Augustus, though some maintain that he only added the portico; but of this there is no proof, as no mention is made of this celebrated building before his time. We find from Vitruvius (lib. iii. c. 3,) that the floors of temples were frequently supported by vaults, and (lib. v. c. 1.) that the roofs of basilicas were vaulted of the tortoise form, which he distinguishes by the name of testudo. This form of vaulting is very flat, with four curved sides springing from each of the four walls, and it approaches nearly to that of a flat dome upon a rectangular plan.

We also find, from the remains of Roman buildings, the ceiling of their apartments vaulted. The side apartments, or chapels, of the Temple of Peace, and of the baths of Dioclesian, have vaults with cylindrical intradoes, while the great rectangular apart ment in each of these edifices is vaulted in the groined form; and it is remarkable that the groins are not formed by the intradoes of the vaults in the chapels, for the summits of the vaults in these rises but a small distance above the springing of the middle groins. It may also be remarked, that the piers between the chapels have small arcades, the summits of which are consider ably below the cylindrical intradoes of the side vaults. This circumstance is not peculiar to these buildings, as is to be found in many others. in the plates of the temple of Peace, by Desgodetz. The Romans employed annular vaults, as in the temple of Bacchus ; and in this, as in the temple of Peace, and the baths of Dioclesian, the summits of the arcades supporting the cylindric wall and dome of the central apartment do not intersect the annular intrados; but the convex side of the cylindric wall which supports this annular intrados, and consequently do not form groins. The intradoes of the Roman domes are of a semicircular section, as may be seen in the Pantheon, the temple of Bacchus at Rome, the temple of Jupiter, and vestibule of the palace of Diolesian, at Spalatro, in Dalmatia, while the vertical section of the extradoes through the axis is a much less segment, as the Pantheon at Rome, and the vestibule and palace of Dioclesian exhibit. We have no instances among the Roman or Grecian buildings of pendentives or spandrels which are supported by four pillars, or by quadrangular or polygonal walls, and which support themselves on a spheric dome or cylindrical wall. Pendentives rising from four pillars, and a dome from the

This is to be seen distinctly

top of the pendentives, were first put in practice, it is said, in the celebrated church of Sancta Sophia at Constantinople.

In the rectangular buildings of the middle ages quadrangular, equal-pitched groins were generally used; and in circular buildings we have annular groins, as in the Church of the Holy Sepulchre at Cambridge, and Temple Church, London. We have also mentioned those curious groins which are exhibited in the ceilings of King's College Chapel, Cambridge; St. George's Chapel, Windsor; and King Henry the Seventh's Chapel, Westminster, of modern invention.

In the present day every species of vaulting, that were either used by the ancients or throughout the middle ages, are employed, both for the sake of variety and for elegance.

It does not appear that the ancients were acquainted with cylindrical, unequal-pitched groins, at least by way of ornament; this form is however very beautiful, as the arcades above the passage through the front of Somerset-House clearly exhibit.

ARCHYTAS, of Tarentum, in biography, a celebrated mathematician, cosmographer, and Pythagorean philosopher, of whom Horace says

Maris ac terræ, numeroque carentis arena

Mensorem cohibent, Archyta, &c. He flourished about 400 years before Christ, and was the master of Plato, Eudoxus, and Philolaus. He gave a method of finding two mean proportionals between two given lines, and thence the duplication of the cube, by means of the conic sections. His skill in mechanics was such, that he was said to be the inventor of the crane and the screw; and he made a wooden pigeon that could fly about, when it was once set off; but it could not rise again of itself, after it rested. He wrote several works, though none of them are now extant, particularly a treatise IT Пavlos, De Universo, cited by Simplicius in Arist. Categ. It is said he invented the ten categories. He acquired great reputation both in his legislative and military capacity; having commanded an army seven times without ever being defeated. He was at last shipwrecked, and drowned in the Adriatic sea.

Archytas was distinguished through life by modesty and self-command. He maintained that virtue was to be pursued for its own sake, in every condition of life; that

all excess is inconsistent with virtue; that the mind is more injured by prosperity than by adversity; that there is no pestilence so pernicious to human happiness as pleasure; and that the love of it is a disease destructive to the human mind.

