The Heatherwick Effect.(Thomas Heatherwick)

For the past few years, an office development tucked away overlooking an old canal behind Paddington Station, in London, has been attracting clusters of people who come to see a footbridge. Made of steel and wood, and crossing the water in eight short sections, the bridge looks ordinary, but, when a boat needs to pass, it arcs up and back from one side like a scorpion's tail, and folds itself into a neat octagon on the opposite bank.

The Rolling Bridge is the best-known project of the British designer Thomas Heatherwick. Recently, Heatherwick told me that he had started from the premise that most drawbridges look good only when they are extended across the water; ...