first, round the cylinder. in which ease the serew would he called double-threaded. In the ordinary construction of these niaohines, the cylinder itself is hollowed out into a double or triple- threaded screw, and inclosed in a water-tight case, which turns round with it, the space be- tween 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 modifica- tion 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. Tliis is an inunediate 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 are wholly immersed in it, they displace an amount of water of greater weight tlum 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. Ac- cordingly, while bodies heavier than water dis- place, when put into it, their own volume, bodies lighter than water displace, when allowed to iioat on the surface, their own weight of the fluid. Bodies of the same density as water, ac- cording to the [)rinciple of Archimedes, have no tendency to rise or sink in it, for the water dis- placed by them weighs precisely the same as they do. Siniilar statements may be made with re- spect 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 Arcliimedes as applied to the atmosphere. See Hydrostatics.
ARCHIPELAGO, iir'kl-pel'a-go (Gk, npf*- kDmi'oc, archipeUirios, chief sea, originally the .ligean Sea, to distinguish it from the other smaller Grecian waters; from apxi-, archi-, chief + -n-e'Aayo^, pclagos, sea). A term now applied to any definite sheet of water interspei'sed with many islands, but formerly restricted to the -•Egean .Sea (with its islands), which lies between (Jreece and Asia Minor. The islands are usually divided into two groups, the Cyclades and the Sporades. Of the former group Delos, Lyra, Oythnos, Thera, Andros, and Melos are more prominent ; of the Sporades, which belong to Turkey, Rhodes, Cos, Patmos, Samos. and l.einnos are the more signiilicant. 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 Cycl.vdes ; Spo- BADF.s : and inrlividual islands.
ARCHITECTS, iir'kl-tekts, American In- stitute OF. A societv established in 18.57. In 1900 it had 20 chapters, 41(! fellows, 116 associ- ate members, and .54 honorary members.
ARCHITECTURE, ar'ki-tcktfir (Lat. archi- tectura, Gk. apxircurovia, architektonia, from ap^i-, (irchi-, chief -+- tsk-uv, teuton, worker in wood; carpenter, craftsman). In its widest sense this term includes any kind of construction, such as works of military and naval architec- ture and civil engineering; but strictly speak- ing it is building raised by certain iJesthetic qual- ities 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 archi- tect being director of works, and responsible for whatever sculpture and painting was used in connection with .the building. This ancient tra- dition ruled throughout the Middle Ages, and it was not until the Renaissance in the Fifteenth Century that architecture lost its right to govern the other arts. Because architecture had this character of the most universal art, using sculp- ture and painting in subordination, the forma- tion of what we call an architectural st.yle — 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 funda- mentally affected, on the one side by the religious and social elements of society, who.se demands it must meet, and on the other by the material elements such as the influences of climate, of materials of construction and decora,tion, which limit or in certain directions stimulate artistic originality. So that in every age, architecture is a faithful mirror of contemporary soeiet.y, and at once the most material and the most ideal of the fine arts.
Egypt. In respect to historic development, EgA^pt 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 Egj'pt between c. 50(11) and 2500 n.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 nuistaba- tomI)s and all other works of the Ancient Em- pire, have few truly architectural features. The pyramids are a mere mass of material; the tentples and tombs, even when supported by piers, have no moldings, decorations, or details that indicate style. It is only in the iliddle Empire (c.2,500) tiiat the type of columnar temple was evolved, which became the glory of Egj-pt, and that tombs were made — as at Beni-Hassan (see article on Tomb) — where there were columns and other features with a distinct artis- tic 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 ew Empire, especially between c. 1600 and 1400. supplemented l)y the much later constructions of the Ptolemaic Age, almost equal- ly magnificent. Some of the temples were entirely excavated in the rock, like those at Ahu-Simbel (q.v. for illustration) ; others were partly exca- vated, partly structural, as at Deir-el-Bahari ; but the great majority were built entirely in the
