The Cloudspotter’s Guide, by Gavin Pretor-Pinney


The Cloudspotter’s Guide: The Science, History, and Culture of Clouds, by Gavin Pretor-Pinney. New York: Perigree, 2007. 320 pp. $16 (paperback).

Gavin Pretor-Pinney has loved looking at clouds since he was a child, and he shares what he loves about them in The Cloudspotter’s Guide: The Science, History, and Culture of Clouds. And, if you read this book, chances are good that you too will come to love looking at these wonders in the sky.

As the subtitle suggests, The Cloudspotter’s Guide is a collection of facts about clouds and how people view them rather than a strictly scientific account of what they are and how they are formed. This, for example, is how Pretor-Pinney introduces the cumulus cloud:

Leonardo da Vinci once described clouds as “bodies without surface,” and you can see what he meant. They are ghostlike, ephemeral, nebulous: you can see their shapes, yet it’s hard to say where their forms begin and end.

But the Cumulus cloud is one that challenges da Vinci’s description. Rising in brilliant-white cauliflower mounds, it looks more solid and crisply defined than other cloud types. As a child I was convinced that men with long ladders harvested cotton wool from these clouds. They look as if you could just reach up and touch them—and, if you did, they would feel like the softest things imaginable. . . .

Cumulus is the Latin word for “heap,” which is simply to say that these clouds have a clumpy, stacked shape. The people who concern themselves with such things divide them into humilis, mediocris, and congestus formations—these are known as “species” of Cumulus. Humilis, meaning humble in Latin, are the smallest, being wider than they are tall; mediocris are as tall as they are wide, and congestus are taller still. (p. 21)

Following this, Pretor-Pinney notes the typical altitude of cumulus clouds, shows pictures of the different varieties, and discusses ways to distinguish them from other clouds that may look similar, how and where they form, and interesting facts or stories about them. He does the same for each kind of cloud he examines.

Pretor-Pinney condenses some of this data into boxes at the beginning of each chapter, which is useful for reference, but for the most part he relays the information in prose that flows from one mystery and its answer to another. Consider the first big mystery of a cumulus cloud—the question of what exactly it is:

It may feel rather unsatisfying to hear that it is just water. And yet, like all clouds, that is all it is. The curious cloudspotter might therefore wonder why it looks so different from a glass of stuff down here on the ground. The cloud’s white appearance is because the water is in the form of countless, tiny droplets (well, around 350,000,000,000 cubic feet in actual fact), each only a few thousandths of a millimeter across. And this array of innumerable tiny surface scatters the light in all directions, giving the cloud its diffuse, milky appearance as compared with the single surface of a container of water. . . .

It is somewhat alarming to learn that eight elephants weigh about as much as the water droplets in a medium-sized Cumulus—a Cumulus mediocris—would if you added them all together. For, though the droplets in a Cumulus cloud are extremely small, there are one hell of a lot of them. Given that elephants don’t tend to fly these days, how exactly does the water equivalent of eighty of them rise to form a cumulus?

There’s a clue in the cloud’s tendency to appear on a sunny day. For when the sun is shining, currents of air known as thermals, or convection currents, start to form as it warms the ground. These rising plumes of air are the light turbulence you feel as you pass through Cumulus in an aeroplane. They are the reason why hang gliders and eagles will head toward this type of cloud, knowing that it is a celestial signpost for the updraughts that give them lift. Thermals are the invisible spirits that give lift to the Cumulus. They bring it into being, flowing through it, animating it. To understand the formation of thermal convection currents is to glimpse the soul of a Cumulus cloud. They are what get the moisture up there in the first place and also what help the cloud’s droplets to stay airborne. (pp. 26–28)

Of course, this explanation of what a cumulus cloud is raises a host of additional questions—such as what it means for the air in a thermal to “contain” moisture and how it changes into the visible droplets we see as a cloud. And Pretor-Pinney proceeds to answer these questions, along with similar questions arising from his descriptions of different clouds. In doing so, he discusses various experiments with clouds, the appearance of clouds in artwork, and our experiences with them. For instance, in one experience that shed light on the nature of the cumulonimbus thundercloud, Pretor-Pinney tells of a pilot’s harrowing experience in which his plane malfunctioned while he was attempting to fly over one of these massive towers in the sky, and, after ejecting, he fell through the cloud and amazingly lived to explain what it was like.

The Cloudspotter’s Guide thus has much to offer anyone interested in these islands of water in the air. Pretor-Pinney does not delve deeply into the science of these marvels, and I for one wish he had shared more about how scientists discovered what they know about clouds. But the explanations he provides are fascinating and may inspire curious readers to look further into the matter on their own.

Unfortunately, some of the “science” Pinney does include is not science at all, but, rather, environmentalist dogma. This is the one significant problem with the book. Pretor-Pinney’s acceptance of environmentalist bromides causes him to pass along junk science about global warming as well as monstrous proposals for solving the alleged problem. For example, in his chapter on contrails—the clouds that form in the wake of an airplane—Pretor-Pinney suggests that they may be “the writing on the sky,” telling us that we’re destroying the environment, and calling for us to drastically change our behavior (pp. 280, 276). The environmentally religious will see nothing wrong with such comments, but they are unbecoming of a man of science, and they don’t belong in an otherwise pleasant and lighthearted book.

Fortunately, such forays into nonsense are rare in The Cloudspotter’s Guide—so rare that they should not stop anyone from reading the book. For most of the book, Pretor-Pinney displays the proper approach to nature and man’s relationship to it: He studies it with enthusiastic curiosity, appreciates how appealing it can be, and looks for ways to use what he understands to better enjoy life—whether taking a deep breath of fresh air after clouds have cleansed it with rain, or soaring through clouds in a glider plane just for the fun of it.


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