PORTLAND, Ore. Ball lightning has mystified electricity researchers since Benjamin Franklin first flew his kite in 1752. The very next year, Russian scientist Georg Richmann was killed by ball lightning while flying a kite modeled on Franklin's experiment.
Since then, dozens of hypotheses have been offered to explain ball lightning, from Nikola Tesla's seminal 1904 treatise, "The Transmission of Electrical Energy Without Wires," to the most recent explanation offered by University of Canterbury (Christchurch, New Zealand) professors John Abrahamson and James Dinniss, that ball lightning is just vaporized silicon.
Now researchers Antnio Pavo and Gerson Paiva of the Federal University of Pernambuco in Brazil claim to have verified the vaporized silicon hypothesis in their laboratory.
"Several years ago, I predicted that the University of Canterbury hypothesis could be tested in the lab, and now these Brazilian experimenters claim to have done it," said Graham Hubler, a physicist at the U.S. Naval Research Laboratory in Washington. "Heck, there will probably be kids making ball lightning in their science lab classes."
Here's the theory: Sand, or silicon dioxide (also called silica) can be vaporized by a lightning strike in the presence of carbon, causing the short-lived, glowing, floating objects called ball lightning. The theory maintains that the silicon vapor glows from the heat produced when it recombines with oxygen in the air. That, according to the hypothesis, maintains the ball shape due to condensing silicon on its outside surface that is bound by the electric charge of the lightning.
To test the hypothesis, Pavo and Paiva subjected a silicon substrate to a high-voltage arc with 140 amps of current. As they moved the electrodes apart, an arc vaporized the 350-micron-thick substrate, creating luminous orbs the size of a golf ball.
"In the soil, you have to also have carbon present to make this theory work, because the oxygen in silicon dioxide likes the carbon. So when the lightning vaporizes the silica, its oxygen bonds with the carbon, leaving pure silicon in the hot vapor that forms the lightning balls," said Hubler. "The Brazilian researchers just simplified their experimental setup by starting with pure silicon."
According to Pavo and Paiva, ball lightning persisted for as long as eight seconds and emitted jet plumes and smoke trailsboth described in anecdotal accounts of ball lightning. Ball trails spiraled away, suggesting that lightning balls rotate. Color varied from blue to orange white; temperature was estimated to be around 2,000 degrees Kelvin (3,140 degrees F).
The researchers next plan to investigate whether other soil components such as metal alloys and various sulphur compounds could also be vaporized into balls when struck by lightning.