Landscapes reflect the spirit of two nations.
Landscape painting has always been coloured by shades of patriotism. In 17th-century Holland, painters as various as Cuyp, Ruisdael and Rembrandt depicted their flat, fertile, ingeniously irrigated country as a paradise on earth. Sleek fat cattle grazing in meadows of emerald green; windmills silhouetted against skies of pewter; mile after mile of perfectly straight, tree-lined canals: these, to the Dutch, were not just objects of beauty but emblems of their nation itself, salvaged from the sea and freed from imperial Spain.
In Georgian England, John Constable depicted the rosily remembered Suffolk of his childhood as another Arcadia. His paintings are not just images of a truly green and pleasant land; they are also prayers, expressing the fearful hope that his countryside - and, by implication, his country - should never be consumed by the political fires lit by the French Revolution.
Forests, Rocks, Torrents explores two lesser-known tributaries of this long and winding tradition. Its twin subjects are Norwegian and Swiss landscape painting of the 19th century, explored through 51 rarely displayed pictures on loan from the collection of an American lawyer of Norwegian descent named Asbjorn Lunde. One of the first serious collectors to take a deep interest in either field, he has acquired museum-quality works by almost all the most gifted Swiss and Norwegian landscape painters.
As the tide of the show suggests - and as geography and geology dictate - the subjects painted by each group of artists have much in common: snow-capped mountains blued by distance; wide, empty valleys shaped by the thrusting violence of ancient glaciers; dense pine forests; rushing water.
But despite their superficial similarities, Swiss and Norwegian paintings express starkly differing sensibilities: the exhibition is an object lesson in contrasting senses of national identity.