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portion and form of the column, its capital and its base, but also the composition and proportion of the entablature supported by the column and the distance of the columns from each other. These details differed in the different orders, and also, within well-defined limits, in the same order. The classification of the orders was made after Grecian architecture had ceased to be practiced, and is that of Vitruvius, ab. 14 B.C. The Grecian orders were the Doric, Ionic, and Corinthian. The occasional employment, notably in the Erechtheum at Athens, of representations of human figures, instead of columns, to support an entablature, has led some writers to add a
Caryatic order. The Parthenon at Athens, the most famous of Grecian buildings, is an octastyle (having eight columns in front), peripteral (entirely surrounded by columns) Doric temple. In the Doric order the stylobate (base) is continuous. each shaft resting directly upon it, without the intervention of a separate base; the columns are fluted, tapering slightly from the base, not regularly but with a slight outward curve (entasis), and four to six diameters in height. The capital consists of a necking (echinus), a convex curve (ovolo), and a straight-sided abacus. The entablature is subdivided into architrave, frieze and cornice, each of these members being subdivided. The frieze is a succession of triglyphs (upright members, each bearing two grooves), and metopes (square panels),the latter occupied by the sculptured and tinted reliefs that constitute the chief decoration of a Doric temple. Above the entablature at each end is the pediment, also occupied by a group of statuary. The Ionic order is supposed to have been derived from Asia, and Assyrian and Persian examples support this supposition, as respects its most distinguishing feature, the voluted capital. The Ionic order is more slenderly proportioned than the Doric, the column being, in the best examples, more than nine diameters in height, of which the molded |. occupies # of a diameter, and the capital, including the necking, 4 to 4. The entablature is subdivided as in the Doric order, but the frieze is continuous, the decoration being the richly carved moldings of the capital, architrave, and upper member of the cornice. Grecian Ionic
monly a height of 14 diameters, and decorated with the leaves of the acanthus conventionally designed and arranged. The column itself is ten diameters in height. The only complete example of the order in Greece is the choragic monument of Lysicrates at Athens. The Roman temples were imitated from those of the Greeks, and the imitation was in the main a debasement, tending to substitute an expression of luxury and magnificence for the more intellectual qualities of simplicity, purity and harmony of the originals. There is no completely developed Roman example of a Doric temple, and none of an Ionic temple that does not lose by comparison with the Greek. With the Corinthian order the case was somewhat different. As used in Greece, the elegance aimed at in this order degenerated into feebleness,
especially in the design of the capital. The Roman architects
and the cross vault; but none
ures, and applied to the faces
Roman Doric Order.
During the decline of the Empire and after its fall, the Roman methods of construction were adopted in all the countries in which the Romans had left monuments, and in these the influence of Roman building continued to be traceable throughout the whole of the Romanesque and Gothic periods, till 1400. The Basilica, a building of purely Roman type, is memorable as having furnished the type of the Christian church. It was a combined market-place, or merchants' exchange, and tribunal. It was a hall, its length twice to thrice its width. with a roof supported by columns; on each side of the colonnade was a lower building. The tribunal or court-room had a recess, often apsidal in plan, at one end, sometimes at each end, as in Trajan's at Rome, sometimes at one side, as in that of Fano, designed and described by Vitruvius. The basilicas were commonly of wood; our knowledge of them is derived from descrip; tions, from fragments of ground-plans preserved in tabletsand from examinations, as that of Trajan and of Pompeii,
tion which they employed. Diocletian's palace at Spalatro, 305, is the earliest building in which the Roman arched construction was employed as the basis of the architecture, the arches resting directly upon the columns, the irrelevant entablature omitted, and the colonnade converted into an arcade. This building is therefore said to be the beginning of Romanesque architecture, that of the column and the round arch, which prevailed throughout w. Europe for the ensuing seven centuries. The modern architecture of e. Europe and of Asia is not less derived from Roman sources. The builders of Byzantium applied to the Roman dome, as exemplified in the
