LJBRATION OF THE EARTH LICHENS. 



others at 250,000 volumes, and 30,000 MSS.), and 

 the library of the British mu-eiimat London (180,000 

 books, and about 60,000 MSS.). Besides the Bibli- 

 othryuc tin rot, there are, in Paris, those of the 

 arsenal (150,000 printed books, 6000 MSS.), of St 

 Cfiirviere (1 10,000 printed books, 2000 MSS.); of 

 the institute (50,000 volumes); of the chamber of 

 deputies (40,000); the Maiarin library (90,000); 

 making in all, 1,200,000 volumes in the public 

 libraries in Paris. In the rest of France, there are 

 273 public libraries, the principal of which are those 

 of Lyons (containing together 600,000 volumes); 

 Bordeaux (105,000); Aix (73,000), &c. The total 

 number of volumes, in these provincial libraries, is 

 3,000,000. Access to these great collections is easily 

 obtained, both by natives and foreigners. In Italy, 

 there are a great number of valuable libraries, of 

 which that at Bologna, founded in 1650, contains 

 150,000 volumes, 9000 MSS.; the Magliabecchi 

 library at Florence, 150,000 volumes, 9000 MSS.; 

 the university library at Genoa, 70,000 volumes; the 

 Ambrosial) at Milan, 60,000 printed volumes, and, at 

 least, 15,000 MSS. according to others, 140,000 

 volumes, and 15,000 MSS.; that at Modena, 80,000 

 % olumes, and that of Naples 130,000. The Vatican 

 1 brary is very large and famous, but in much dis- 

 order. The number of books in foreign libraries is 

 very difficult to be ascertained with precision, and 

 the statements differ so much, that the above estimates 

 are, in many cases, little better than approximations. 

 In the United States of America, the principal 

 libraries are that of Harvard college (36,000 volumes); 

 of the Boston Athenaeum (26,000 volumes); of the 

 Philadelphia library (27,000 volumes); of congress 

 (16,000 volumes); of Charleston (13,000). 



LIBRATION OF THE EARTH is sometimes 

 used to denote the parallelism of the earth's axis in 

 every part of its revolution round the sun. 



LIBRATION OF THE MOON. Very nearly the 

 same face of the moon is always turned towards the 

 earth, it being subject to only a small change within 

 certain limits, the spots near the edge appearing 

 and disappearing by turns; this is called its libration. 

 The moon turns about its axis in the same direction 

 in which it revolves in its orbit. Now, the angular 

 velocity about its axis is uniform, and it turns about 

 its axis in the same time in which it makes a complete 

 revolution in its orbit ; if, therefore, the angular 

 motion about the earth were also uniform, the same 

 face of the moon would always be turned towards 

 the earth; for, if the moon had no rotation on her 

 axis, when she is on opposite sides of the earth, she 

 would show different faces; but if, after she has made 

 halt' a revolution in her orbit, she has also turned 

 half round her axis, then the face, which would 

 otherwise have been shown, will be turned behind, 

 and the same face will appear ; and thus, if the 

 moon's angular velocity about her axis were always 

 equal to her angular velocity in her orbit about the 

 car Ui, the same side of the moon would be always 

 towards the earth; but as the moon's angular velocity 

 about her axis is uniform, and her angular velocity 

 in her orbit is not uniform, these angular velocities 

 cannot continue always equal, and therefore the moon 

 will sometimes show a little more of her eastern 

 parts, and sometimes a little more of her western 

 parts. This is called a libration in longitude. Also 

 the moon's axis is not perpendicular to the plane of 

 her orbit, and, therefore, at opposite points of her 

 orbit, her opposite poles are turned towards the 

 earth; therefore her poles appear and disappear by 

 turns. This is called a libration in latitude. Hence 

 nearly one half of the moon is never visible at the 

 earth, and therefore nearly one half of its inhabitants 

 (if it have any) never see the earth, and nearly the 



other half never lose sight of it. Also, the time of 

 its rotation about its axis being a month, the length 

 of the lunar days and nights will be about a fortnight 

 each. It is a very extraordinary circumstance, that 

 the time of the moon's revolution about her axis 

 should he equal to that in her orbit. 



LIBYA, with the ancient geographers; a large 

 part of the north of Africa, west of JEgypt, which 

 was divided into Libya exterior and interior; some- 

 times also into Libya Proper, Lybia Marmarica, and 

 Lybia Cyrenaica. The Greek authors sometimes 

 comprehended all Africa under this name. 



LICENSES, or FREE LETTERS, were instru- 

 ments used to diminish the effect of the Berlin and 

 Milan decrees of Napoleon, and the British orders 

 in council, which threatened the destruction of 

 European commerce, if some exceptions had not 

 been made by both nations. Britain decreed first, 

 in November, 1808, that vessels of all nations, the 

 French excepted, might be provided with licenses, 

 good for one year, upon condition of importing grain 

 into Britain ; but, after 1809, licenses were given 

 under the condition of exporting British manufac- 

 tures or colonial produce. Licenses were also sold 

 by France, especially for the purpose of supplying 

 her navy. False papers for ships were also in com- 

 mon use. At last, it was decided by Britain to 

 grant licenses to all ships not French, even though 

 they carried a French license, upon condition that 

 one third part of the cargo should be British goods, 

 the same portion of French cargo being also allowed. 

 France also gave licenses (to American vessels) to 

 export French goods, and, in return, to import colo- 

 nial produce. Licenses were granted by Russia for 

 trade with Britain, from 1811, and by Sweden, for 

 the same trade, from 1812; but, at the fall of the 

 famous continental system (see that article),' the 

 licenses became useless. 



LICENTIATE ; an academical dignity between 

 the baccalaureate and the doctorate, and the obtain- 

 ing of which is a necessary step to taking the doctor's 

 degree. Licentiate also signifies the person who has 

 received the degree. A licentiate in theology has 

 the right of delivering theological lectures, and a 

 licentiate in medicine the right to practise. 



LICHENS ; a family of plants, belonging to the 

 Linnaean class cryptogamia, containing about 1200 

 known species, which are now arranged under seve- 

 ral genera. Their substance is powdery, crustaceons, 

 membranous, coriaceous, or even corneous; and their 

 form that of a horizontal frond, sinuated, lobed, or 

 divided, bearing scattered tubercles and cup-like 

 warts, or branching and coralloid. They are com- 

 mon every where, adhering to rocks, the trunks of 

 trees, and barren soil. On ascending mountains, 

 they are found flourishing beyond the limit of all 

 other plants, even to the very verge of perpetual 

 snow. Many of them, fixing upon the hardest rocks, 

 by retaining moisture, facilitate their decomposition, 

 and promote the formation of soil. They are gener- 

 ally perennial, and grow by receiving moisture 

 through all parts of their surface, and, though fre- 

 quently desiccated, the least rain restores their fresh- 

 ness. Many of the species appear to be universally 

 distributed, occurring in all parts of the globe ; but 

 the lichens of the equatorial regions and southern 

 hemisphere have not, hitherto, been satisfactorily 

 examined. Several of the species are used for suste- 

 nance in time of scarcity, by the inhabitants of the 

 northern regions. The tripe de roche of the Cana- 

 dians, so often resorted to by the fur traders, is also 

 a lichen, somewhat resembling the substance from 

 which the name is derived. The reindeer moss (cce- 

 nomyce rangiferina) is common, in sterile soil, in 

 many parts of the northern hemisphere ; but, in the 



