Remember fulgurites? Of course you do, since Weather Eye yesterday was all about them. Occasionally, you may recall, when lighting strikes a sandy soil it forges a path several feet into the ground and fuses the surrounding material into a kind of glass. The end result is a narrow, deep and slender hole, perhaps half an inch in diameter and surrounded by a tube of glass - a fulgurite.
Now, a recent theory has it that fulgurites may play a part in the formation of one of the mysteries of the natural word, the rare phenomenon of ball lightning.
A "fireball", as these apparitions are sometimes called, has a typical brightness of a 100-watt light bulb, and can range in size from beans to basketballs.
It often drifts along some feet above the ground, as if wafted in a current of moving air, and then after several seconds disappears as quickly as it came.
Scientists are nonplussed about its origins. The vast majority occur in thundery conditions, when ordinary lightning has been observed as well, so it has been suggested that it may be some form of "brush discharge" of static electricity in the atmosphere.
Alternatively, perhaps it may be a vortex of air containing a dense concentration of inexplicably luminous gases.
A recent theory proposed by a New Zealand scientist, Dr John Abrahamson, recalls that the element silicon, a common constituent of many soils, has the unusual property of being unstable and oxidising at high temperatures. It reacts with the oxygen in the atmosphere and releases chemical energy in the form of light and heat.
His theory was that when a bolt of lightning strikes the ground, the intense heat vapourises silicon.
As the vapour drifts upwards and cools in the atmosphere, it condenses into tiny particles which, having received an electrical charge from the lightning, are attracted to each other and congregate together in a little cloud. Oxidisation then provides the fireball's glow.
This theory had a flaw, however. Experience and experiment confirm that the violence of a bolt of lightning would scatter any silicon vapour to the four winds, rather than provide a suitable environment for a neat little cloud of it to form.
And then Dr Abrahamson thought of fulgurites. His suggestion is that the cavity inside a fulgurite tube could provide very suitable shelter for the hot silicon vapour until the shockwave caused by the lightning strike has dissipated.
Then, he suggests, thermal expansion causes a little puff of the vapour to be expelled into the atmosphere. It cools, condenses, oxidises and - voila, ball lightning.