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sentry, and serving to convey the chyle to its destined place. See CHYLE.

LACTESCENT, in botany, a term applied to the juices of plants, of whatever colour, which flow out of plants when any injury is done them. The colour is either white, as in the campanula, maple, dandelion, &c.; or yellow, as in the celandine, &c.; or red, as in the bloody dock. Most latescent plants are poisonous, excepting those with compound flowers, which are generally of an innocent quality.

LACTIC ucid, in chemistry, is contained in milk, and was discovered by Scheele, to whom modern chemistry is indebted for much important knowledge. The formation of this acid depends on the change of the saccharine mucous matter; for after the acid is once well formed, when the serous part of the milk reddens vegetable blues, no more is obtained by evaporation and crystallization. Scheele obtained this acid by the following process: he evaporated sour whey to one-eighth of its bulk, and then filtered it to separate the coagulated cheesy matter. He then added lime water to precipitate the phosphate of lime, and diluted the liquid with pure water. He next precipitated the excess of lime by means of the oxalic acid, and then evaporated the solution to the consistence of honey, poured on a quantity of alcohol which separates the portion of sugar, of milk, and other extraneous matter, and dissolves the lactic acid, and distilled the clear filtered liquor till the whole of the alcohol employed be driven off: what remains is the lactic acid. This acid is never crystallised, but always appears in the form of a viscid mucilaginous substance; it has a sharp taste; it reddens tincture of turnsole; and gives a reddish shade to the syrup of violets. It combines with alkalies, earths, and metallic oxides; and forms with them lactates.

LACTUCA, in botany, lettuce, a genus of the Syngenesia Polygamia Equalis class and order. Natural order of Compositæ Semiflosculosæ. Cichoraceæ, Jussieu. Es sential character: calyx imbricate, cylindrical, with a membranaceous margin; receptacle naked; seeds even, with a simple stipitate down. There are eleven species, of which L. sativa, the common garden lettuce, with its several varieties are too well known to need a particular description.

LACUNAR, in architecture, an arched roof or ceiling, more especially the planking or flooring above porticos and piazzas. LADDERS, scaling, in the military art,

are used in scaling when a place is to be taken by surprise. They are made several ways; sometimes of flat staves, so as to move about their pins and shut like a parallel ruler, for conveniently carrying them: the French make them of several pieces so as to be joined together, and to be capable of any necessary length: sometimes they are made of single ropes knotted at proper distances, with iron hooks at each end, one to fasten them upon the wall above, aud the other in the ground; and sometimes they are made with two ropes, and staves between them to keep the ropes at a proper distance, and to tread upon. When they are used in the action of scaling walls they ought to be rather too long than too short, and to be given in charge only to the stoutest of the detachment.

The soldiers should carry these ladders with the left arm passed through the second step, taking care to hold them upright close to their sides, and very short below, to prevent any accident in leaping into the ditch. The first rank of each division, provided with ladders, should set out with the rest at the signal, marching resolutely with their firelocks slung, to jump into the ditch; when they are arrived they should apply their ladders against the parapet, observing to place them towards the salient angle rather than the middle of the curtain, because the enemy has less force there. Care must be taken to place the ladders withir a foot of each other, and not to give them too much nor too little slope, so that they may not be over-turned, or broken with the weight of the soldiers mounting upon them. The ladders being applied, they who have carried them, and they who come after should mount up and rush upon the enemy sword in hand; if he who goes first happens to be overturned, the next should take care not to be thrown down by his comrade; but on the contrary, immediately mount himself so as not to give the enemy time to load his piece. The success of an attack by scaling is infallible, if they mount the four sides at once, and take care to shower a number of grenades among the enemy, especially when supported by some grenadiers and piquets, who divide the attention and share the fire of the enemy.

LADEN; the state of a ship when she is charged with a weight or quantity of materials equal to her tonnage or burthen. If the goods with which she is laden be extremely heavy, her burthen is determined by the weight thereof; but if light, she

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carries as much as she can stow for the purposes of navigation. As a ton in measure is generally estimated at 2000 pounds in weight, a vessel of 200 tons ought accordingly to carry a weight equal to 400,000 pounds; therefore, when the matter of which the cargo is composed is specifically heavier than the water in which she floats; or, in other words, when the cargo is so heavy that she cannot float high enough with so great a quantity of it as her hold will contain, a diminution thereof becomes absolutely necessary.

