Narrative of the Eddystone Lighthouse, 1793; | nitrogen of the air when heated to incandesStevenson's Account of the Bell Rock Light- cence. [ELECTRICITY.] house, 1824; Id. British Pharos, 1831; Lightning Conductor. The early reBrewster's Treatise on Burning Instruments, searches of electricians demonstrated that the 1812; The Lighthouses of the British Islands, effects produced by the passage of lightning 1836; Report of the Select Committee of the through different substances varied greatly House of Commons on Lighthouses, 1839; Re- according to the nature of the substance traport to the Commissioners of the Northern versed. Thus, its passage through a good Lighthouses, by A. Stevenson, 1834; and On conductor, such as a bar of metal, of sufficient the Inchkeith Dioptric Light, 1836; Belidor, sectional area, was found to produce only a Architecture Hydraulique, tome iv.; Peclet, slight elevation of temperature in the metal, Traité d'Éclairage, Paris 1827; Fresnel, Mé- whilst on the other hand its transit through moire sur un Nouveau Système d'Éclairage imperfect conductors, such as wood, stone, &c., des Phares, 1822; A. Fresnel, Description was attended with great heat and destructive Sommaire des Phares et Fanaux allumés sur mechanical effects, by which such imperfect les Côtes de France, 1837; Faraday On the conductors were torn to pieces, and, if comApplication of the Electric Light to Light-bustible, ignited. This knowledge of the effects houses,' Proceedings of the Royal Institution, of the disruptive electric discharge led to the vol. iii. p. 220; Frankland 'On Artificial Illumination,' Proceedings of the Royal Institution, vol. iv. p. 16.

Lightning. An electric phenomenon, produced by the passage of electricity between one cloud and another, or between a cloud and the

earth.

The identity of lightning with electricity, though it had been previously suspected, was first directly demonstrated by the celebrated Dr. Franklin, in the year 1749, by the experiment of drawing sparks from the string of the electric kite. Since that time the science of electricity has been greatly advanced; nevertheless, the cause of some of the appearances connected with lightning is not well explained even at the present day.

The phenomenon of lightning is exhibited ander two forms called respectively forked lightning and sheet lightning. The lightning is forked when the electric discharge occurs within a few miles of the earth's surface, and when it is directly seen by the observer. When, however, the discharge takes place below the horizon, or behind a dense cloud, only the scattered light reflected from the surfaces of the clouds illumined by the flash reaches the eye of the observer; the actual flash is not seen, but only the general illumination of a portion of the heavens. Such lightning is termed sheet lightning; and when the discharge takes place below the horizon or behind a very remote cloud, the distance is too great for the accompanying thunder to be heard. Sheet lightning may also sometimes be due to the electric discharges taking place at great elevations above the earth's surface. The more rarefied the air through which the electric spark passes, the less narrow and defined is its path. When the rarefaction is extreme, the discharge assumes the character of the aurora borealis; but in somewhat more dense regions of the atmosphere its appearance would resemble that of the peculiar kind of sheet lightning which is observed when the sky is free from clouds. Forked lightning is produced by the intense ignition of the particles of air lying in the path of this electric discharge, and is generally of a reddish tint, which is due to the pink light emitted by the

invention and adoption of the lightning conductor, which consists of a rod of metal, or series of rods placed in metallic contact, and extending from the earth to some distance above the highest point of the building or ship which it is designed to protect. The upper extremity of the conductor should be pointed, in order to convert, as far as possible, the ordinary spark or globular discharge into the less instantaneous brush discharge, and every prominent angle of the roof of a building should be furnished with its own pointed rod carefully connected with the main rod which descends to the earth. The latter should have its lower extremity carried to some distance from the foundations of the building, and low enough to reach moist earth; or, better still, it may be connected with a gas or water main. According to Sir J. Snow Harris, a copper rod threequarters of an inch in diameter is a sufficient and safe conductor for any stroke of lightning ever recorded. Usually a much smaller rod would doubtless suffice.

Lign Aloes (Lat. lignum aloës, the wood of the aloe). The fragrant wood of Aloexylum Agallochum.

