Almost 50 years after his famed tight-rope walk between the Twin Towers in New York, Philippe Petit still has his head in the clouds. Above a watchful gala audience in the National Building Museum's voluminous central hall, the 73-year-old French native steps out onto the wire. Up there, Petit takes his time, doing multiple crossings. Even at his advanced age, the high-wire artist continues to defy gravity. IMAGES AND SOUNDBITES