“I don’t paint so that people will understand me,” said the English genius of Romanticism, Joseph Mallord William Turner, “I paint to show what a particular scene looks like.” That meant a capture of the elemental—wind, mist, and all manner of light, the refractions on Venetian lagoons, the mystical beauty of the English countryside, the orange haze of seascapes. Though Turner sold many paintings throughout his life, his watercolor experiments were kept to himself. This major retrospective presents 60 watercolors and 10 oil paintings, some of which have never been displayed in France. —E.C.