BATH.- “It was unique when it opened in 1961, and it remains unique today.” This is how Richard Wendorf, the director of an unusual museum on the outskirts of Bath , describes the only public collection of American art to be found beyond the boundaries of the United States . The American Museum in Britain, which will celebrate its 50th anniversary in 2011, contains over 15,000 items devoted to the decorative arts of America: fancy gowns and Shaker furniture, an extensive collection of native folk art, important holdings of early maps charting the discovery and exploration of the Americas, and one of the largest and finest quilt collections in the entire world. “Portrait paintings and Grandma Moses, painted furniture and Chinese export porcelain – you will find it all here on top of Claverton Hill.” For the past 50 years the American Museum in Britain has informed its visitors about the cultur