Australian scientists and a US information technology firm have solved the mystery of the gas bubbles in Guinness stout, which appear to defy the laws of gravity by travelling downward in the famous pint.

The conundrum's solution lies in the shape of the glass and surface effects on its walls, which create a circulating current when the pint is poured. While bubbles rise rapidly through the middle of the glass, they move slowly down its sides. The net effect is of upward movement - as dictated by the laws of physics - although the bubbles visible to drinkers through the glass walls are descending.

Generations have pondered on this ancient phenomenon with intellection fortified by plenty of stout, good company and the smokey air of a good pub. But the Margin doubts that the theories ever invoked "computational fluid dynamics" as used by our friends in the US and Australia. It's your only man, that - the computational fluid dynamics!