LAETIA, in botany, so named from John de Lact of Antwerp, a genus of the Polyandria Monogynia class and order. Natural order of Tiliaceæ, Jussieu. Essential character: calyx five-leaved; corolla five-petalled, or none; fruit one-celled, three-cornered; seeds with a pulpy aril. There are four species, of which L. guidonia is a tree which grows to a considerable size in Jamaica, and is esteemed highly for its fine timber, which is much used in all sorts of building; in the fruit of this tree, the lines between the valves are of a beautiful red colour, as well as the placenta; the filaments of the flower are very nume

rous.

LAGERSTROEMIA, in botany, so named from Magnus Lagerstroem, of Gottenburgh; a genus of the Icosandria Monogynia class and order. Natural order of Salicariæ, Jussieu. Essential character: calyx six-cleft, bell-shaped; petals six, curled; stamina very many, the six outer thicker than the rest, and longer than the petals. There are four species, of which L. indica, according to Linnæus, is a tree the size of a pomegranate, with opposite leaves, sub-sessile, oblong, quite entire, smooth; the floral leaves roundish; flowers flesh-coloured, in a loose terminating thyrse, on trifid or three-flowered pedicels; the petals, on long claws, six in number, curled and waved. Native of the East Indies, China, Cochin China, and Japan.

LAGOECIA, in botany, a genus of the Pentandria Monogynia class and order. Natural order of Umbellatæ, or Umbelliferæ. Essential character: involucre universal, and partial: petals bifid; seeds solitary, inferior. There is but one species, viz. L. cuminoides, wild or bastard cumin: this is an annual plant, about a foot high; the leaves resemble those of honeywort: the flowers are collected into spherical heads, at the extremity of the stalks, and are of a greenish yellow colour. Native of the Levant.

LAGUNA, in botany, so called from Andreas Laguna, a Spanish physician and botanist; a genus of the Monadelphia Polyandria class and order. Natural order of Columniferæ. Malvaceæ, Jussieu. Essential character: calyx simple, five-cusped; style simple; stigma peltated; capsule fivecelled, five-valved. There are three species, of which L. aculeata, prickly lagunœa, has a round tomentose stem, armed with small upright prickles, a little branched, and is about a foot and a half in height; leaves alternate, shorter than the petioles, deeply divided into three serrate-toothed segments, the middle one longer than the others; flowers on short peduncles; calyx tomentose, terminating in five short awlshaped points, bursting on one side to the middle, when the corolla expands, which is yellow, and twice as long as the calyx; filaments short, scattered over the whole surface of the tube; stigma red, peltate, scarcely standing out; capsule oblong, acuminate, five-cornered, tomentose; seeds kidney-form, black. It is a native of Coromandel, near Pondicherry, where it is callby the inhabitants, Cattacacheree.

LAGURUS, in botany, a genus of the Triandria Digynia class and order. Natural order of Gramina, Gramineæ, or Grasses. Essential character: calyx two-valved, with a villose awn; corolla having, on the outer petal, two terminating awns, and a third dorsal one, twisted back. There is but one species, viz. L. ovatus, an annual grass, eighteen inches or more in height; very soft and hoary, as are also the leaves and spikes. Native of the South of Europe.

LAKE, in the arts, is a combination of colouring extract, with an earth, or metallic oxide, formed by precipitation from the solution of the colouring matter. If a solution of alum is added to an infusion of madder, a mutual decomposition takes place, and part of the alumine falls united with the colouring matter of the madder. Precipitates, of different shades of colour, are obtained with alum, nitre, chalk, acetate of lead, and muriate of tin. The lakes form some of the beautiful pigments, and are highly esteemed in water-colour painting, and other purposes: and they are almost invariably composed, either of alum, or sometimes the solutions of tin, and some other watery solution of a colouring matter. See COLOUR.

