The landscape paintings of Alfred Sisley (1839-99) occupy an inviolable position in the history of early Impressionism. His depictions of the Thames at Hampton Court. the Seine in flood, the snow-bound suburbs of Paris are indispensable to an account of Impressionist landscape painting in the 1870s. Indeed, they are so fundamentally representative of our notion of what constitutes 'pure' Impressionism. that the re-evaluation of the movement in recent years has often left Sisley stranded outside it. This has greatly added to the comparative neglect of his work. He is famous but not known, admired but little studied. Many accounts of Impressionism treat him perfunctorily; assessments run on the comfortable premise that he was a marvellous painter for two or three years but became a victim of his style and collapsed into an irreversible decline...