Movies are made out of darkness as well as light; it is the surpassingly brief intervals of darkness between each luminous still image that make it possible to assemble the many images into one moving picture. Without that darkness, there would only be a blur. Which is to say that a full-length movie consists of half an hour or an hour of pure darkness that goes unseen. If you could add up all the darkness, you would find the audience in the theater gazing together at a deep imaginative night. It is the terra incognita of film, the dark continent on every map. In a similar way, a runner's every step is a leap, so that for a moment he or she is entirely off the ground. For those brief instants, shadows no longer spill out from their feet, like leaks, but hover below them like doubles, as they do with birds, whose shadows crawl below them, caressing the surface of the earth, growing and shrinking as their makers move nearer or farther from that surface. For my friends who run long distances, these tiny fragments of levitation add up to something considerable; by their own power they hover above the earth for many minutes, perhaps some significant portion of an hour or perhaps far more for the hundred-mile races. We fly; we dream in darkness; we devour heaven in bites too small to be measured.