Allan Bridge has finally done it - escaped the orbit of potential to bring out solid, finished, fascinating work in a show at the International Monetary Fund.

The work is five machines - pedestal-mounted Plexiglas boxes holding 9,000 clear marbles and a concatenation of brass gears, solenoids, wires, slides, springs, traps and clocks. They are clean, hard, lucid and good to look at. They're intriguing without being obscure or hostile, which is to say they have also escaped the orbit of the avant-garde.

Bridge calls them "mortality machines" and their function, conceptually, is to die. Prompted or doomed by our turning of wheels, our failure to turn them, our pulling of slides or plugs, the marbles fall from top to bottom of the machine, never to be restored to their original machine unless we tear the machines apart.

They provoke, with Bridgean perverseness, insoluble questions of curatorship, permanence and aesthetic certainties. Bridge himself says they have "a tragic principle," the implication being that a series of inevitable though fated acts leads to death, the requisite pride being in the idea of art itself.

We've been waiting for these machines for years, ever since a chunk of Washington's art world decided that Allan Bridge was some kind of genius. Mad? Unsung? Evil? Frustrated? His recent painting seemed aimed at cornering a smaller and smaller aesthetic market. But the machines no longer trade on promise.

The show is open from 9 to 5:30 daily (not Saturday) at the IMF, through July 8.