"Blue skies, smiling at me," goes the Irving Berlin song, "Nothing but blue skies do I see." Berlin thought that was a good thing, but Gavin Pretor-Pinney would not. For him, clouds are there to be enjoyed, and they make that blue more beautiful by its being in the background. He does not feel there is anything depressing about having "a cloud on the horizon" and he sees no reason that we should link clouds with catastrophe, as in "clouds of doom", or with ill-will as in "clouds of suspicion". He feels clouds are underappreciated, and so a couple of years ago, he founded the Cloud Appreciation Society, complete with badges. As he says, "Of course, an organization only exists when it has a website," and indeed the CAS has one, full of photographs and poems by members, a picture of the Cloud of the Month, and chat rooms, with this stated purpose: "If you've got something to tell us, we'd love to hear it. But only if it is about clouds. Otherwise we're not interested." Pretor-Pinney would like us all to be cloudspotters, and has produced _The Cloudspotter's Guide: The Science, History, and Culture of Clouds_ (Perigee), a witty and informative volume for those who want to take an educated view of his favorite subject. He emphatically agrees with John Constable, who could paint clouds like no one else: "We see nothing truly until we understand it." The book cannot fail in its mission of increasing both understanding and seeing.
We start understanding things when we can categorize them, and over the years, observers learned there were differences in cloud types and they attached names to them. The first person to take on this task did not do so until the nineteenth century. Luke Howard, an English Quaker, in 1802 lectured his local scientific society on cloud types, and as was the Linnean fashion, sorted them into genera and species and gave them Latin names, like Cumulus and Stratus. It was a good system, but different nations and regions started adding their own cloud types and cloud names. The confusion was cleared up in 1896, the "International Year of the Clouds". Serious meteorologists formed a "Cloud Committee" and published _The International Cloud Atlas_, sorting clouds into ten genera accompanied by descriptions and photographs. Each of the ten clouds has a chapter in Pretor-Pinney's book, complete with description and lore, and photographs by members of the CAS, along with their membership numbers. For example, chapter one is on the Cumulus cloud, the low, puffy, detached clouds, the sort that children draw in their pictures: "Six year olds are generally rubbish at drawing, but being amongst the best cloudspotters in the world, they are actually quite good at drawing Cumulus." To explain the formation of the Cumulus, the author cheerfully describes the process as compared to a lava lamp, and in the meantime explains lava lamp physics as well. We think of clouds as filmy and light, but a typical Cumulus will have around 220 tons of water droplets in it. Certainly, though, not all is seriousness here. Seeing shapes in clouds is not just a child's game, and the author recommends it: "Clouds are for dreamers, and the contemplation of their shapes is a pursuit worthy of any cloudspotter... any cloudspotter who has become too sensible to see shapes in the clouds needs to re-evaluate."
Pretor-Penney has a great deal of fun with his hobby, fun that comes through in every chapter of his book. For example, in investigating the mackerel sky (a type of Cirrocumulus), he goes to the biggest fish market in London to see which fish had lent its pattern of scales to the name. He finds the mackerel sky within the scales of the king mackerel, but stops in his tracks when he realizes that the scales of the common carp reproduce Altocumulus stratiformis perlucidus, "soon to be known as a 'carp sky'". Few other people could have traveled across the world to see a particular cloud, but you can read his report on the Morning Glory, a type of Stratocumulus that forms in northern Australia in the spring, a huge roll of a cloud that can be six hundred miles long. It is favored by glider pilots who use it as surfers do an ocean wave. There are many other interesting asides here, caught with enthusiasm and humor, within the meteorological rigor. Many readers will want to keep their copy handy as it has "How to Spot..." guides for all the clouds, and how not to confuse them with others. This is one of the most entertaining reference books ever.