ARCTIC, in astronomy, an epithet given to the north pole, and likewise to a circle of the sphere parallel to the equator, and 23 degrees 30 minutes distant from the north pole.

ARCTIUM, the burdock, in botany, a genus of the Syngenesia Polygamia Equalis class of plants; the common calyx of which is globose and imbricated; the compound flower is tubulated and uniform, with equal hermaphrodite corollulæ : the proper flower is monopetalous and tubulous, with a slender and very long tube; there is no pericarpium; the cup is connivent, and the seed single, vertically pyramidical, and crowned with a simple down shorter than the seed. There are two species; viz. the Laffa and Bai dana.

ARCTOMYS, the marmot, in natural history, a genus of the Mammalia class of animals, of which the generic character is, front teeth two in each jaw, strong, sharp, and cuneated; grinders in the upper jaw, five on each side, in the lower jaw four; clavicles or collar bones perfect. This geaus differs but little from the Mus tribe, so that naturalists have sometimes doubted whether they should be separated into distinct genera. They are diurnal animals; feed on roots, grain, and fruits, which they often collect in heaps. They reside in subterraneous holes, and become torpid in the winter. The head is gibbous, or rounded, with short ears, or none; body thick; tail short; hairy; fore feet four-toed, with a very short thumb; hind feet five-toed; cœcum large. There are eleven species, of which we shall notice the following: 1. Arctomys marmota, or Alpine marmot: ears short, round; body brown, beneath reddish. It inhabits dry open places, on the summits of the Alps and Pyrenees; feeds naturally on roots, herbs, and insects; when tamed it will eat any thing that is offered; drinks little; basks in the sun; lives among small tribes, with a centinel placed to give notice of danger, which is done with a hiss ; forms a burrow with many chambers and entrances, for the summer; another lined with soft grass, in which it remains torpid during winter; it eats with its fore paws; walks on its heels, often erect; is easily caught when out of his burrow; in a tame state very destruc

tive of food, cloaths, and furniture; hardly kept awake in winter, even in warm chambers; gravid seven weeks, and brings from two to four at a time. These animals make no provision for the winter, but as soon as the frosts set in, they carefully stop up the entrances to their mansions, and gradually fall into a state of torpidity, in which they continue till the beginning of spring, when they awake and commence their excursions. Before they retire to winter quarters they grow excessively fat, and appear very emaciated on first emerging from them. If carefully dug up during the winter, they may be conveyed away in their sleeping state, and when brought into a warm chamber gradually awaken.

The Quebec marmot is rather larger than a rabbit, with short ears and a round head. It inhabits Hudson's Bay and Canada. A. monax, or Maryland marmot is found in various parts of North America, and in its habits and manners is very like that already noticed. The marmot, when taken young, may be easily domesticated, and taught to perform various gesticulations, such as holding a stick, dancing, &c. See Plate II. Mammalia, in which will be seen the hamster and lemming, sometimes called the Lapland marmot: descriptions of these will be found in the article Mus. A. bobac, or grey marmot is a native of the high, but milder and sunny sides of mountainous countries, which abound with free-stone rocks, where it is found in dry situations. It frequents Poland and Russia, among the Carpathian hills: it swarms in the Ukraine, about the Boristhenes, and between this river and the Don, and along the range of hills which extend to the Wolga. It is found about the Yaik, and inhabits the southern desert in Great Tartary. It is not to be seen in Siberia, on account of its northern situation, and rarely reaches in Kamschatka as high as 55°. The colour is grey above, with the throat, inside of the limbs, and under parts of the body fulvous or ferruginous; the tail is short, rather slender, and full of hair. Its manner of life resembles the Alpine marmot. The holes of these animals are lined with the finest hay, and in such quantities that, it is said, enough has been found in a single receptacle to feed a horse for a night. A. citillus, or variegated marmot, is the most beautiful of all the species; in size it differs very much; some are as large as the Alpine marmot, and others not larger than a common water rat. The variegated marmot inhabits Bohemia and

other parts of Germany, from the banks of the Wolga to India aud Persia, through Siberia and Great Tartary to Kamschatka, and even the continent of America. It is not certain that these sleep in the winter like others of the Arctomys genus. They breed in the spring, and produce from five to eight at a time. They are said to be irrascible and quarrelsome among themselves, and their bite is very severe. They feed not only on animal food, but on small birds and other animals, which they will kill. They are easily tamed, and will grow familiar in a few days. They are extremely clean, and after feeding, generally wash their faces, and clean their fur. Like other domestic animals, they are fond of being caressed, and will feed from the hand. Their sleep is profound during the whole night, and in cold and rainy weather through the greater part of the day. See Plate II. Mammalia, fig. 1, 2, and 5.