Pantheon, the same rationalizing process which the early Romanesque builders applied to the wall-arch. The St. Sophia, in Constantinople, 532–537, is as clearly the earliest example of Byzantine building as the palace of Diocletian of w. Romanesque. In this is found the origin of the domed architecture of Mahometan countries, of the o of Spain, Egypt, Persia and India, as well as of the Greek Church architecture, including that of Russia. On the Italian shore of the Adriatic the style derived from Rome through Constantinople was practiced together with that derived directly from Rome. St. Mark's at Venice, consecrated 1085, and San Vitale at Ravenna. 530, are distinctly Byzantine buildings, and the style penetrated as far as Perigneux (St. Front; 1047) and even to Aix-la-Chapelle (Charlemagne's chapel, 796-804). These domed churches are exceptional; the Roman basilica remained the church type throughout western Europe. The desire for a durable roof of masonry was the motive of the development of Romanesque architecture. The mechanical difficulty of bridging wide spaces with masonry is illustrated in some Romanesque churches by the fact that while the aisles were roofed with groined vaulting, the wider naves were covered with continuous wagonvaults, as with roofs and ceilings of timber. The difficulty and awkwardness of uniting semi-circular arches of different spans and heights led to the introduction. in France, ab. 1150, of the pointed arch, which had been employed by the Arabian builders in Egypt, three centuries earlier. The application of this device made comparatively easy a more complicated system of vaulting than had before been possible. Within less than a century after its first appearance the vault-and-buttress system of the cathedrals was fully developed, while a system of modeling, with reference to the expression of function, had been extended to all the details of buildings. Gothic architecture prevailed throughout Europe during the 13th and 14th centuries. During the 15th the revival of letters in Italy led to a diligent study of the forms of classical architecture, and the result was the so-called Renaissance, in which these forms were again introduced. The onlv new structural form then introduced was a cupola, much taller in proportion to its diameter than that employed by the Roman or Byzantine, builders. The first example of this was furnished by Brunelleschi in the dome of the cathedral of Florence, 1420–44; it was followed by Alberti, Bramante, and Michelangelo (in St. Peter's at Rome), in which the dome was the dominating feature of the building, both within and without. Architectural details were borrowed or compiled from classical Roman architecture. The style thus formed has continued to prevail throughout Europe. In France, some parts of Germany. Great Britain, and America, churches are often designed in Romanesque or Gothic forms; and in these countries, especially in England, Germany, and the U. S., systematic efforts have been made, within the past half century, to revive mediaeval architecture, and to apply its
rinciples to secular as well as to ecclesiastical structures.
n spite of these efforts, the Renaissance continues to be the architectural style most in vogue with all civilized nations.
heat, which raises the terminals to vivid incandescence. If the carbons be horizontal, the upward current of air causes the luminous stream to assume an arched form; whence the name “electric arc.” The electric arc lanp is a device for holding the carbons of an arc light and for maintaining the light constant by means of suitable mechanism. The latter function it is which has given the name “regulator" to such lamps. Two distinct operations must be performed by the regulator; first, it must separate the carbons to produce the light; and second, it must feed these carbons forward as fast as they are consumed, so as to preserve the light from extinction and to keep the length of the arc constant. It may be also necessary, as in the case of focusing lamps, for the regulator to perform a third function; viz., that of keeping the arc constant in position. Moreover, lamps must be capable of operating independently, so as to be used in a circuit with others without being effected by their variations.
In commercial lighting, lamps are usually arranged in series, and the Brush lamp may well serve as a type of this class. In this a ring clutch, surrounding the upper carbon holder, and controlled by an electro-magnet in series with the carbons, lists this holder as soon as the current passes, and thus separates the carbons and produces the light. oreover, this magnet is antagonized by a second one in shunt circuit with it, for the purposes of regulation; since, whenever the arc becomes too long and is in danger of extinction, the increased resistance thus developed throws more current into the antagonizing shunt magnet, enabling it to overcome the main magnet .# so to allow the carbons to feed together. Since the result is due to the differential action of two magnets, one situated in the main and the other in the shunt circuit, such lamps are generally known as shunt differential lamps.
As the positive carbon burns away about twice as rapidly as the negative one, an additional device must be applied in focusing lamps to feed the former twice as fast as the latter. Of arc lamps those used for search-lights are the most powerful. For this purpose the arc is placed in the focus of a parabolic In iri'Ol".
