Art: How Turner squared up to the oblong tendency

Late Turner: Painting Set Free
Tate Britain

For the longest time pictures were brick-shaped. Photographs in an album and portraits on the wall were often pre-figured to the Golden Ratio, that pleasing aspect that had mathematical as well as aesthetic qualities.

Turner And The Sea, National Maritime Museum, Greenwich

JMW Turner was the pre-eminent landscape painter in Western art, according to leading Victorian art critic John Ruskin. But the weight and obsession of the artist's canon suggests he was, above all, and with an relentless obsession, a seascape painter.