It is because of this that the highest ground in New Orleans, counter-intuitively, is along the riverfront, one of the only areas of town not to flood after Hurricane Katrina.

Their number and strength, their ebb and flood, their play and counter play and above all the laws of their nourishment remain quite unknown to us.

It follows a string of actions by the US to counter a flood of goods that it claims China exports at below market prices.