Robert Smithson once dreamed of a floating island that would circle Manhattan. “Thirty-five years after the now-deceased Smithson drew it, his island artwork has become reality: a 150-ton flat-bottom boat full of dirt planted with trees, shrubs and grass. Through Sept. 25, tugboat captain Bob Henry will spend at least 12 hours a day pulling ‘Floating Island’ up and down the East and Hudson rivers around Manhattan.”