AR'CESILA'US (Gk. 'ApKecriXaos, Arkesilaos) (n.c. 316-241 ). A Greek philosopher, founder of the Middle Academy. Be was born at Pitane, in ..Eolis; studied philosophy at Athens, first. under Theophrastus. the Peripatetic, and after wards under Crantor, the Academician, and through the latter became acquainted with Pole mon and Crates, by whom, as well as by Crantor, he was profoundly influenced in his philosophic views. After the death of Crantor, he became the head of the Academic school. Arcesilaus marks a reaction against the dogmatism of the Stoic school of philosophy, and an intended re currence to the method and attitude of Plato and Socrates. He denied the Stoic doctrine of a "convincing conception," which he affirmed to be, from its very nature, unintelligible and contra dictory. He also denied the certainty of intel lectual and sensuous knowledge. and recommend ed abstinence from all dogmatic judgments. In practice, he maintained, we must act on grounds of probability. Though Areesilaus confined his activity to teaching by the Socratic method, and wrote nothing, his influence on the future course of philosophic thought was far-reaching. He had clearness of thought, cutting wit, and readi ness of speech; his frank and generous disposi tion charmed his opponents as well as his dis ciples. Consult Zeller, Gesehiehte der griech ischen Philosophic (Leipzig, 1893).
ARCH (Lat. areas, anything curved, a bow, vt-ult. arch). A term used in architecture to designate any curved form that spans an open ing or recess. It may be decorative, as a floral arch; or constructional, as a stone or brick arch. It may be a detached structure, a memorial or triumphal arch; or it may be a part of a large building. A constructional arch may be a false arch, consisting of horizontal courses of masonry, each projecting over the one below it, the edges being chamfered to give the form of the arch without the carrying function; or it may be a true arch, with a keystone, as is usually the case, and may be of the greatest variety of shapes: a primitive triangle, formed of two slanting stones; a tint arch, with wedge-shaped voussoirs; a segmental arch, or very low arch, used often within walls, as a discharging arch, for strength; a usual round or one-centred arch; a stilted arch: a usual pointed or two-centred arch ; a cusped or lobed arch (trefoil, quatrefoil, cinq foil ) ; a horseshoe arch ; a reverse-curve or ogee arch; a basket-handle arch (both three-centred). The arch is formed of voussoirs; the central one is the keystone, the lower onoe, are the springers. The inner side of the arch is the intrados, the outer the extrados. See ABUTMENT; ARCHI VOLT;
SPANDREL.
History.—The supporting power of the arch appears to have been known to most nations of antiquity, but the power was not regarded as artistic. The Egyptians knew the round arch, but relegated it to works of engineering and pri vate architecture; the arch never appears in their temples, tombs, or any other large monu ments. In this they held precisely the position held later by the Greeks. The arch in the As sembly Hall at Priene (time of Alexander). re cently discovered, is supposed to be the only decorative Greek arch found; the few others are in fortifications, etc. But the Babylonians and Assyrians knew and used various kinds of arches in their palaces, tombs, and temples: the false arch; the pointed and the semicircular arches. All the openings in Assyrian palaces were arched. In ancient Italy, the Pelasgic and Etruscan populations used the arch in the same way for secular and sepulchral buildings; for gates, bridges, passages. Only in temple architecture, borrowed from the Greeks of the historic age, was the architrave supreme. This custom was inherited by the Romans, most of whose secular buildings were arched, while their temples were not. But the Romans of the Early Empire did not invent the arcade—that is, an uninterrupted series of arches supported on columns or piers. This was first introduced at Diocletian's palace in Spalato, and developed in early Christian religious architecture. Etruscans, Romans, and early Christians knew only the semicircular arch. But the Persians and Mohammedans, beginning in the Sixth and Seventh centuries, brought into use a variety of other forms: the pointed. the horseshoe, the ovoid. the stilted arches. These forms later penetrated sporadically into Europe, especially where there were political or com mercial relations with the Orient. The pointed arch became, in fact. the favorite Mohammedan form. It was, perhaps, a knowledge of this Oriental usage that suggested to French build ers of the time of the First Crusade the use of this form in vaulting; and thus was laid the basis for Gothic construction, though otherwise there cannot he any connection between the pointed style of the East and Gothic architec ture. In Europe the round-arched style of the Romanesque Period was succeeded by the more flexible pointed style of Gothic. Gothic archi tects produced the greatest number of sub-forms and by-forms of the arch. not all of them pointed. Then the Renaissance returned to the round arch. Modern architects have no style to hamper them, and therefore use all kinds.