Ligneous (Lat. lignum). In Entomology, a part is so called when it is composed of a hard inelastic substance like wood.

Lignin (Lat. lignum). This term has been applied to the pure woody fibre: it has also been called cellulose: its ultimate composition is represented by CHO,, but a higher equivalent is better adapted to its combinations, and its most convenient formula is C12H20010; it belongs, therefore, to the class of compounds of carbon and water which includes starch, gum, sugar, and some other substances. The ordinary varieties of woody matter differ in colour and texture; but when freed from foreign matters, they leave a white translucent residue, insoluble in water, alcohol, and ether, and convertible, by sulphuric acid, into a substance having some of the characters of starch, and then into dextrine and sugar. Certain piths, linen, cotton, paper, and some other allied substances, are nearly pure cellulose. Weak acids and alkaline liquids, and a weak solution of chlorine, have scarcely any action on it, but they change,

innumerable varieties. Some Liliaceous plants secrete stimulating principles, which, in diffe[(x − a)2 + y2 — a2 — 2!3]2 = 463 (b + 2 x ), rent degrees of concentration, give their activity whence we learn that the curve has a double to onions, garlic, chives, and similar garden point at the origin, two cusps at the circular productions, and medical value to squills. Liliaceous. In Botany, a term invented points at infinity, a double tangent parallel to b2 by Link to denote a corolla the petals of which the ordinate axis at the distance- from the have their ungues gradually dilating into a limb, and standing side by side. It is rarely also to the class of Cartesian ovals, and includes origin, and two points of inflexion. It belongs employed. the cardioid as a particular case corresponding to b=a. Just as the latter curve can be

2a

be generated as an epitrochoid, the rolling circle being taken equal to the fixed one.

Lilium (Lat.; Gr. λeípiov). A genus of Liliaceae consisting of numerous beautiful flowers, which are great favourites in gardens. generated as an epicycloid, so the limaçon may They are commonly called Lilies, and offer considerable variety of appearance. Several beautiful kinds are natives of Japan, the most glorious being L. auratum, with enormous white flowers spotted with rich red brown, and marked down each segment by a broad golden band. Some, as L. eximium, have long horizontal trumpet-shaped flowers; others, as the well-known White Lily, L. candidum, have the tube shorter, and the segments more rolled out; while others again, as L. Martagon, the Turk's Cap Lily, have the segments completely reflexed. In some countries the bulbous roots

are eaten.

Lillite. A silicate of iron found at Przibram in Bohemia. It resembles Glauconite in appearance, and is probably a product of the decomposition of Iron Pyrites.

Lima (Lat. a file). A genus of Lamellibranchiate Bivalves, of the tribe Ostracce, characterised by the length of their shells as compared with those of the nearly allied genus Pecten, and their more regular oval form. The ridges of the shell are most of them relieved with scales. The Lime swim with rapidity by means of their valves, but in a young state they secure themselves by means of a byssus.

Limacidae. [LIMAX.]

Limacina (Lat. limax, a slug). A genus of Testaceous Pteropodous Molluscs, existing in considerable numbers in the northern seas, and forming, with the Clio borealis and other small marine animals, the food of the whalebone whale. The body terminates in a spirally convoluted tail, and is lodged in a very thin shell, formed by one whorl and a half, umbilicated on one side and flattened on the other. The animal uses its light shell as a boat, and its wing-like fins as oars, and thus navigates in countless fleets the surface of the tranquil deep. Limaçon (Fr.). This name appears to have been given by Pascal to a certain curve of the fourth order and sixth class, whose form somewhat resembles a shell. It is generated from a circle by adding to and subtracting from all radii vectores through a point of its circumference a given constant. length. Its polar equation, therefore, if a denote the radius of the circle and 26 the length added and deducted, is

r=2(a cos 0+b).

