Stretching from Paris to Le Havre, the Seine river and the valley flanking it afford some of France's loveliest views. The ports, holiday homes and artists' houses, the boats, the washerwomen, the windmills, the open-air cafes, the picnics and the bathing supplied French painting with some of its most iconic images, particularly during the Impressionist era, when painting stepped out of the studio and into the world. It was in this period, as the...