ARCTOPUS, in botany, a genus of the Polygamia Dioecia class of plants, the general umbel of which is long nnd unequal; the partial umbel is shorter; the involucra consist of five leaves; the corolla of five petals; the fruit is single and bilocular, and stands under the receptacle of the floscule; the seed is single, cordated, and acuminated. There is but one species.

ARCTOTHECA, in botany, a genus of the Syngenesia Necessaria: receptacle cellular and chaffy; calyx imbricate. There is but one species.

ARCTOTIS, in botany, a genus of the Syngenesia Necessaria class of plants, the common calyx of which is roundish and imbricated; the compound flower is radiated; the hermaphrodite corollulæ are tubulous and numerous in the disk: the proper hermaphrodite flowers are funnel-shaped; there is no pericarpium; the seed is single, roundish, and hairy. This genus is separated into the following divisions: A. receptacle villous, 31 species; B. receptacle chaffy, 11 species; C. doubtful, 18 species. ARCTURUS, a fixed star of the first magnitude, in the skirt of Boötes: so called from the circumstance of its being near the tail of the Bear. It has been thought to be the nearest fixed star to our system visible in the northern hemisphere, because the variation of its place, in consequence of a proper motion of its own, is more remarkable than that of any other of the stars, and by comparing a variety of observations respecting the quantity and direction of the motion of this star, he infers,

that the obliquity of the ecliptic decreases at the rate of 58" in 100 years, a quantity that nearly corresponds to the mean of the computations framed by the celebrated Euler and Lalande, upon the more unerring principles of attraction.

ARCTUS, in astronomy, the Greek name for the Ursa Major and Minor.

ARDEA, in natural history, a genus of birds of the order Gralla. The characters of this genus are, a long, strong, sharp-pointed bill; nostrils linear; tongue pointed; toes connected by a membrane as far as the first joint; the middle claw of some of the species, of which there are 79, pectinated. This genus is separated into five divisions, viz. A. crested; bill hardly longer than the head; B. cranes, bald; C. storks, orbits naked; D. herons, middle claw serrate inwardly; E. bill gaping in the middle.

Some ornithologists have separated the herons from the storks and cranes; others preferring the Linnæan system, class the whole under one genus, which according to Gmelin, consistis of nearly 100 species, though Latham enumerated but 79. They are widely distributed over various parts of the globe, differing in size, figure, and plumage, and with talents adapted to their various places of residence, or their peculiar pursuits. But notwithstanding the variety in their bills and plumage, the manners of all are nearly the same, so also is their character which is stigmatized with cowardice and rapacity, indolence and yet insatiable hunger; and it has been observed that from the meagre-looking form of their bodies one would suppose the greatest abundance almost insufficient for their support.

Ardea pavonia. This is as large as the common heron; the length two feet nine inches; the bill is two inches and a half long, straight, and of a brownish colour; irides grey; the crown of the head covered with soft black feathers like velvet; on the hind part is a tuft composed of hair, or rather bristles, arising near each other at the base, and spreading out on all sides in a globular form; this is four inches in length, and of a reddish brown colour; the sides of the head are bare of feathers, being covered only by a fleshy membrane, of a reddish colour at the lower part, and in shape not unlike a kidney; on each side of the throat hangs a kind of wattle; the general colour of the bird bluish-ash; the feathers on the fore part of the neck are very long, and hang over the breast; wing coverts white; the greater ones incline to rufous, and those

resenting it as done to themselves. At Bagdad they are to be seen on every house, wall, and tree, quite tame. At Persepolis the remains of the pillars serve them to build on, every pillar having a nest. They are thought to have two broods in a year, the first towards the north, the latter in warmer places; and are seen in vast flocks during their migrations. The female makes a large nest and lays from two to four eggs. The young are hatched in a month; the male and female watch them by turns till they can provide for themselves. The stork sleeps on one leg, and snaps with its bill in a singular manner. Its food consists in snakes and other reptiles; hence the veneration of all persons for this bird which frees them from such pests.

