first, round the cylinder, in which case the screw would be called double-threaded. In the ordinary construction of these machines, the cylinder itself is hollowed out into a double or triplethreaded screw, and inclosed in a water-tight case, which turns round with it, the space between the threads supplying the place of tubes. It is sometimes found convenient to fix the exterior envelope, and to make the screw work within it, the outer edge of the latter being as close as possible to the former without actual contact, as is shown in Fig. 2. This modification of the Archimedes' Screw receives the name of 'water-screw,' and frequently of 'Dutch screw,' from its use in Holland for draining low grounds. ARCHIMEDES, THE PRINCIPLE OF. One of the most important principles in the science of hydrostatics, so called because the discovery of it is generally ascribed to the Syracusan philosopher. It may be thus stated: A body, when entirely surrounded by a fluid, is buoyed up by a force equal to the weight of the fluid it displaces. This is an immediate consequence of the principles of fluid pressure, which prove also that the line of action of the upward force is vertically through the centre of gravity of the displaced fluid. When bodies lighter than water wholly immersed in it, they displace an amount of water of greater weight than their own, so that if left free to adjust themselves, they rise to the surface and float, only as much of their bulk being submerged as will displace a quantity of water weighing the same as themselves. cordingly, while bodies heavier than water displace, when put into it, their own volume, bodies lighter than water displace, when allowed to float on the surface, their own weight of the fluid. Bodies of the same density as water, according to the principle of Archimedes, have no tendency to rise or sink in it, for the water displaced by them weighs precisely the same as they do. Similar statements may be made with respect to bodies surrounded by other liquids or by gases-e.g., the atmospheric air. The buoyancy of balloons is an illustration of the principle of Archimedes as applied to the atmosphere. See

HYDROSTATICS.

are

Ac

ARCHIPELAGO, är'ki-pěl'à-go (Gk. px hayoç, archipelagos, chief sea, originally the Egean Sea, to distinguish it from the other smaller Grecian waters; from apx-, archi-, chief + méλayos, pelagos, sea). A term now applied to any definite sheet of water interspersed with many islands, but formerly restricted to the Egean Sea (with its islands), which lies between Greece and Asia Minor. The islands are usually divided into two groups, the Cyclades and the Sporades. Of the former group Delos, Lyra, Cythnos, Thera, Andros, and Melos are more prominent; of the Sporades, which belong to Turkey, Rhodes, Cos, Patmos, Samos, and Lemnos are the more significant. They are of volcanic origin, have a healthful climate and beautiful scenery. These islands have played a great part in the course of Greek history, giving to the world poets and philosophers. For a more detailed description, see CYCLADES; SPORADES; and individual islands.

ARCHITECTURE, är′ki-těk'tûr (Lat. architectura, Gk. apxITEKTOVía, architektonia, from άpx-, archi-, chief + TEKTWV, tektōn, worker in wood; carpenter, craftsman). In its widest sense this term includes any kind of construction, such as works of military and naval architecture and civil engineering; but strictly speaking it is building raised by certain æsthetic qualities to the rank of art, as distinguished from purely utilitarian or mechanical building. Its name shows that it was regarded by the ancients as the chief art, comprising all others, the architect being director of works, and responsible for whatever sculpture and painting was used in connection with the building. This ancient tradition ruled throughout the Middle Ages, and it was not until the Renaissance in the Fifteenth Century that architecture lost its right to govern Because architecture had this the other arts. character of the most universal art, using sculp ture and painting in subordination, the formation of what we call an architectural style-like the Greek or the Gothic style-was a complex and gradual process. For architecture, being one of the earliest and most constant expressions of civilization, is not the artificial product of the free conception of a few artists, but is fundamentally affected, on the one side by the religious and social elements of society, whose demands it must meet, and on the other by the material elements such as the influences of climate, of materials of construction and decoration, which

limit or in certain directions stimulate artistic originality. So that in every age, architecture is a faithful mirror of contemporary society, and at once the most material and the most ideal of the fine arts.

