For hundreds of years eyewitnesses have reported brief encounters with the golf ball- to tennis ball-size orbs of electricity. But scientists have been unable to agree on how and why ball lightning forms, since the phenomenon is rare and very short-lived. (See "Ball Lightning: A Shocking Scientific Mystery.")

Ball lightning is often reported during thunderstorms, and it's known that multiple consecutive lightning strikes can create strong magnetic fields. So Joseph Peer and Alexander Kendl at the University of Innsbruck in Austria wondered whether ball lightning is really a hallucination induced by magnetic stimulation of the brain's visual cortex or the eye's retina.

In previous experiments, other scientists had exposed