FEW things tell us more about a culture—what it esteems, what it disparages—than its art.  The plays of Sophocles distill an essence of Periclean Athens just as the paintings of Titian bring us near to the heart of seventeenth-century Venetian culture. Closer to our own day, it is easy to see how Modernist art—with its dissonances and anxious novelties—epitomizes the giddy, Promethean ferment of the early twentieth century. Le Sacre du Printemps or The Wasteland could no more have been composed in 1850 than Les Demoiselles D’Avignon could have been painted then. Such works belong to and help define their time.