“One reason that he was reluctant to relinquish some of his works and declare them completed was that he relished a world in flux. He had an uncanny ability to convey movements—of the body and the mind, of machines and horses, and of rivers and everything else that flows. No instant, he wrote, is self-contained, just as no action in a theatrical pageant nor any drop in a flowing river is self-contained. Each moment incorporates what came right before and what is coming right after. Similarly, he looked upon his art and engineering and his treatises as a part of a dynamic process, always receptive to a refinement by the application of a new insight.”