Now what should one do when it is raining cats and dogs? Run helter-skelter to the nearest shelter, thereby suffering a soaking down the front? Or should one take one's time, encountering fewer raindrops in any given interval, but enduring the unpleasantness for rather longer? Which option leaves an individual least wet? Or for that matter, to ponder another side of this important question at a deeper level, why do we talk of heavy rain in terms of "cats and dogs"?
The answer to the latter question is lost in the mists of time. One implausible explanation recalls the ancient belief that witches, for reasons best known to themselves, used to ride along in storm-clouds cleverly disguised as cats. Moreover, in Norse mythology, the dog, like the wolf, was an attendant of the chief god, Odin, who was responsible for gales and storms. The theory is, therefore, that cats and dogs in some way symbolise the combined efforts of Odin and the witches, representing a downpouring of rain and vicious blasts of wind respectively.
But we have a precise answer to the first dilemma - how to minimise a soaking in a heavy shower. Some time ago, meteorologists from Reading University researched the problem in considerable detail, using calculus.
They assumed, for the purpose of their argument, that the rain was falling vertically, and that its intensity was constant over time. A person standing still when exposed to such a downpour will have the rain falling directly on his horizontal surfaces; if, on the other hand, he moves, he will also collide with any raindrops in his way.
Obviously, if the subject of this experiment just stands still, he will get very wet indeed because the rain will fall on him indefinitely. But if he moves, the total amount of water encountered turns out to decrease rapidly as he increases his rate of progress to a brisk walk - for the simple reason that the faster he travels, the quicker he reaches shelter. But surprisingly perhaps, beyond a brisk walk, any further increase in speed has very little effect upon how wet he gets: if he runs like mad, he will reach the shelter very quickly, but at this higher speed he will have collected more raindrops on the way, and consequently experienced a more serious wetting down the front.
The best tactic, it seems, is to head for the nearest shelter at precisely six miles per hour, or slightly more than walking pace. If you move more slowly, you will catch more rain - and to go any faster is simply just not worth the extra energy required.