LAMA, the sovereign pontiff, or rather god of the Asiatic Tartars, inhabiting the country of Barantola. The Lama is not only adored by the inhabitants of the coun

try, but also by the kings of Tartary, who send him rich presents, and go in pilgrim age to pay him adoration, calling him Lama congiu, i. e. god, the everlasting father of heaven. He is never to be seen but in a secret place of his palace, amidst a great number of lamps, sitting cross-legged upon a cushion, and adorned all over with gold and precious stones; where, at a distance, they prostrate themselves before him, it not being lawful for any to kiss even his feet. He is called the Great Lama, or Lama of Lamas, that is, priest of priests: and, to persuade the people that he is immortal, the inferior priests, when he dies, substitute another in his stead, and so continue the cheat from generation to generation. These priests persuade the people, that the Lama was raised from death many hundred years ago, that he has lived ever since, and will continue to live for ever.

LAMB. See OVIS.

LAMINÆ, the thin plates of which any thing consists; hence the epithet laminated, which is applied to those bodies whose texture discovers such a disposition as that of plates lying over one another.

LAMIUM, in botany, archangel, a genus of the Didynamia Gymnospermia class and order. Natural order of Verticillatæ. La biatæ, Jussieu. Essential character: corolla upper lip entire, vaulted; lower, twolobed; throat with a reflex toothlet on each side. There are thirteen species, several of which are considered as weeds, rather than garden plants. The L. album, white archangel, or dead nettle, is common in hedges, on banks, and by road-sides; flowering in April and May, when it is much resorted to by bees, for the honey secreted in the bottom of the tube, by the gland that surrounds the base of the germ. This plant has a disagreeable smell when bruised. Phalana Chrysitis, or burnished-brass moth feeds on it: Linnæus says, the leaves are eaten in Sweden as a pot-herb, in the spring; no cattle, however, seem to touch it; and, having à strong, creeping, perennial root, it should be extirpated, which is not difficult.

LAMP, Argand's. This is a very ingenious contrivance, and the greatest improvement in lamps that has yet been made, It is the invention of a citizen of Geneva; and the principle on which the superiority of the lamp depends is the admission of a larger quantity of air to the flame than can be done in the common way. This is accomplished by making the wick of a circular

form, by which means a current of air rushes through the cylinder on which it is placed with great force; and, along with that which has access to the outside, excites the flame to such a degree, that the smoke is entirely consumed. Thus both the light and heat are prodigiously increased, at the same time that there is very considerable saving in the expense of oil, the combustion being exceedingly augmented by the quantity of air admitted to the flame; and that what in common lamps is dissipated in smoke is here converted into a brilliant flame. This lamp is now very much in use; and is applied not only to the ordinary purposes of illumination, but also to that of a lamp furnace for chemical operations, in which it is found to exceed every other contrivance yet invented. It consists of two parts; viz. a reservoir for the oil, and the lamp itself. The reservoir is usually in the form of a vase, and has the lamp proceeding from its side. The latter consists of an upright metallic tube, about one inch and sixtenths in diameter, three inches in length, and open at both ends. Within this is ano ther tube, about an inch in diameter, and nearly of an equal length; the space betwixt the two being left clear for the passage of the air. The internal tube is closed at the bottom, and contains another similar tube, about half an inch in diameter, which is soldered to the bottom of the second. It is perforated throughout, so as to admit a current of air to pass through it; and the oil is contained in the space betwixt the tube and that which surrounds it. A particular kind of cotton cloth is used for the wick, the longitudinal threads of which are much thicker than the others, and which nearly fills the space into which the oil flows; and the mechanism of the lamp is such, that the wick may be raised or depressed at pleasure. When the lamp is lighted, the flame is in the form of a hollow cylinder; and by reason of the strong influx of air through the heated metallic tube becomes extremely bright, the smoke being entirely consumed for the reasons already mentioned. The heat and light are still farther increased, by putting over the whole a glass cylinder, nearly of the size of the exterior tube. By diminishing the central aperture the heat and light are proportionably diminished, and the lamp begins to smoke. The access of air both to the external and internal surfaces of the flame is indeed so very necessary, that a sensible difference is perceived when the hand is

