Tonight is Twelfth Night, the eve of Old Christmas Day, or Nollaig na mBan as it was called in Ireland. The convoluted contents of Shakespeare's Twelfth Night have nothing to do with the festival itself, except insofar as the Bard, allegedly at a loss for a title for his work, named it after the revelries of which its first performance was to form a part - probably those of January, 1601.
In the play, Feste the clown is allowed to do the honours in the closing scene, and sings a little verse that goes like this: When that I was a little tiny boy, With hey, ho, the wind and the rain, A foolish thing was but a toy, For the rain it raineth every day.
There are toys available which have relevance to the weather.
These devices, which can be seen on display in many households, are said to warn of the approach of rain. No one takes them very seriously - but they are fun to watch.
Most "weather toys" depend for their effectiveness on the reaction of certain substances to changes in humidity. This in turn assumes that a rise in relative humidity is a portent of rain - an assumption which is often justified, but by no means infallible.
Conversely, low relative humidity is taken as a sign of good weather - another criterion which is reasonable, but undependable. The relationship between humidity and approaching rain is tenuous - but it does exist.
Visual indications of a change in humidity can be provided in a number of ways. Some chemicals, for instance, change colour when they are damp; one such chemical is cobalt chloride, and a piece of paper impregnated with the substance will appear blue when the humidity is low, and pink or red when the air is damp - hence those little ornaments incorporating a street lamp and helpful advice along the lines: "Blue light, weather right; pink light, rain in sight."
Other devices depend upon the fact that some materials change shape with variations in humidity. Human hair is a case in point; it shrinks when damp. And an ordinary rope also becomes shorter when it is wet. A strand of such moisture-sensitive material, if fixed at one end and wound in a spiral, will rotate at the free end as the humidity goes up and down.
This phenomenon is used to operate the traditional Dutch Weather House - the little chalet where the man comes out if it is about to rain, and the woman emerges when dry weather is expected.