EGYPT. In respect to historic development, Egypt and Babylonia-the valleys of the Nile, and of the Tigris and Euphrates-are rivals for seniority in the field, which they seem to have held alone for one or more thousand years, while the rest of the world went without architecture. It is true that the early monuments of Egypt between c.5000 and 2500 B.C. are works of mere building rather than of art. The pre-pyramidal tombs; the pyramids themselves; the primitive chapels or temples connected with them (such as the "Temple of the Sphinx"); the early mastabatombs and all other works of the Ancient Empire, have few truly architectural features. The pyramids are a mere mass of material: the temples and tombs, even when supported by piers, have no moldings, decorations, or details that indicate style. It is only in the Middle Empire (c.2500) that the type of columnar temple was evolved, which became the glory of Egypt, and that tombs were made-as at Beni-Hassan (for illustration, see ROCK TOMB) where there were columns and other features with a distinct artistic character-such as the 'Doric' type and the clustered-palm type. The destructive invasion of the Shepherd Kings has forever obscured this second stage of Egyptian architecture, and for a knowledge of its possibilities the Golden Age is that of the New Empire, especially between e. 1600 and 1400, supplemented by the much later constructions of the Ptolemaic Age, almost equally magnificent. Some of the temples were entirely excavated in the rock, like those at Abu-Simbel (q.v. for illustration); others were partly excavated, partly structural, as at Deir-el-Bahari: but the great majority were built entirely in the

ARCHITECTURE.

open and of stone masonry. A few are sepulchral temples, such as the Rameseum at Medinet Abu (q.v. for illustration), but with these exceptions they are purely temples to the gods. Each temple of the usual type was approached through a long avenue of sphinxes or statues, was preceded by an immense façade of pylons connected with an encircling wall, with an open columnar court, at the opposite end of which was a hall of columns forming the prelude to the dark inner sanctuary. This is undoubtedly the earliest conception of a large columnar interior in architectural history, and though its proportions may be heavy, the composition was artistic and imposing, and botn sculpture and color were used with architectural details to enhance the effect. Karnak, Luxor, Edfu, and Philæ are the inasterpieces over a period of some fifteen hundred years (for illustrations of EDFU and LUXOR, see those titles). No vaults, arches, or piers were used in any part of this architecture only the straight lintel and column. The heavy columns, of so many forms as to rebel at any classification by orders, were placed very close together, so that the effect was not one of spaciousness.

BABYLONIA AND ASSYRIA. Babylonian architecture is less known, but there is enough information about it to show that it reached its full development as an art long before the Egyptian, and that while the latter remained isolated, Babylonia stood at the head of a long architectural genealogy; for Elam and Assyria literally copied it; Persia, the Hittites, and Phoenicians and other nations borrowed from it, and its influence was felt even to China and India. There could be no sharper contrast than that which exists between these two primitive architectures. In Babylonia vaults and arches were used in place of straight lintels and flat ceilings, and there were no long lines of columns, and consequently no larger interiors than could be secured by the span of a single dome or tunnel vault; brick was used in place of stone, thus increasing the heaviness of walls and proportions. The Babylonian style appears to have existed at least 6000 years B.C., and to have lasted without essential change until the time of Nebuchadnezzar. The temples had no large interiors, but were stepped pyramids, remarkable mainly for their great height, their external mass, and the brilliant coloring of their receding stories, faced with glazed tiles. Only in the royal palaces did the Babylonians excel, creating a type which the Assyrians developed with numerous halls and chambers grouped around three main courts. The palace at Tello, the temples at Erech and Ur, give the usual types; but the excavations at Nippur and Babylon are disclosing other splendors. Meanwhile the better preservation and more thorough study of the Assyrian ruins enables to judge somewhat of the details of the earlier style. The temple observatory and the palace of Sargon at Khorsabad were destroyed by some great catastrophe-probably by fire-when they were still occupied, perhaps at the time of the fall of Nineveh; and not only their plan, but also a large part of their structure and decoration in sculpture and color, can be reconstructed. the Babylonian-Assyrian ruins suffer by comparison with the Egyptian, from their poor preservation, largely due to their easily disintegrated brickwork.

