Dawn Ades and other authorities in the field discuss the paintings as The Enigma of William Tell, in which Dali experimented with anamorphosis, the perspectival distortion that produces on the canvas elongated forms demanding an oblique viewpoint. They also note his interest in other more conventional forms of perspective and their sources in both Dutch and Italian art. They study his development of the famous double image, the "paranoiac-critical method" that produced images that could be "read" in multiple ways, as seen in his Apparition of a Face and Fruit Dish on a Beach or Impressions of Africa. And they reveal his fascination with optical effects and three-dimensional illusions that is