The song of the bridge: a dramatic demonstration of the properties of stainless steel and glass is developing a personality of its own.

It's said to be the biggest musical instrument in the world but, in a sense, that's incidental. The main purpose of the bridge which spans the atrium in London's Science Museum is to demonstrate the properties of its materials: glass and stainless steel. A transparent (or at least translucent) deck spans 16m and is composed of over 800 glass planks (laminated together in groups of five) 1mm thick and set on edge to form a 100mm deep continuous bearing surface divided into trays by surprisingly thin stainless steel sections. Most of the vertical loads are taken by thin stainless steel wires that fan in a shimmering cat's cradle from the tops of the columns of the old building to support the metal frames of the glass deck. The magical glass plane is held laterally by guys of stainless steel rope tying the structure to the base of the old columns. The stays are attached to the junctions of the trays from which steel balusters rise to support plain glass sheets.

The museum proudly announces that the selfweight of the bridge is 8.5 tonnes, that it can carry 12 tonnes, and that all this is held up by 2.6km of wire, 1.58mm in diameter, which weighs a mere 40 kilos. But these statistics give no idea of the presence of the object. The thick, green-tinted glass (optical glass would have been far too costly) is not perfectly transparent, though you can see through it, both from below, and as you walk across. Looking down, the slightly blurred image of the brightly-lit information desk reminds with a frisson that you are standing on glass, 10m above ground. Looking up from below, there is a dramatic demonstration of refraction: the feet and legs of people seen through the deck seem to be cut off and walking in advance of their heads and bodies seen through the balustrades - an appropriate visual phenomenon in a gallery devoted to the properties of materials.

The bridge also has aural properties. The stress gauges that connect the steel arcs to which the wires are anchored to the steel structure of the old building are wired up to a computer, which converts their output to generate noises that vary from a dull boom if you stamp on the bridge to a long angry throaty roar if you pluck one of the wires firmly. There are other sounds too - sibilations of different intensities if the glass plane is loaded at all, an occasional bell - and sometimes the bridge speaks, in a distant, mysterious, half-audible male voice '...On wires...Glass...Stainless...' Lights over each end flash in some kind of unison with the sounds. Clearly, the huge device is waiting for Philip Glass to create the first bridge concerto - it will be played by an ordered gymnastic troupe of children, who will surely enjoy the strange properties of the structure as much as those who now scamper across it undisciplined.