oblong, imbricate, 

 awnless, coloured ; down feathered, co- 

 loured ; receptacle naked, hollow, dotted. 

 There are eight species. 



LIBELLULA, in natural history, dra- 

 gon-fly, a genus of insects of the order 

 Neuroptera. Mouth armed with jaws, 

 more than two in number ; lip trifid ; an- 

 tennae very thin, filiform, and shorter 

 than the thorax ; wings expanded ; tail of 

 the male insect furnished with a forked 

 process. There are about sixty species, 



divided into two families. A. wings ex- 

 panded when at rest. B. wings erect 

 when at rest ; eyes distinct ; outer divi- 

 sions of the lip bifid. The whole tribe of 

 the libellula are remarkable for being ra- 

 venous : they are usually to be seen ho- 

 vering over stagnant waters, and may, in 

 the middle of the day, be observed fly- 

 ing with great rapidity in pursuit of the 

 smaller insects. These brilliant and beau- 

 tiful animals were once, and for a consi- 

 derable time, inhabitants of the water: in 

 that state, as larva, they are six-footed,, 

 active, and furnished with an articulate 

 forcipated mouth. They prey upon aqua- 

 tic insects, and the larva of others : the 

 pupa resembles the larva, but has the ru- 

 diments of wings. The most remarkable 

 of the English species is the L. varia, or 

 great variegated libellula, which makes its 

 appearance towards the decline of sum- 

 mer, and is an animal of singular beauty. 

 Its length is about three inches ; and the 

 wings, when expanded, measure nearly 

 four inches from tip to tip. The female 

 libellula drops her eggs in the water, 

 which, on account of their specific gra- 

 vity, sink to the bottom : after a certain 

 period they are hatched into larvae, hav- 

 ing a singular and disagreeable aspect : 

 they cast their skins several times before 

 they arrive at their full size, and are of a 

 dusky brown colour : the rudiments of 

 the future wings appear on the back of 

 such as are advanced to the pupa state in 

 the form of oblong scales, and the head 

 is armed with a singular organ for seizing 

 its prey. They continue in the larva 

 and pupa state two years ; when, having 

 attained to their full size, they prepare 

 for their ultimate change, and creeping 

 up the stem of some water plant, and 

 grasping it with their feet, they make an 

 effort, by which the skin of the back and 

 head is forced open, and the enclosed 

 libellula gradually emerges. This process 

 takes place in a morning, and during a 

 bright sunshine. The remainder of the 

 animal's life is short, the frosts of autumn 

 destroying them all. " It is impossible," 

 says Dr. Shaw, " not to be struck with 

 admiration on contemplating the changes 

 of the libellula, which, while an inhabi- 

 tant of the water, would perish by any 

 long exposure to the air, while the com- 

 plete animal, once escaped from the pu~ 

 pa, would as effectually be destroyed by 

 submersion under water, of which not an 

 hour before it was the legitimate inhabi- 

 tant." In this, and other species of the 

 libellula tribe, the structure of the eye is 

 deserving 1 of notice A common magni- 