The orifice of re

Limax (Lat. a slug). The name of a genus of the Linnæan Vermes Mollusca, of which the common slug is the type. The genus enters into the class Gasteropoda and order Pulmonaria of the system of Cuvier; and is now raised to the rank of a family (Limacide), which includes Limax proper; Arion, Fér.; Incilaria, Benson; Testacella, Lam.; Parmacella, Cuv. &c. Each of these genera has a small scutiform rudimentai shell developed in the substance of the mantle, and protecting the heart. spiration in the true slugs (Limax, Cuv.) is on the right side, and not so far forward as in Arion. The rudimental shell is marked with fine and concentric striæ, and is calcified internally. The species of this genus are the pests of gardens and cultivated grounds. Young plants may be protected from slugs by having a coarse horsehair rope coiled round their stems, or by being plentifully sprinkled with soot; or they may be watered morning and evening with strong and fresh lime water.

Limb. In Astronomy, the border or outermost edge of the sun, moon, or of a planet. Also the graduated edge of a circle, or other astronomical instrument.

In

Limb or Limbus (Lat. a border). Botany, a term applied to petals, to denote that portion which is supported by the unguis or claw; it is the same organ in a petal as the lamina in a leaf, and is what constitutes the broad thin coloured part which renders many flowers so beautiful.

Limbelite. An altered form of Chrysolite, occurring in small wax or honey yellow masses, in the basalt of Limbourg.

Limber (of uncertain derivation; possibly connected with limp, Swiss lampen, to hang loose: Wedgwood). În Artillery, a two-wheeled carriage, carrying ammunition boxes, to which the trail of the gun carriage is attached, when the latter has to be moved. It thus forms with the gun carriage a four-wheeled carriage. To limber up is to attach the gun to the limber.

Limber Strakes. The planking of a ship's internal skin, above the floor timbers, and next, horizontally, to the limbers. They are among the thickest of the planks used.

Limbers. In Shipbuilding, the main drains of the vessel. They are gutters running along In rectangular coordinates, its equation may be each side of the keelson, receiving the hose of and all the internal drainage of the

written in the form

the pumps,

vessel. They are emptied from time to time by colours, and has an acrid taste. It absorbs carthe pumps. bonic anhydride by exposure to air; and as carLimbo (Lat. limbus, a hem or edge). Abonate of calcium is insoluble in water, it beregion supposed by some of the schoolmen to comes milky in consequence; so that lime-water is lie on the edge or neighbourhood of hell. This a useful test of the presence of carbonic anhydride. served as a receptacle for the souls of just men, The nature of lime was first demonstrated by not admitted into purgatory or heaven. Such Davy in 1807: he showed that, like the other were, according to some Christian writers, the alkalies, it was a metallic oxide. The metallic patriarchs and other pious ancients who died base of lime has been termed calcium: its equibefore the birth of Christ: hence the limbo valent is 40, and lime, being a compound of one was called limbus patrum. These, it was atom of calcium and one of oxygen (CaO), is believed, would be liberated at Christ's second represented by the equivalent 56; and hydrate coming, and admitted to the privileges of the of lime by 56 lime + 18 water = 74. blessed in heaven. This latter idea is probably The salts of calcium are generally obtained an adorned representation of the remarkable by dissolving carbonate of calcium in the passage in St. Peter's Epistle (1 iii. 19), where respective acids: several of them exist native. he says that Christ preached to the spirits in Sulphate of calcium (Ca,SO) (anhydrite, prison; and being held by certain of the later alabaster, selenite, or gypsum) is an abunfathers, seems to have given some influence to dant natural product, and may be formed the growing opinion in favour of a purgatory. artificially by adding sulphuric acid, or the Dante has fixed his limbo, in which the dis- soluble sulphates to solutions of the salts of tinguished spirits of antiquity are confined, as lime. Its crystals include two atoms of the outermost of the circle of his hell. The use water. When these crystallised sulphates of which Milton has made of the same superstitious calcium are heated, they part with their water belief is well known. (Paradise Lost, book iii.) and fall into a white powder, called plaster of The analogous term, limbus puerorum, was Paris; when this is mixed with water it again applied to the abode of children dying un- combines with it, and concretes into a white baptised before the commission of mortal sin. mass; hence its use for casts, busts, &c. SulIt is described as a neutral state, without actual phate of calcium is often contained in spring happiness or torment. Some of the fathers water, which is thus rendered hard and unfit held, however, a less merciful doctrine. In one for washing. These waters become turbid upon of his sermons against Pelagius, Augustine the addition of a spirituous solution of soap. declared that such infants descended into everlasting fire, while Fulgentius maintained that even children dying before birth must be punished by the eternal torture of undying fire. (Lecky, Hist. of Rationalism in Europe i. 397.) Lime (Ger. leim, glue). This very useful earth is obtained by exposing chalk and other kinds of limestone, or carbonates of calcium, to a red heat-an operation generally conducted in kilns constructed for the purpose; the carbonic anhydride is thus expelled, and lime, more or less pure, according to the original quality of the limestone, remains. In this state it is usually called quicklime. Its specific gravity is about 3. When sprinkled with water it becomes very hot, and crumbles down into a dry powder, called slaked lime or hydrate of lime. When exposed for some weeks to the air, it also falls into powder, in consequence of the absorption of moisture and of a portion of carbonic anhydride from the atmosphere; so that, in this case, part of the lime gradually reverts to the state of carbonate, and loses its causticity.