Still,

HITTITES AND PHOENICIANS. The Hittites, the rivals of both Egypt and Assyria, were great builders; like the Egyptians, they used stone and were constructors of fortresses. Of their temple architecture little is known; but their palaces-one of which has been excavated at Senjerli and another at Boghaz-Köi-appear to have been of a type similar to the Assyro-Babylonian. Their works were scattered from the confines of Assyria to the Syrian coast and as far northwest as the interior of Asia Minor. Of the architecture of the Phoenicians very little remains; they also built in stone, and like the Hittites used at first the Cyclopean and polygonal masonry. The great fortifications and ports of Arvad, Tyre, Sidon, and the colonies of Africa and Italy show that the utilitarian side of this architecture was more developed than the religious; for the temples themselves were but small shrines, none of them equaling, apparently, the temple of Jerusalem in size and splendor, though the actual work on this temple was done by Phoenician artisans and artists.

THE GEAN STYLE. It was the migrating Pelasgic tribes of Asia Minor, the Mediterranean islands, Greece and Italy, whose works formed the first link between these early architectures of Western Asia and that of the pre-Hellenic and Hellenic world, forming what is called the Egean style, which flourished mainly between c.2000 to 1000 B.C. The cities of Crete, as Cnossus, and of other islands, of Troy and other cities in Asia Minor, Tiryns, Mycenæ, Argos, and others in Greece beside many early Italian cities, such as Norba and Lignia, show how impressive and rugged a style of construction was combined by these races with a delicate and varied decoration, especially in the bee-hive domical tombs (Mycenæ, Thoricus, Vaphio, etc.) in the royal palaces, which were as important in their way as those of the Assyrian kings.

PERSIA. The second connecting link was Persia. Its great palaces and tombs at Susa, Persepolis (q.v. for illustration), Meshed Murgab, and Pasargada, with monuments from Cyrus to Artaxerxes, show the influence of Egypt in their great columnar halls-though they are far more spacious and light than the Egyptian-of Babylon and Assyria in the use of brickwork, sculptured colossi, and friezes of reliefs in the curious double-animal capitals and the enameled tiles. From Lycia and the Greeks of Asia Minor came the high stone basements for their structures, the flutings of their columns, and many details. The hall of Xerxes at Persepolis is more than twice the size of the great hall at Karnak, and shows how such columnar interiors, once introduced into Western Asia, were appreciated and developed. The later dynasties of Persia-both Parthian and Sassanian-threw off many of these foreign elements in a tendency to return to the brickwork, the domes, vaults, and arches of truly Oriental type, as can be seen in the palaces at Sarbistan, Firuzabad (q.v. for illustration), and Ctesiphon.

GREECE. Meanwhile, even before the rise of Persian architecture, the Greeks had originated the Doric and Ionic (for illustration, see these titles) orders in all their essential features. The temple, which is the one central figure in this architecture, appears to have developed out of the main hall of the Pelasgic royal palace, as it is seen in Crete, Troy, Tiryns, and Mycena,

through a middle stage of crude brick walls, wooden columns, architraves, and gables, with terra-cotta revetment and decoration, into the final type of stone temple which was reached as early as the Seventh Century B.C. It is in Sicily and Southern Italy, that the earliest works of the Doric style are to be found (Syracuse, Selinus, Metapontum), while the earliest Ionic temples were in Asia Minor, at Samos and Ephesus; but these hardly rival the Doric in age, and their ruins do not belong, like those of the Doric temples, to the primitive structure. The normal type of these temples was a building raised on a three-storied basement, and consisting of one main cellachamber (naos) usually supplemented at one end by a smaller chamber (opisthodomos), and preceded at the other end by a pronaos, the whole being surrounded by a colonnade on all four sides, surmounted by an entablature and crowned on the two short ends by gables. Although using, Greeks did not plan great columnar halls or courts like those of the Egyptian temples, but relied on external effects almost entirely; on refined beauty of outline and proportion. Never, until the period of decadence, was there any attempt at impressive size or picturesqueness. The Doric style was heavy in proportion and plain in ornament, in comparison with the Ionic, but provided for more considerable figured sculpture in the friezes, metopes, and gables. It prevailed at first over nearly the entire Hellenic world, gaining gradually in delicacy and lightness, especially when handled by artists with Ionian blood, as was the case at Athens, which contains in the Parthenon and the Theseum the two finest works of the developed Periclean Age, though they are almost rivaled by some Italian and Sicilian works, such as the temples of Pæstum (q.v. for illustration) and Girgenti. At this time other works, such as the Propylæa at Athens, became worthy to stand beside the temples, and here the two styles-Doric and Ionic-were for the first time combined. The originality and daring of this Attic school were also shown in the Porch of the Maidens in the Erechtheum (q.v. for illustration). The succeeding Age of Praxiteles, and the Alexandrian Period brought even slimmer Doric proportions, increased favor for the more decorative Ionic style (temples of Miletus and Ephesus), invention of the still richer Corinthian (q.v. for illustration), and the development of colossal forms of public, civil, and sepulchral architecture (such as the propylaas, theatres, odeons, stoas, the altar at Pergamus, the mausoleum of Halicarnassus), in which Oriental splendor and love of the colossal overruled Hellenic

