By its nature, dance poses unique challenges for scholars. There’s no universal notation system, and the various ways we have to document it are incomplete and unreliable. There is no full way to capture the presence of dance except through dance itself. This tension—between dance and the representation of dance—is always at the heart of dance; dancers feel it, too, and so do the people who watch dance and the people who write about it. The recent exhibition “Hymn to Apollo: The Ancient World and the Ballets Russes” at NYU’s Institute for the Study of the Ancient World reminded me how intriguing this tension is.