Crowning glory

25th August 2000 at 01:00
Domes may be beautiful and ethereal, but there are also solid, mathematical reasons why people love them. John Stringer and Dinah Starkey investigate.

How many domes can you think of? Apart from the Millennium Dome in Greenwich, domes have a long and spectacular history. St Paul's Cathedral, the Dome of the Rock in Jerusalem, the Taj Mahal, St Peter's in Rome and the Capitol building in Washington all spring to mind. One of the newest is the dazzling metal and glass dome that protects the entrance to Canary Wharf Underground station (shown on pages 10 and 11). But for the first domes, we have to go a lot further back.

Some 6,000 years ago, unknown builders began a circular structure. As they placed circles of stones, one upon another, they began to reduce the circumference of the rings and close the gap in the roof. The finished building had the shape of an old-fashioned beehive. The weight pushed the walls outward, but heavy stones around the base prevented its collapse.

These prehistoric architects had constructed a dome - a shape that contained a large space using relatively little material. Domes have been used by builders ever since for the same mathematical reason. Because a sphere contains the largest volume in relation to surface area of any three-dimensional shape, so a dome, which is part of a sphere, uses the least roofing material to cover the largest space. (A flat roof uses less material, but would not provide the height; a pitched roof gives height, but uses more material.) Many cultures seem to have discovered the technique independently - igloos are perhaps the most familar domes of all. Romans, Christians and Muslims used domes as symbols of power, both spiritual and secular (see over page). Ancient builders in South America, however, never discovered how to build domes or arches.

Domes have been made from many different materials. Sir Christopher Wren's St Paul's Cathedral has an outer dome of timber covered with lead. The US Capitol building in Washington DC (completed in 1863) has a cast-iron dome that is 27m across. The Palazetto dello Sport, built for the 1960 Olympic Games in Rome, is made of concrete. But it was the geodesic dome, invented by Richard Buckminster Fuller in 1947, that changed the modern dome altogether. A geodesic line is the shortest distance between two points across a curved surface. Buckminster Fuller noticed that the surface of a sphere could be divided into triangles by a network of geodesic lines, and he used this idea to create a structure that was roughly spherical, but made up of many light, straight supports. The first such dome to be built was the Dome of Discovery, constructed for the Festival of Britain in 1951.

It is difficult to see why builders should ever stop using domes. They have dominated skylines around the world for 2,000 years, lending importance to the functions and rites that take place beneath them. All kinds of people, from popes to town councillors, have taken advantage of these properties. It seems likely that the practicality of domes, combined with their awe-inspiring beauty, will assure their survival into the next millennium.

* Make a geodesic dome - see The Global Village, centre pages.


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