Arc of Contact. In toothed gearing, the arc of the pitch circle which passes any fixed point during the driving contact of two teeth. It should never be less than the distance between the centers of two teeth (the circular pitch of the wheel), or else the driver would cease acting on one tooth before the next tooth was engaged; hence a jump and shock would occur over the space where the driver met no resistance. The arc of contact is usually 11, or twice the circular pitch, and is limited by the condition of not having excessive length to the teeth outside the pitch circle, which would cause unusual obliquity of action of the teeth, and produce greater friction.
Arcola. Town of Lombardy, site of three battles, Nov. 14– 17, 1796, between Bonaparte and the Austrians under Alvinzy, who lost 18,000 men. he French lost 15,000 and became masters of Italy.
Arcot, or ARKAt. City of s. Hindustan, 65 m. s. w. of Madras. Its capture by Clive. Aug. 1751, was the beginning of British power in India. It is the chief town of two districts of the Madras presidency, n. and s. Arcot, which have an area of ab. 12,100 sq. m., and a pop. of ab. 3,700,000.
Arctic Ocean. That part of the sea lying n. of Asia and N. America, and surrounding the N. Pole. It communicates with the Pacific through Behring Strait, with the Atlantic through Smith Sound and the broad passage between Greenland and the Scandinavian peninsula. It contains numerous islands, many of them very large, as Nova Zembla, Spitzbergen, New Siberia, and Wrangle Land, besides the great archipelago n. of N. America. Its shores are icebound. Many navigators have explored it to find the N. W. Passage. Parry reached lat. 82° 45' N. in 1827; Kane attained lat.81° 22' in 1854, and found reason to infer an open sea around the pole; Lockwood of Greeley's expedition, 1882. reached 83° 24′, which is the highest point thus far attained. There are floating masses of ice 200 ft. in height, and ice-fields 100 m. in length. Capt. Ross measured a berg which rose 325 ft. above the water. (See Map, page 88.)
Arctimus. Probably 7th cent. B.C. Greatest of the Cyclic Greek poets. The epics AEthiopis and Destruction of Troy were attributed to him; another is also ascribed to him by some. We have a synopsis of these, and fragments.
Arctisca. See TARDIGRADA.
Arctogaea. Division of the earth's surface, used in considering biological distribution; comprising the Eurasian continent, the Indian and Ethiopic regions, and N. America. This region was as distinctly characterized by its fauna in Tertiary times as now.
Arctoidea (PLANTIGRADA). Section of Carnivora Fissi
pedia, including the families Ursidae (Bears), Procyonidae (Rac
Panda (AElurus fulgens).
coons). AEluridae (Panda of India and Thibet), and Mustelidae (Weasels, etc.).
Arctomyinae (GROUND SQUIRRELS). Sub-family of Sciuridae, including the Arctomys (Marmots), Cymomys (Prairie-dog), Spermophilus (Ground Squirrels), and Tamias (Chipmunk).
Arctomys. The Marmot, Woodchuck, or Ground-hog is the largest member of the Squirrel Family (Sciuridae). See ARCTOMYINAE. They measure up to two feet in length, are plump, have a short bushy tail, low ears, and coarse hair. Cheek pouches are rudimentary, and the pollex bears a flat mail. A. monaa: is the woodchuck proper, which lives solitarily, hibernates in winter, and comes out in spring, whence its use as a weather prophet. Marmots like prairie-dogs generally live in colonies.
Arctopithecini, or HAPALIDAE. Group of Simiadae, including the Marmosets. The nose is of the platyrhine type; the pelage soft and abundant; the tail is long, bushy, and nonprehensile. There are no cheek pouches or natal callosities; the fore-limbs are shorter than the hind. There is no opposable thumb, and the digits are all clawed except the opposable hallux, which has a flat nail. The number of teeth is the same as in man, but there is a praemolar more and a molar less in each series. The molar teeth have pointed cusps. They are S. American monkeys, about as large as squirrels; several species are domesticated and kept as pets. The coloration is variable; many have bands on the tails, and some (Midas) have peculiar crests of hair and whiskers. They are not hardy. The female usually bears twins or triplets after but three months' gestation. The cerebral hemispheres cover the cerebellum. They require insects as food.
Areometer. Instrument for measuring the rarity or density of a liquid. See HYDROMETER.
Areopagus. Hill of Ares or Mars, w. of the Acropolis in Athens; hence the most ancient court of Athens, which met
there. Solon changed its constitution; it became less aristocratic and received the nine annual archons as new members.