reticence.

ROME. This prepared the way for Roman architecture. In the Royal and Early Republican Periods, Rome had followed the Etruscan and Latin types: wooden temples with terra-cotta revetments in the Doric style and civil structures of stone, vaulted and arched. These two types remained fundamental, except that before the close of the Republic stone had replaced wood and terra-cotta in the temples, the Ionic style had been introduced by Greek artists, and the Greek orders, with their lintels and columns, had been added as a surface decoration and framework to the constructive arcades in secular buildings. The Greek spirit informed the Roman in the sphere of art, without conquering it, for ordi

narily it is not difficult to distinguish the two styles. The Roman temples are not peristyles, but in antis, with a very deep colonnade in front, and this alone would be sufficient to make their appearance differ fundamentally, even without the substitution of the heavier Corinthian and composite forms for the Doric and Ionic. But the true nature of Roman architecture appears in its civil structures: in theatres and amphitheatres, aqueducts, triumphal arches, palaces, villas, and, above all, in the baths and thermæ. The Roman genius for composition shines in such great combinations of structures as the Villa of Hadrian, the Palace of the Cæsars, the Forum of Trajan (q.v. for illustration), and the Baths of Caracalla and Diocletian. And the great vaulted interiors of some of these buildings, such as the Basilica of Maxentius and the Baths of Caracalla, surpass anything previously conceived of in architecture. With the Greeks, architecture had been plastic; with the Romans, who developed the ideals of the Alexandrian Greeks, it was pictorial. It also combined, in the highest degree, utility and comfort with showiness and imposing and costly appearance. The whole civilized world was filled with the monuments of this art—which fell heir to the cultures of both the Orient and Greece.

EARLY CHRISTIAN. When religion again became paramount, with the advent of Christianity, architectural law and development coincided with the building and decorating of churches. The scheme involved the development of large interiors for a crowd of worshipers quite a different problem from that confronting pagan architects. The public basilica of the Roman fora and the basilical halls of private houses offered models for such a type. The early Christian architecture, with thin brick walls, wooden ceilings, and long colonnaded interiors, at first prevailed everywhere, the poverty of architectural form and detail being partly concealed by rich mosaic and marble ornamentation.

BYZANTINE AND BASILICAL STYLES. But as early as the Sixth Century the Oriental constructive spirit asserted itself once more in the Hellenic Provinces, and two sharply contrasted styles henceforth flourished side by side: the Byzantine domical architecture in the Empire of the East, and the wooden-roofed Latin basilical architecture in the West, especially in Italy. Rome, Ravenna, Salonica, Central Syria, North Africa, are full of early basilicas. Constantinople with Saint Sophia (q.v. for illustration) and others, Ravenna, Greece, Asia Minor, Syria possess numerous Byzantine churches. While the Byzantine style underwent, in the course of sueceeding centuries, certain changes, such as the heightening of the drums of the domes, the decoration of the exterior with marble or alternate courses of stone and brick, the use of accessories like porches, colonettes, etc., these differences were of minor importance.

MOHAMMEDAN. In the West, on the contrary, the new civilization resulting from the awakening of the northern races in the Eleventh Century and their fusion with the old stock, created for itself a new architecture of which the first phase is called Romanesque, the second Gothic. But before describing its characteristics, a phase of Oriental architecture which arose in the meantime must not be omitted-that of the Mohar