An observation wheel is a large slowly-rotating vertically-oriented structure carrying enclosed passenger cars or pods along its circumference. Although observation wheels are often described as Ferris wheels, the two differ in a number of significant respects:
Ferris wheels often have open cars or, in small wheels, individual bucket seats. An observation wheel has completely enclosed cars.
A Ferris wheel's passenger cars hang within the wheel's frame and are usually kept level by gravity. An observation wheel's cars are mounted on the outside of the frame and are stabilised mechanically.
A Ferris wheel is supported by two towers on each side of the axle. An observation wheel is supported by a single A-frame mounted on one side.
The world's most famous observation wheel is the London Eye in England. Its great popularity has led to a number of other cities, including Birmingham, Moscow, Las Vegas, Shanghai and Singapore proposing to erect similar wheels. The Birmingham one is perhaps the most unusual, as it would be fixed in place while the pods would move around the circumferance along a rail track. Las Vegas and Singapore are competing to build the highest in the world, at 182m (600 ft) and 170m (557 ft) respectively. Both are projected to open in late 2005.
