Since 1951, Henry Francis du Pont's Brandywine Valley estate, Winterthur, has displayed masterpieces of American decorative arts and furniture to the visiting public. In a rare traveling exhibition, entitled "An American Vision," more than 300 works from the Winterthur Museum's collection of 85,000 objects are featured at the National Gallery of Art. Timed for Winterthur's 50th anniversary, the exhibition remains at the National Gallery through Oct. 6.