held even at the distance of an inch below the lower aperture of the cylinder; and there is also a certain length of wick at which the effect of the lamp is strongest. If the wick be very short, the flame, though white and brilliant, emits a disagreeable and pale kind of light ; and if very long, the upper part becomes brown, and smoke is emitted. The saving of expense in the use of this instrument for common purposes is very considerable. By some experiments it appears, that the lamp will continue to burn three hours for the value of one penny; and the following was the result of the comparison between the light emitted by it and that of a candle. The latter having been suffered to burn so long without snuf fing, that arge lumps of coaly matter were formed upon the wick, gave a light at 24 inches distance equal to the lamp at 129 inches: whence it appeared, that the light of the lamp was equal to 28 candles in this state. On snuffing the candle, however, its light was so much augmented, that it became necessary to remove it to the distance of 67 inches, before its light became equal to that of the lamp at 129 inches: whence it was concluded, that the light of the lamp was somewhat less than that of four candles fresh snuffed. At another trial, in which the lamp was placed at the distance of 131 inches, and a candle at the distance of 55 inches, the lights were equal. In these experiments the candles made use of were 10 inches long, and 2 inches in diameter. When the candle was newly snuffed it appeared to have the advantage; but the lamp soon got the superiority; and on the whole it was concluded, that the lamp is at least equivalent to half a dozen of tallow candles, of six in the pound; the expense of the one being only 2d. and the other 8d. in seven hours.

We shall now give a more particular description of Argand's lamp, with reference to figures. Fig. 1, Plate Argand's Lamp, is an upright elevation; tig. 2, a section; and tigs. 3, 4, and 5, parts of this useful instrument. AA (fig. 1 and 2) is a reservoir containing oil, whose shape is immaterial; in the present instance it is that of an urn: B is a tube to convey the oil to the lamp, where it is consumed. The lamp is composed of several tubes, one within the other: the external, a a, is only a case to defend the others within it, having a small cup, bb, screwed to it at bottom, to receive the dropping of oil: at d the tube is enlarged by a projection soldered to it,

and into which the tube B delivers the oil it brings from the urn A A: ee (fig. 2) is the second tube, supported concentrical with the other by the enlargement d, which it is open to all down one side; the oil, therefore, has free passage into this tube; but as it is closed at bottom, and the cavity, d, tight, it cannot get in the external tube, a a: ff is the internal tube, supported by being soldered to the bottom of the second, e e: another moveable tube is placed between the tube e e and ƒƒ, as seen in the section (fig. 2), but better explained in a separate figure (fig. 4), where gh is the tube; it is divided by a slit from top to bottom on the side g; on each side of this slit a small piece of brass plate, i, is soldered to support a frame, k, in which a small pinion works (as shewn in fig. 2); this pinion gives motion to a rack, l, (fig. 5) bent at right angles at the lower end, and holding a short tube, or rather ring, m, on which the wick, a, is held; this ring and the wick slides within the tubes g h, and outside of the internal tube, ƒƒ, its arm connecting it with the rack, 1, goes first through the slit down the side, g, of the tube (fig. 4), and next through the opening in the side of the tube, e e,where it communicates with the cavity d. At the top of the lamp a glass chimney,

o, is fixed, (as shewn in fig. 3), where o o is the glass tube, with a small enlargement or ring at the bottom: pp is a brass ring going over the glass, and catching the rim at the bottom ; it is cut into a female screw withinside, and screwed upon another ring, r; this presses against the bottom edge of the glass tube, and thus holds it fast between them: the ring r fits tight by friction upon the top of the tube a a; but so as to be easily removed when the glass is to be cleaned or taken away. The great advantage of this lamp is, that the wick is hollow, and the air brought to it, both on the inside by the tubes ƒƒ, and outside between the tubes e and a a, and by the rarefaction of the air in the glass chimney, a considerable draught is created, and the air forming, which is forced to pass through the flame. In the urn, A, is a contrivance to regulate the quantity of oil coming from it, that the lamp may not be overflowed: it unscrews at t, (fig. 2) and terminates below the screw in a small pipe, v, closed at bottom; a hole is made in the side of this pipe, through which the oil flows: it is closed occasionally by a small tube sliding upon the other, v, and moved by a small handle, t, coming through the screw, t: a small hole should be drilled through the

