15 January 1993
Vol 259, Issue 5093

About The Cover

Fractal pattern formed by small particles floating on a fluid undergoing complicated motion. High particle density (yellow-blue) indicates regions of past compressive surface flow or downwelling. Low particle density (black-red) indicates past upwelling. The pattern geometrically summarizes the long-term, chaotic behavior of typical elements of the fluid surface; it is the strange attractor of a random dynamical system. See page 335. [Image: John C. Sommerer]