ART / Exhibitions: Big things in awkward holes: Sculptor Richard Serra faces the Tate's annual space-invader challenge

THE TATE'S Duveen Galleries are an awkward area, half viewing space, half arterial corridor. Each autumn since 1990, the Tate has invited - or challenged - a sculptor to make use of them. This year it's the 53-year-old American, Richard Serra.

Serra's material is heavy steel, milled or forged. His forms are big and plain, the sheet and the block. Indoors or out, the work is designed as a response to, an intervention in, its place: site-specific. For the Tate, Serra plumped for two rectangular blocks of forged and solid steel, 35 and 39 tons respectively, one situated in the middle of each of the otherwise empty galleries - called Weight and Measure, 1992.

This 'seemingly simple' solution was expensive. The sum is not being disclosed, but artist's fee, plus the cost of forging (in Germany), transport and installation must amount to something hefty. There was also a risk of structural collapse. The blocks were so heavy that it was first thought they would have to be delivered by crane through the roof. In the event they were tracked in on rails and are now supported on piles coming up through the floor.

Though it's unlikely that these blocks will become a focus of outrage on the scale of Those Bricks, they won't draw much love either. Much money, much work, few fans: it all amounts to an act of curatorial bravado. For the Tate, this is probably one of the attractions of the project.

You may be expecting something quite gigantic, but solid steel is very heavy, and the work is only equivalent to two large altars or tombs, one 5 ft, the other 5 ft 8 high. Serra abjures any human associations and wants the blocks to be seen, not as isolated objects, but as objects-in-a-place. The dimensions, proportions and positioning of the blocks have been calculated 'to make the volume of the space tangible' so that 'the entirety of the space will be revealed'. The space then is the object.

Does this work? And does it matter? Certainly the things have a power. Any object in the middle of a large, empty hall acquires some focal emphasis. And a very heavy object in a large empty space - as long as you know it's very heavy, and these blocks might to all appearances be hollow - projects a kind of force field. But as for revealing the space as a whole, it's hard to say. One would need to see a range of blocks, with different positions, shapes and sizes to gauge the virtues of this particular solution. And then, the whole experience is rather chimerical. Of course, when you see the official photos of the project, it will look pretty good, carefully symmetrised. But you'll notice another thing: there won't be any people milling around, getting in the way and generally messing up the spatial relationships. For the ideal viewer of this work is actually presumed to be invisible, or at any rate solitary. In a way it is work designed for the conceiving, surveying eye of the artist alone.

At the Serpentine Gallery, Serra has been revealing spaces in another way, with 'drawings' - large rectangular areas of canvas covered all over with a deep, gooey black paint-stick, and fixed to the otherwise white walls. Don't touch them. Their bottom edges run along the floor (which discourages you from trying to see them as pictures) and they occupy various positions around the rooms. And again, there being nothing else they make their presence and their relationship to the whole space felt. But as with the blocks in the Duveen Galleries, there seems to be something circular about the operation. A gallery offers a space to an artist to do some work in. The artist considers the space, and makes some work which reveals this space (ideally). And what's that space again? It's a space that has been made available to an artist to . . . etc.

Serra's outdoor work has more point, since he is working with sites that have some other purpose. And there the work (barring petitions) can be permanent. But galleries of course can't afford to have their spaces made tangible in this way for too long. Which raises the curious question of what becomes of these pieces, once their term is up. The blocks, when they have been gingerly tracked back out of the Tate, will be utterly without raison d'etre, but hard to get rid of. Perhaps they might be placed by the roadside with a memorial plaque: 'These two blocks once revealed the entirety of the space of the Duveen Galleries. Now here they lie. Horseman, pass by]' In all its mystery, that might be a more impressive spectacle than one currently happening at the Tate. Yes, they have a great future.

Tate (071-821 1313) to 15 Jan; Serpentine (071-402 6075) to 15 Nov.

(Photograph omitted)