The redesigned extension to the Tate Modern contemporary art museum in London, launched today, shows Jacques Herzog moving from what would effectively have been a built diagram of stacked boxes - his first attempt of two years ago - into something considerably more smoothly sculpted. It's turning into architecture. He has also abandoned the somewhat quixotic glass cladding to his Mark One scheme - this is to be a south-facing building, remember - in favour of a considerably subtler perforated brick skin.