Transcranial magnetic stimulation is an extraordinary technique pioneered by neuroscientists to explore the workings of the brain. The idea is to place a human in a rapidly changing magnetic field that is powerful enough to induce currents in neurons in the brain. Then sit back and see what happens. [...] Focus the field in the visual cortex, for example, and the induced eddys cause the subject to 'see' lights that appear as discs and lines. Move the the field within the cortex and the subject sees the lights move too.

But if this happens in the lab, then why not in the real world too, say Joseph Peer and Alexander Kendl at the University of Innsbruck in Austria. They calculate that the rapidly changing fields associated with repeated lightning strikes are powerful enough to cause a similar phenomenon in humans within 200 metres. [...] It turns out, of course, that there are numerous reports of these types of observations during thunder storms. "An observer reporting this experience is likely to classify the event under the preconcepted term of 'ball lightning'," say Kendl and Peer.

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