“An 18th-century savant called Joseph-Louis Lagrange was a pioneer of the study of moving fluids (among many other things), but his ideas outran the computational tools of his day. Only now, with supercomputers available to help with the calculations, is it possible to explore those ideas completely. What is emerging is a picture of fluid dynamics more subtle and more complex than anything dreamed of even a decade ago. The atmosphere and the ocean are, it seems, dominated by invisible barriers that have come to be known as Lagrangian coherent structures. They govern the movement of everything from the trajectories of aircraft to the distribution of pollution, the migration of jellyfish and the tracks taken by hurricanes. They are, as it were, the skeletons of the sea and the air.”