, Ardea stellaris, or bittern. This is an elegant species, and is somewhat less than the heron; length two feet six inches; the bill brown, beneath inclining to green; irides yellow; the head feathers are long, and those of the neck loose and waving; the crown of the head black; the lower jaw on each side dusky; the plumage in general is beautifully variegated; the ground a ferruginous yellow, palest beneath, marked with numerous bars, streaks, and zigzag lines of black; the legs are pale green; claws long and slender; and the inner edge on the middle claw serrated. The female is less, darker coloured, and the feathers on the head and neck less flowing than in the male. This is a common bird in our islands, and we believe in most of the temperate parts of the continent; in some of the colder, migratory; with us it remains the whole year; frequents marshy places, and especially where reeds grow, among which it makes the nest, in April, which is chiefly composed of a bed of rushes, &c. The female lays four or five eggs of a pale greenish ash colour; the young are hatched in twenty-five days. It is an indolent bird, stirring very little in the day unless disturbed; though if once roused is not difficult to shoot, as it flies heavily. In the evening, after sun-set, it is seen to soar aloft in a spiral ascent, till quite out of sight, and this chiefly in autumn, making a singular kind of noise; it has also another noise, like that of a bellowing bull, beginning in February and ceasing after breeding-time; but this is done while on the ground. If attacked by dogs or men, it defends itself well; and is said to strike at the eyes of the enemy. The food is frogs, mice, and other reptiles, which it swallows whole, as well as fish. Latham remembers to have found

two middle-sized trouts in the stomach of one perfectly whole. It is reckoned pretty good eating. See Plate III. Aves, fig. 7. and Plate IV. fig. 1.

ARDISIA, in botany, a genus of the Pentandria Menogynia class and order. Calyx five-leaved; corol salver-shaped, with the border reflected; antheræ large, erect; stigma simple; drupe superior; one-seeded. There are nine species.

ARDUINA, in botany, a genus of the Pentandria Monogynia class and order. Corol one-petalled; stigma bifid; berry twocelled; seeds solitary; a shrub of the Cape of Good Hope.

ARE, in French measure, is a superficial unit, or a square, the side of which is 100 metres in length, or 10,000 square metres; the rectilineal metre being 3.281 feet, the are will be 1076.49 square feet. The tenth of an are, called deciare, is a superficies 100 metres long, and 10 broad; or 1000 square metres 1076.49; and the centiare equal to 100 square metres, is 1076.49 square feet. See MEASURE.

AREA, in geometry, denotes the superficial content of any figure; thus, if we sup. pose a parallelogram six inches long, and four broad, its area will be 6 x 4 = 24 square inches.

ARECA, in botany, a genus of plants, the characters of which are not perfectly ascertained; the calyx of the male flower is a bivalve spatha, the spadix is ramose; the corolla consists of three acuminated petals; the stamina are nine filaments, of which the three exterior ones are the longest; the female flowers are in the same spadix and spatha; the corolla is like the male corolla ; the fruit is a sub-oval fibrose drupe, surrounded at the base with an imbricated ca. lyx, and containing an oval seed.

There are three species, of which the oryz æformis is the cabbage-tree of the East Indies. The oleracea is found in the West Indies, the green tops of which are cut and eaten as a cabbage.

ARENARIA, sand-wor!, in botany, a genus of the Decandria Trigynia. Calyx five-leaved, spreading; petals five, entire ; capsule superior, one-celled, many-seeded. There are 36 species.

ARENARIUS, the name of a book of Archimedes, in which is demonstrated, that not only the sands of the earth, but even a greater quantity of particles than could be obtained in the immense sphere of the fixed stars, might be expressed by numbers, in a way invented and described by himself.

AREOMETER, an instrument by which