快猫短视频

WHILE on a camping trip in Netanya, Israel, Dora Jerby and her friends saw a football-sized orb emerge from near the seashore. 鈥淚t seemed to be emitting light from its core,鈥� she says. That was 50 years ago. Now, her son Eli Jerby has created a floating ball of flame in his lab, and thinks it might help explain the weird phenomenon of ball lightning.

Eyewitness accounts of ball lightning describe glowing spheres of various colours and sizes, ranging up to a few metres across. Some drift slowly high up in the sky, others zoom down low. Most bizarrely, ball lightning has been seen to pass through closed windows. In one famous sighting in March 1963, a glowing sphere floated down the aisle of an Eastern Airlines aircraft that had been struck by lightning.

In 2000, John Abrahamson and James Dinniss at the University of Canterbury in Christchurch, New Zealand, came up with a theory to try to explain some types of ball lightning. They suggested that when ordinary lightning strikes the ground, it converts mineral grains in the soil into silicon nanoparticles. These are ejected and form chains that burn in the air, creating the glowing ball. However, researchers have been unable to produce such fireballs in the lab.

Jerby might now have done so. In 2002, he developed a microwave drill at Tel Aviv University in Israel, which focused energy through a drill bit to create a hotspot on the surface of a material. 鈥淏ut there was an unwanted side effect,鈥� says Jerby. 鈥淲hen we pulled the drill out of the material it would drag out a molten blob, which sometimes burst into a fireball.鈥� The fireballs floated and quivered like jellyfish, he says.

At the time Jerby found a way to prevent these unwanted fiery orbs (快猫短视频, 26 October 2002, p 21), but he remained fascinated by the phenomenon. He and his colleague Vladmir Dikhtyar tried to produce fireballs by drilling into a layer of silicate in a microwave chamber. In each case the drill created a molten hotspot that burst into a column of flame. The column then formed a ball, which floated up to the chamber鈥檚 ceiling (Physical Review Letters, vol 96, p 045002).

At just a few centimetres across, Jerby鈥檚 fireballs are smaller than natural ball lightning, and they only last for about 40 milliseconds once the microwave source is switched off. But Jerby thinks his experiment supports Abrahamson and Dinniss鈥檚 theory, with the microwave drill playing the role of lightning.

The biggest test for any artificial ball lightning is whether it can pass through glass. Jerby did try that. 鈥淲e broke the glass,鈥� he says. The fireball cracked the glass, etching an outline of its shape on the sheet. Intriguingly though, some eyewitnesses have described ball lightning melting glass and breaking through it in this way.

Graham Hubler, a ball-lightning specialist at the US Naval Research Laboratory in Washington DC, believes Jerby鈥檚 work has interesting similarities with Abrahamson and Dinniss鈥檚 theory, but thinks that it can鈥檛 be the whole story. 鈥淭here are too many accounts of ball lightning passing through closed windows to ignore, and Abrahamson and Dinniss鈥檚 theory can鈥檛 account for that at all,鈥� says Hubler.

He says there is still room for theories based on electromagnetic mechanisms, which could allow ball lightning to move through glass. One such alternative is the recently proposed laser-ball theory (see 鈥淟ightning laser show鈥�). 鈥淚t may be that different types of ball lightning are caused by different processes,鈥� says Hubler. 鈥淏all lightning has always been an enigma, and it will remain one for a long time.鈥