dome

dome a roof circular or (rarely) elliptical in plan and usually hemispherical in form, placed over a circular, square, oblong, or polygonal space. Domes have been built with a wide variety of outlines and of various materials.

Early Domes

The earliest domes were probably roofed primitive huts and consisted of bent-over branches plastered with mud. Another primitive form, called a beehive dome, is constructed of concentric rings of corbeled stones and has a conical shape. Ancient examples have been found in the tombs of Mycenae and can also still be seen in the folk architecture of Sicily. Although there is evidence of widespread knowledge of the dome, its early use was apparently restricted to small structures built of mud brick.

Roman and Byzantine Domes

It was the Romans who first fully realized the architectural potentialities of the dome. The Roman development in dome construction culminated in the pantheon (2d cent. AD). The Romans, however, failed to discover a proper handling of the pendentive —the device essential to placing a dome over a square compartment—that was finally achieved by the Byzantine builders of Hagia Sophia at Constantinople (AD 532-37). The other solution to placing a dome over a square was the squinch , which in the form of stalactites was to receive superb expression in Islamic architecture. Under Byzantine influence the Muslims early adopted the use of the dome; one of their first important monuments is the Dome of the Rock in Jerusalem. They often used the so-called Persian or onion dome. The most celebrated example is the Taj Mahal (AD 1630) at Agra, India.

Renaissance Refinements

Both the influence of the Roman Pantheon and of the Byzantine pendentive came to bear on the designers of the Italian Renaissance, and the crossings of many churches of the period were covered by masonry domes on pendentives. Between pendentive and dome a circular drum usually was interposed, serving to give greater elevation and external importance as well as a space for the introduction of windows. By the addition of an outer shell, the exterior came to be independently designed for maximum effectiveness, and the placing of a lantern at the top of this outer shell provided an apex for the entire composition.

Modern Domes

The dome in modern architecture utilizes such materials of construction as reinforced and thin-shell concrete, glass and steel, and plastic. An innovative contemporary approach to the form is the geodesic dome . These are low-cost, geometrically determined hemispherical forms as promoted by architect Buckminster Fuller .

Outstanding Domes

Celebrated examples are Brunelleschi's octagonal ribbed dome for the Cathedral of Florence (1420-36); St. Peter's, Rome, designed by Michelangelo, with two masonry shells (completed 1590), internal diameter 137 ft (42 m); the church of the Invalides, Paris, by J. H. Mansart (1706), 90 ft (27 m); St. Paul's Cathedral, London, by Sir Christopher Wren (1675-1710), 112 ft (34 m); and the Panthéon, Paris, by J. G. Soufflot (1775-81), 69 ft (21 m). The last three domes are built with triple shells, the middle shells serving to support the crowning lanterns.

In the United States the dome of the Massachusetts state capitol, designed (1795) by Charles Bulfinch, established the dome as a distinctive feature for numerous later state capitols as well as for the national Capitol at Washington, D. C. The dome of the latter, however, is of cast iron instead of masonry. The design, by T. U. Walter, has an inner diameter of 90 ft (27 m) and possesses great external impressiveness.

Bibliography

See E. B. Smith, The Dome: A Study in the History of Ideas (1975).

dome
1. Anticlinal structure which plunges in all directions.

2. (volcanic dome, tholoid) A mound of viscous lava, usually rhyolite in composition, which has grown and built up over a vent. The mound of solid lava is covered by coarse, angular blocks which form by chilling and brecciation of the growing dome's surface. The blocks accumulate around the growing dome to produce a scree slope of crumble breccia. Domes can grow by repeated injection of magma into the dome body (endogenous dome) or by repeated eruption of small volumes of magma from the surface of the dome (exogenous dome).

3. (salt dome) A circular or elongate plug, 1–2 km in diameter but extending downwards for many kilometres, formed by the upward movement of buoyant and less dense evaporitic material (commonly halite) into denser overlying rocks. The diapiric movement (see DIAPIR) may be initiated by tectonic thickening.

4. A special form of crystal development characterized by two roof-like faces symmetrical about a plane of symmetry. The faces are repeated once only about an axis of symmetry.

5. See PERICLINE.

6. See ICE DOME.