A confident nation has been converted and liberated by modern art

Earlier this week, the Queen inaugurated a pier. It wasn't supposed to be a pier, it was supposed to be a bridge, but as yet Sir Norman Foster's futuristic "blade of light" falls too far short of the South Bank to qualify properly for that description. It was, you might have thought, the perfect opportunity for the mockers and nay-sayers to come out in force, another of those grand projects that end up over-budget and behind schedule. And yet the dogs didn't bark, because the incomplete Millennium Bridge was bathed in the powerful gleam of pre-emptive success given off by Tate Modern - the stunning conversion of Bankside Power Station into Britain's first major gallery of modern art.

When it is finally finished the Millennium Bridge will complete a new ley line in the city - one of those powerful axes along which new forces and compulsions flow. The alignment it will create has a highly suggestive symmetry: on the north bank, Wren's great monument of reconstruction, St Paul's, and on the south, facing it square on and giving a cubist echo of its balance of vertical and horizontal forces, Gilbert Scott's Bankside, now converted by the Swiss architects Herzog and de Meuron into a place of contemplation for a more secular age. In years to come, this is where many people will go when they seek something that transcends the mundane.

And already the new building is pulling off some minor miracles. It has generated patriotism in the most unlikely places; last Sunday night the artist Tracey Emin could be seen on television confessing that the new building made her proud to be British: she spoke with the uninflected sincerity of a Conservative parliamentary candidate.

At the same time, those for whom patriotism and a taste for modern art have usually been incompatible have also succumbed to the building's flair. Newspapers and commentators whose stock in trade is a mockery of the kind of conceptual work Tate Modern showcases so brilliantly have greeted the new gallery.

Both recognise what - setting aside some overheated hype about Cool Britannia and Young British Artists - is a genuine movement of popular conversion, one that has its missionary outposts all over the country. In Walsall a new gallery creates a public space specifically designed to proselytise for modern art. In Gateshead the artist Anthony Gormley overcomes initial suspicions to create the Angel of the North, a landmark sculpture now enthusiastically adopted by local people. And, upriver from Bankside, what you might describe as the biggest installation work ever - the Millennium Wheel - steadily ratchets up the capital's profile. In America, there is concern that London has supplanted New York to become the world's style-setting centre of artistic creativity, where even the curating of exhibits, such as those in the new Ondaatje wing of the National Portrait Gallery, garners praise.

The obvious contrast to these triumphs of imagination is the Dome. By the standards of any commercial attraction, the Dome is a runaway success - no theme park operator would dream of matching its attendance figures. But it remains inextricably fixed in the public mind as a failure, and a symptomatic one at that.

Where the Wheel and Bankside are seen as essentially non-governmental, the Dome is messily political; where the Dome has designs upon us, the Wheel and Bankside seem to have none. Where the Dome is didactic and worthy, Tate Modern and the Wheel are suggestive and liberating: they tap into a new popular assurance about the enigmas of contemporary art and the exhilaration of fine architecture, a confidence that these are not frauds upon the public but gifts to them. And where the Dome nags us to celebrate as though it were a civic duty, Tate Modern and the Wheel simply inspire us.