Sky and Water I
Sky and Water I is a woodcut print by the Dutch artist M. C. Escher first printed in June 1938. According to Escher: "In the horizontal center strip there are birds and fish equivalent to each other. We associate flying with sky, and so for each of the black birds the sky in which it is flying is formed by the four white fish which encircle it. Similarly swimming makes us think of water, and therefore the four black birds that surround a fish become the water in which it swims." This print has been used  in physics, geology, chemistry, and in psychology for the study of visual perception. In the pictures a number of visual elements unite into a simple visual representation, but separately each forms a point of departure for the elucidation of a theory in one of these disciplines. M.C Escher, "Sky and Water I" best exemplify figure ground-reversal.