Sometimes, when the weather is particularly dismal, it seems as if Shakespeare may have had it right:
The winds have sucked up contagion from the sea
Contagious fog, which falling on the land
Has every pelting river made so proud,
That they have overborne their continent.
And in a sense his reasoning was plausible. The atmosphere acquires the moisture it needs for rain by evaporation from the sea and other water surfaces. Indeed it is the transformation of water from one "phase" to another, from the solid to the liquid to the gaseous state and back again, which accounts for nearly all the weather phenomena we experience.
Without this atmospheric volatility we would have no clouds or rain, temperature ranges would be much more extreme, and in general meteorology would be much less interesting.
We are very familiar with two of the phases of water, liquid water and ice. The third, however, can often be overlooked because of its colourless and transparent nature. As it happens there is only a tiny amount of water vapour in our atmosphere, about 4 per cent, but a very large part of the science of meteorology is concerned with precisely what happens to it. With three phases, six transformations are possible, and each of these occurs in nature.
The familiar change from solid to liquid is called melting, and that from liquid to solid freezing. Equally well known are evaporation, which is liquid transforming into water vapour, and its reverse process, a change from vapour to liquid, which is condensation. But the two remaining transformations are less obvious.
In both cases nature skips a step, and the process is known as sublimation. If the temperature is low enough, dry air trying to absorb water vapour will sometimes snatch it directly from a surface of ice; the ice, in a sense, disappears directly into thin air. And in the opposite direction at very low temperatures, water vapour "condenses" directly into ice.
This change from the vapour to the solid state is the process by which the tiny ice crystals of very cold clouds are formed. And in a more familiar setting it accounts for hoar frost, the white crystalline deposit seen on cold and frosty mornings.
Viewed like this, the seemingly incessant rain can at least be seen as part of a complex, interesting and never-ending process. It is possible even to be infected by the guarded optimism shown by Rupert Brooke:
One may not doubt that, somehow good
Shall come of water and of mud;
And, sure, the reverend eyemust see
A purpose in liquidity.