At 2.27am on October 17, a brand new landmark joined the London skyline. The British Airways London Eye is the largest observation wheel in the world, and offers unrivalled views across the whole of London. It is due to open on February 1.
Wheels like the London Eye have a long history. They may date back to water wheels 2,000 years ago in the Far East. These "undershot" wheels (turned by water flowing under them) provided thrilling but risky rides for children. In 1620, the traveller Peter Mundy reported seeing in Bulgaria a "great wheel on whose circumference are fastened little seats, wherein the children being sat the wheel is put about, they all going round horizontal wise". This was a "whirligig"; the vertical version was called an "up-and-down" and there was one - with "people on flying coaches" - at London's Bartholomew Fair in 1699. Swings were attached to four pairs of arms, rotated by hand. Unfortunately, the wheel broke in 1754, and was burnt by the disappointed crowd.
The London Eye is not a Ferris wheel - the fairground wheel named after its inventor, the American engineer G W G Ferris, who died in 1896. These are supported on both sides by strong frames. The London Eye hangs from a single hub that weighs 330 tonnes - 20 times more than the bell Big Ben.
The London Eye, like the Eiffel Tower (1889) and the Chicago Ferris Wheel (1893) is meant both to celebrate and entertain. At 135 metres high, it is taller than Big Ben's tower (976m) and St Paul's Cathedral (108m). It dwarfs previous wheels - the Texas Star (1985) in the State Fairground, Dallas, at 65 metres and the Technocosmos in Kobe, Japan, at 85 metres.
Architects Julia Barfield and David Marks conceived of it as a structure that allowed participation. Their idea was developed in response to a competition in the newspapers in 1993, asking for a landmark to celebrate the millennium. They decided on an experience - something that everyone could enjoy. A wheel is a human invention - something that doesn't exist in nature. Placing one on the South Bank of the Thames, where the 1951 Festival of Britain was held, and midway between the old cities of London and Westminster, and over the river - like a water wheel - makes it possible to see the whole of London for the first time.
The engineering involved pushes technology to the limits; the London Eye is the largest circular object to be lifted to the vertical. It is supported on one side only, at three points - two under pressure and one under tension. The structure has been designed to avoid resonating with the wind, which - if it were to set the frame vibrating - could twist it like cardboard, as it did with the bridge at Tacoma Narrows over the US State of Washington's Puget Sound. The 32 pods - entirely glazed from double curved glass, heated and air conditioned and with their own sound systems - will offer the best view in London.
More than two million people are expected to take the 30-minute ride every year, travelling at a quarter of walking speed. The London Eye has planning permission to remain standing for five years, but it will be 50 before it needs major servicing. By then it may have become a welcome fixture on the London scene, "up-lifting people" in David Marks's words, "and putting smiles on faces".
CYCLES AND PLANETS
At the turn of the millennium, it is appropriate that we think about cycles and circles, about endlessness and repetition.
All of life moves in cycles. Our lives are cycles from birth to death, and we live in a world that is ordered by day and night and the endless seasons. Cycles manage to combine novelty and predictability in a way that defeats boredom. Day follows night, and spring follows winter. At a deeper level, everything about us is recycled. The water we drink has been a constituent of bodies other than ours; the air that we breathe contains molecules that were once breathed by Jesus, by Boadicea and by Napoleon. Crops grow in cycles - in circles and rhythms that take the carbon dioxide we breathe out and magically combine it with water to produce the food we eat, many of the clothes we wear and even the furniture we use.
To Claudius Ptolemy, the Greek astronomer and geographer who worked in Alexandria around the year 150AD, there was a pleasing symmetry about his model of the heavens. The Moon orbits the Earth, obviously; and since the Greeks believed that a circle was the perfect form of motion, it was only to be expected that the planets - among which Ptolemy included the Sun - revolved around us too.
Pythagoras had already found a relationship between musical notes and mathematics; he had suggested that it should be possible to calculate the orbits of the planets (which they pictured as being carried round the Earth on crystal balls) by relating them to the musical intervals.
Pythagoras found that the chords which sound most pleasing to the western ear correspond to exact divisions of a vibrating instrument string by whole numbers. Pythagoreans argued that all the dimensions of nature would be simple numbers, too. It should be possible to relate the orbits of the heavenly bodies to these musical intervals.
This was called the Music of the Spheres. This model of the planets moving in perfect circles around the central Earth was to last for 1,400 years. But in 1632 Galileo first published his observations that the Sun - and not the Earth - was the centre of the solar system; then, in 1609, Johannes Kepler, in his Dialogue, demonstrated that the orbit of a planet is only roughly circular - it is in fact a broad ellipse with the Sun slightly off-centre.
The Sun, the Moon, the Earth and the stars and planets are spheres. Every object has a field of gravity that originates in its very centre. The bigger the object, the stronger the pull of its gravity. When the heavenly bodies were forming, matter was pulled towards their centre. This pull was equal in all directions. The matter formed a sphere.
Similar forces are at work on a bubble. The thin skin of a bubble is under pressure from the air inside. This pressure is equal in all directions - so a free bubble will always be a sphere. Bubbles formed in frames take up shapes that make the pressure equal all over the skin.
INVENTING THE WHEEL
Imagine a civilisation without the wheel. The Inca civilisation rose, prospered and fell without wheeled traffic. Bereft of a written language, ignorant of the arch and unable to span any gap wider than the longest lintel, the Inca built roads and suspension bridges wide enough for 12 to walk abreast that never echoed to the rumble of a cart wheel. Yet the potter's wheel had been known in Mesopotamia five thousand years before. By 2800BC, wheels had been attached to sleds and rafts, making it easier for animals to pull loads. War chariots rode on solid wheels.
Wheel and axle together are a rotating lever. A short movement of the axle produces a greater movement of the wheel. The wheel, because it has a small 'footprint' compared with a sledge or even a roller, reduces friction between it and the ground. Loads move more easily. By 2000BC, spoked wheels were in use in Asia Minor and Persia. By lightening the unsprung weight of a cart or carriage, the spoked wheel ensured that more of the energy needed to pull the vehicle went into moving it forward. Vehicles became faster.
The same principle is still in use today in the lightweight alloy wheels of modern cars. The bicycle wheel in Victorian times was light in weight but stiff in structure because the spokes were in tension. The pneumatic tyre enabled the wheel to grip the road and damp the bumps - and slots or "sipes" cut in its surface squeezed water from the tread, increasing grip on rainy days. For faster cars, five-stud wheels ensured that there was no natural split line across the centre of the wheel - copying the strong structure of five-legged starfish.