Pure lime may be obtained by heating pow'dered Carrara marble to whiteness in an open crucible. It is white, very infusible, but promotes the fusion of some other earths and oxides, and is therefore used as a a flux in several metallurgic processes. It is highly luminous when intensely heated, as for instance by the oxy-hydrogen blowpipe. [DRUMMOND'S LIGHT.] Lime is soluble in about 700 parts of water, and is somewhat more soluble in cold than in hot water. But, weak as this solution is, its action is powerfully alkaline upon vegetable

Phosphate of calcium (Ca,P,O,) is found native, constituting the mineral called apatite. The earth of bones is also chiefly a similar phosphate of lime. Oxalate of calcium is very insoluble, and is precipitated whenever oxalic acid or a solution of an oxalate is added to solutions containing lime; hence it is that oxalate of ammonium is so valuable a test of the presence of linie, and is frequently used for the purpose of separating lime in analysis. When oxalate of calcium is well dried, at 500°, it is anhydrous, and consists of 40 calcium, 24 carbon, and 64 oxygen = 128. This substance is occasionally found in the human urine, and sometimes forms calculi: these are often of a reddish brown colour and a rough exterior, whence they have been termed mulberry calculi. When hydrate of lime is exposed to chlorine, the gas is absorbed, and a chloride of lime is obtained. This article is manufactured upon an extensive scale, under the name of bleaching powder, and contains about 33 per cent. of chlorine available for bleaching purposes. It evolves chlorine when acted upon by acids; and gives it out very slowly when exposed to air, in consequence of the absorption of carbonic anhydride. It is a most useful disinfecting material, and when dissolved in water forms bleaching liquid. Carbonate of calcium (CaCO,) is thrown down when alkaline carbonates are added to solutions of the salts of calcium. It is a most abundant natural product, and is found pure in the varieties of calcareous spar and statuary marble. Chalk and several varieties of limestone are also nearly pure carbonates of calcium. It is easily

distinguished from other minerals by effer- Lime Light. [DRUMMOND'S LIGHT.] vescing in dilute acids and by yielding quick- Limestone. Stone consisting chiefly of lime when a fragment is heated before the uncrystallised carbonate of calcium. Perfectly blowpipe. It is constituted of 56 lime +44 crystallised carbonate of calcium is calc spar or carbonic anhydride: the equivalent, therefore, Iceland spar. Imperfectly crystallised carboof carbonate of calcium is 100. [LIMESTONE.] nate of calcium with a fine grain, or with the The uses of lime are very numerous. Its texture of sugar, is called MARBLE. Carbonates most important application is in the manu- of calcium and magnesium are described as facture of mortar and other cements used in MAGNESIAN LIMESTONES. building. It is also very extensively used as a manure to fertilise land.

