One enters the Sunley Room to find a space in which time stands still and calm reigns. It would be easy, and yet wrong, to dismiss much of what is on show as sterile “optical art”. Arcadia shows Riley to possess the same fascination with composition and colour harmony as a Fauvist Matisse. Composition with Circles 7 emerges as the highlight, allowing one’s eye to happily weave in and out of its delicately constructed ebb and flow of lines at a gentle pace. The carefully selected works on show here intrigue and tease rather than jostle for attention. Riley provides a soothing break from the rigours of much of the National’s stock.