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screw in the same direction as the wire of the handle, t, to supply air to this part. When the urn is to be filled with oil, it is unscrewed at t, and the oil poured in at the hole in tube v: the hole must then be closed, by pushing down the handle, t: the oil cannot now get out, and the urn is screwed into its place; when the handle, t, is pushed down the hole is opened, by removing the tube, u, from before the hole in the pipe, v: the oil now runs out, the air entering at the same hole, until it rises in the cistern at the end of the pipe, B, above the level of the hole; the air cannot now enter, and consequently the oil will not come out, until by the burning of the lamp the oil is drawn down below the hole, a bubble of air then gets into the urn, and an equivalent drop of oil runs down by this means, though the lamp is always plentifully supplied, yet it never runs over.

LAMP black. See COLOUR. LAMPYRIS, in natural history, fire fly, a genus of insects of the order Coleoptera. Antennæ filiform; four feelers; shells flexile; thorax flat, semi-orbicular, surround- ́ ing and concealing the head; segments of the abdomen terminating in folded papille: female usually apterous. There are nearly sixty species, in four divisions, viz. A. feelers subclavate: B. fore-feelers hatchetshaped: C. feelers sub-filiform: D. first joint of the feelers thicker and truncate. The first of these divisions is subdivided into those which have entire horny lips; and into those with an emarginate membrana ceons lip. The body of the insect in this genus is oblong, with the sides formed into a kind of soft papillæ, lapping over each other. L. noctiluca, or common glowworm, is seen during the summer months, on dry banks, about woods, pastures, and hedgeways, exhibiting, as soon as it is dusk, vivid and phosphoric splendour, in form of a round spot of considerable size. The animal itself, which is the female insect, measures about three quarters of an inch in length, and is of a dull, earthy-brown/colour on the upper parts, and beneath more or less tinged with rose colour, with the two or three last joints of the body of a pale or whitish sulphur colour. It is from these parts that the phosphoric light proceeds. The body, exclusive of the thorax, consists of ten joints. The larva and pupa do not greatly differ from the complete insect, but the phosphoric light is strongest in the complete animal. The male is smaller than the female, and is provided

with wings and wing-sheaths: it is very uncommon; and it is not determined whether it be luminous or not. Naturalists have commonly supposed, that the splendour of the female is designed for the purpose of attracting the male. In Italy, the flying glow-worm is extremely common; and it is said that, on grand occasions, ladies use them as ornaments for their head-dress in evening parties.

LANA, in botany, wool, a species of pubescence, down, or velvet, which serves to screen the leaves, covered with it, from the heat: this appearance is very conspicuous in the horehound, woolly thistle, &c.

LANA philosophica, flowers of zinc. See ZINC.

LANARIA, in botany, a genus of the Hexandria Monogynia class and order. Natural order of Ensatæ. Irides, Jussieu. Essential character: corolla superior, woolly, longer than the filaments; border six-parted, somewhat spreading; capsule threecelled. There is but one species, viz. L. plumosa, woolly lanaria, a native of the Cape of Good Hope.

LANCET, a chirurgical instrument, sharp-pointed, and two-edged, chiefly used for opening veins in the operation of phlebotomy, or bleeding; also for laying open abscesses, tumours, &c.

LANGUAGE. 1. Man, it has frequently been said, is the only animal possessed of speech, and if we use this term as implying the expression of a train of ideas by articulate sounds, it may perhaps be esteemed the best criterion of distinction between man and the inferior animals. It is not easy to fix upon one which shall be universally applicable; but the same difficulty frequently occurs in the attempt to ascertain the exact boundary between the characteristics of one class of being and those of another: for instance, the naturalist finds it a puzzling problem to ascertain the characteristic difference between the animal and the vegetable kingdom. Some of the most intelligent of the brute creation often astonish us by actions which can proceed only from powers of intellect similar to those which we possess. All the mental powers, except sensation, are probably the modifications of the principle of association: it is acknowledged that brutes possess this in a considerable degree, and it is probable that to the difference in the extent of this principle of its activity and direction, we are to attribute the mental difference between one animal and another. There is, perhaps, less difference

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