Out go the themed rooms and groupings of artists at London's Tate Britain gallery, and in comes a pure, sunlit, chronological walk through British art from 1540 to the present. The world's leading collection of British paintings and sculpture on Monday threw open a permanent gallery so radically refurbished and reorganized that every one of the 500-odd works on display had to be rehung. "What I wanted to try and do was to have a complete chronology that wouldn't be interrupted by exhibitions," said Director Penelope Curtis. She denied that the Tate was "dumbing down" for the average tourist, saying the layout offered better access to everyone from school children to art experts, put works in context with their contemporaries, and would be uncompromised by temporary shows. The "BP Walk through British Art" winds around the perimeter of the building, beginning in 1540 with portraits by the likes of Hans Holbein and Anthony van Dyck, then