THAT well known raconteur of the early 19th century, the Rev Sidney Smith, was once heard to remark, rather unkindly, that "I have, alas, only one illusion left, and that: is the Archbishop of Canterbury". Meteorologists are in a somewhat similar position; they have succeeded, by and large, in finding explanations for all known atmospheric phenomena save one. They still see no rhyme or reason to ball lightning, indeed some professionals are sceptical that it exists at all.
Although a very rare occurrence, ball lightning has now been seen so often by reliable witnesses that very few, in fact, now dismiss it as hoax or mere imagination. The "fireballs" as they are sometimes called, may be white, red or, orange in colour, and range in size from beans to basketballs. The apparition is often accompanied by a hissing sound and a distinctive smell; it typically drifts along some feet above the ground, as it wafted in a current of moving air, and then, after several seconds it disappears as quickly as it came.
Now that I come to think of it, my opening Episcopal allusion was an apt one, since one of the earliest records of this phenomenon was in the 4th century when a ball of fire appeared over the head of Bishop Martin of Tours as he was saying Mass, and then rose heavenwards. This singular event must have provided persuasive evidence to be used by Martin's advoeatus dei, when his suitability for sainthood came to be debated some years later.
The strange fireball seems to be relatively harmless - "lambent but innocuous", as yet another cleric once described the scintillations of a colleague's wit. People who have come into contact with it have suffered no ill effects other than slight shock. The vast majority of occurrences take place in thundery conditions, when ordinary lightning has also been observed.
The relationship between this phenomenon and common lightning, however, is to say the least uncertain, as indeed is the truth of any of the explanations for its cause. It has been suggested that it may be some form of "brush discharges" of static electricity in the atmosphere, or a vortex of air containing a dense concentration of inexplicably luminous gases. And some refuse to believe that it exists at all, asserting that it is merely an optical illusion, caused by an afterimage on the retina of the eye immediately following a lightning flash seen by the observer; they place it in the same category as Hamlet senior's ghost: "Horatio says tis but our fantasy, and will not let belief take hold of him."