Dowsing: is it all done with magnetism?

Evidence continues to accumulate that there is a wide range of organisms with magnetic sensors. Could such a sense be the origin of the dowsing capability that so many people have claimed down through the ages?

This intriguing possibility has been raised by David Presti and John D. Pettigrew of the California Institute of Technology in reporting some of the latest research on the magnetic receptors of migratory birds. It could provide a scientifically credible explanation for what has often seemed no more than folklore.

Over the past decade, a number of investigations have shown convincingly that homing pigeons, especially, can use Earth's magnetic field for guidance. Moreover, in recent years, deposits of magnetite -- the historic lodestone -- have been found in organisms as diverse as bacteria, honeybees, and birds.Indeed , Presti and Pettigrew make their comment about dowsing in a paper in Nature that is primarily a report of what appear to be magnetite deposits in the necks of homing pigeons plus indications of magnetic sensors in a variety of migratory birds.

The magnetic sense had been something of a mystery for it was hard to see how biological tissue could detect the subtle changes in Earth's weak magnetic field which pigeons, for example, seem able to sense. There is some evidence to suggest that pigeons can use small systematic north-south changes in the strength and orientation of Earth's field to help maintain a crude internal map of their environment -- not just to orient themselves as with a compass.

Many forms of biological tissue are electrical conductors, and electric currents are induced in conductors when these move across a magnetic field. However, it was hard to see how this effect could become the basis for a sensitive biological magnetic detector. Now it is clear that there is a widespread capacity to lay down easily magnetized material in biological tissue.

This may be a crucial discovery. Most materials do not respond strongly to Earth's magnetic field. But take a substance such as iron as magnetite that is readily magnetized by a weak magnetic field (the ferromagnetic effect) and you can build a compass. Couple such material to muscle tissue, which is especially sensitive to pressure and stretching, and you could have a sensor able to pick up Earth's magnetic field and detect subtle changes in it, Presti and Pettigrew suggest.

"It has not escaped our notice," they say, "that our proposed mechanism may be relevant to the claim that positive dowsing responses in humans . . . are correlated with relatively small changes in the local magnetic field [due, perhaps, to underground water]. As the dowsing instruments are held in such a way that the slightest movement of the wrists or forearms will be amplified . . . a magnetically sensitive muscle receptor could conceivably give rise to muscular movement sufficient to produce the classic dowsing responses."

There may be something in all that folklore after all.

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