Arcesilaus

(a ˙ r-ses-i-lā´us), a Greek philosopher, the founder of the second or middle academy, was born about 315 B.C. , died 239 B.C. He left no writings, and of his opinions so little is known that it has been doubted whether he was a strict Platonist or a sceptic. The New Gresham Encyclopedia - Volume I Part 2. IMG:4014330425200354480_image083.jpg:Parts of an Arch Parts of an Arch a. Abutments. i. Impost. p. Piers. v. Vou oirs or arch-stones. k. Keystone. s. Springers. In. Intrados. Ex. Extrados. IMG:4014330425200354480_image084.jpg:Lancet and Horse-shoe arches Arch , a structure composed of separate pieces, such as stones or bricks, having the shape of truncated wedges, arranged on a curved line, so as to retain their position by mutual pre ure. The separate stones which compose the arch are called vou oirs or arch-stones ; the extreme or lowest vou oirs are termed springers , and the uppermost or central one is called the keystone . The under or concave side of the vou oirs is called the intrados , and the upper or convex side the extrados of the arch. The supports which afford resting and resisting points to the arch are called piers and abutments . The upper part IMG:4014330425200354480_image085.jpg:Segmental and Semicircular arches of the pier or abutment, where the arch rests—technically where it springs from —is the impost . The span of an arch is in circular arches the length of its chord, and generally the width between the points of its opposite imposts whence it springs. The rise of an arch is the height of the highest point of its intrados above the line of the imposts; this point is sometimes called the under side of the crown , the highest point of the extrados being the crown . Arches are designated in various ways, as from their shape (circular, elliptic, .), or from the resemblance of the whole contour of the curve to some familiar IMG:4014330425200354480_image086.jpg:Ogee and Equilateral arches object (lancet arch, horse-shoe arch), or from the method used in describing the curve, as equilateral, three-centred, four-centred, ogee, and the like; or from the style of architecture to which they belong, as Roman, pointed, and Saracenic arches.— Triumphal arch , originally a simple decorated arch under which a victorious Roman general and army pa ed in triumph. At a later period the triumphal arch was a richly-sculptured, ma ive, and permanent structure, having an archway pa ing through it, with generally a smaller arch on either side. The name is sometimes given to an arch, generally of wood decorated with flowers or evergreens, erected on occasion of some public rejoicing, .