Arthur C. Clarke once famously pronounced that any sufficiently advanced technology is indistinguishable from magic. The reverse, of course, is not so true. Just because something seems to need magic to explain it does not make it an advanced technology: a more conventional explanation, such as sleight of hand, is usually involved.

Even so, some apparently magical ideas survive even when there is no decent scientific explanation for them. One is that applying a magnetic field to a water pipe can soften the water flowing through it and so prevent the pipe from scaling up. Devices based on this idea crop up regularly in the classified advertisements, alongside improved potato-peelers and better mousetraps. Domestic versions cost around $300; industrial ones up to $30,000. Physicists, unable to explain how such machines could work, have dismissed them for years. Physicists, it appears, are wrong.

The evidence comes from Simon Parsons and his team at Cranfield University in Britain. They put the tale to the test and found that it is not as tall as it seems. Indeed, given the right combination of magnetism, temperature, acidity and water flow, they found that the rate of scaling could be halved. This is potentially impressive. Dr. Parsons reckons that scaling costs British industry $1.5 billion a year. Halving that cost would be a useful gain. What is not clear is just how the process works. On March 14th a seminar at Cranfield, which will be addressed by physicists from America and Japan, as well as Europe, will explore the problem.

One clue they will have to go on is that the limited amounts of scale produced in Dr. Parson's experiments do not form a solid crust that requires major surgery to remove, but rather a powdery layer that can be eliminated with a stiff brushing. Examined under an electron microscope, the crystals that make up this layer look circular. Those in common or garden limescale are rectangular. It seems that the magnetic field changes the way in which the calcium carbonate that makes up scale crystallizes.

Dr. Parson sees four possible explanations. The most esoteric is that the magnetic field is changing the shape of the orbitals occupied by the electrons surrounding the atoms involved. This would certainly change their chemical reactivity. But he thinks it is extremely unlikely that his magnets could have this effect.

Another possibility is that the field is causing impurities in the water, such as iron atoms, to stick together in ways that form nucleation sites: places around which calcium carbonate can easily crystallize. By forming in the flowing water, rather than accumulating on the edge of the pipe, the crystals would not fur things up.

The third idea is that the magnetism changes the way that calcium ions attract water molecules. When ions (electrically charged atoms) dissolve in water, their charges cause nearby water molecules to cluster around them. This, of course, interferes with their ability to react with other ions. If you make changes in the nature of its protective shell, you change an ion's reactivity.

The fourth theory is that the field distorts the electrical charge that is carried by small particles of calcium carbonate that have already formed in the water. This, in turn, affects the way they stick together to form large particles.

For Dr. Parson's money, the fourth explanation is the most likely. It is the only one that fits with the observation that the magnets work only on flowing water. Whereas electrically charged objects sitting still in a magnetic field do nothing, those moving through a field generate a further electrical charge, which will also change their attractiveness to each other.

Dr. Parson's money, though, is not the only interested cash. The oil industry, in particular, is watching the work done at Cranfield. Oil wells face major scaling problems from the highly mineralized waters extracted along with the pay dirt. Chemical treatment costs as much as $750,000 a year for a typical North Sea platform, and some magnetic devices are already being tested; an industry that is often based on hunches is certainly willing to give them a try. But without a theoretical explanation for the magic boxes, which would give some idea of their limitations, hard-headed engineers are reluctant to invest in them more widely. Perhaps, if Dr. Parsons and his collaborators can manage to explain this particular magic, a new technology will be born.

(Note: Dollar amounts have been changed from British Pounds to US Dollars)