LIME (so called from the glutinous juice of the young shoots: the word is the same as Ger. leim, Lat. limus, Eng. slime and loam). The name of the Linden-tree, Tilia europea, which, however, is by some authors said to be more correctly Line-tree, from its bark or bast being used to make cordage. The name is also applied to certain fruits of the Citrus family, related to lemons and citrons. The varieties of Citrus Limetta are called sweet limes; and some varieties of the lemon, C. Limonium, are also popularly called limes. The fruit, like that of the lemon, is used for its acid juice.

Compact limestone is sometimes white and nearly pure, sometimes coloured with iron or other metallic oxides, and often mixed irregularly with clay and sand. It passes by insensible gradations into impure limestone, marlstone, calcareous clay, and marl.

Limestones of all kinds are found in rocks of all geological ages; but it is generally fancied that the more crystalline varieties occur with the more ancient or the more distinctly metamorphic rocks. Thus in England the carboniferous limestones pass into marble. In the Alps, however, the oolitic rocks, and in the Carpathians cretaceous rocks, assume this form, and not unfrequently even tertiary rocks are altogether crystalline. On the other hand, the Silurian limestones are mere mudstones, and quite uncrystalline, so that there is no real law on the subject.

Whenever limestones are not distinctly metamorphic, they bear traces of organic structure. This is so much the case as to justify the assumption by geologists that all limestone is the result of organic action at some period or other. The indication of life is of various kinds, often microscopic. Corals, shells, and even bones make up in some cases the entire mass of large deposits. In other cases the limestone consists of minute particles of such bodies so cemented and combined into a solid, that it is scarcely possible without minute investigation to discover the secret. Shelly limestones of the oolitic period, such as are common at Bath and Portland Island, afford good examples of the first, and chalk of the latter condition.

Lime Burning. Although all carbonates of lime may, by burning, be brought to the state of quicklime, chalk and compact limestone are alone used for this purpose in the large way. The limekiln at present almost universally employed in this country is a cup-shaped concavity, in a solid mass of masonry, open at top and terminated at bottom by a grate, immediately above which is an iron door. This simple furnace is first charged with fuel (either wood, or coal and cinders), upon which is afterwards laid a stratum about a foot thick of chalk or limestone, broken into pieces not larger than the fist; to this succeeds a charge of fuel, and so on alternately, keeping the kiln always full, The pieces of limestone descend towards the bottom of the kiln in proportion as the fuel is consumed, being in the meantime kept at a pretty full red heat. At this temperature, the water and carbonic anhydride are driven off; and by the time the limestone arrives at the bottom of the kiln, which happens in about fortyLimestones are extremely useful, and thereeight hours, it is rendered perfectly caustic. The fore it is very important to discover them in door above the grate is then opened, and the every country. Of themselves, when in suffilime below the next descending stratum of fuel cient abundance, they generally make excellent is raked out; the remaining contents of the building material. When not so used, they furnace sink down, and a fresh charge is laid may be burnt to produce lime, either to work on the top. The compact limestone, after hav-up into mortar, or employed for agricultural ing undergone this process, though lighter and purposes. Forming part of a soil, the disintemore porous than before, still retains its figure grated fragments that are loosened from the unaltered; hence it is readily separable from rock below often mix with clay and produce the ashes of the fuel, and is sufficiently hard to useful soils during their slow decomposition. be carried from place to place without falling Worked up into the soil in a powdery state, to pieces. The management of the kiln as to they form marls and other useful admixtures. temperature varies with the nature of the lime- In England the limestones are of four kinds : stone, which if silicious and overheated is apt compact limestones, passing into marble of the to be partially vitrified; such lime slakes im- carboniferous and Devonian period, oolitic perfectly, leaving a core, and is said to be limestones; mudstones, or impure clayey limedead-burnt. stones, and marlstones, from both of which Attempts have been made to burn lime, or, hydraulic cement is made; and chalk. The in other words, to expel the carbonic anhydride Silurian limestones are, for the most part, mudfrom limestone, in close vessels, but the carbonic stones; the lias yields marlstone; and the rest anhydride cannot be so driven off. belong to the middle and upper part of the