A fresh breeze

IN the opening pages of “An Ocean of Air,” author Gabrielle Walker plunges the reader into the subject of her book -- literally. A test pilot hurls himself from the gondola of a helium balloon floating on the black edge of space. As he plummets, he passes through layers of atmosphere: the ionosphere, the stratosphere, the ozone layer, the troposphere. Walker keeps the tension high. Were a pin to prick his pressure suit in the first seconds of his fall, his blood would instantly boil, killing him.

After such a descent -- evocative of a submarine dive -- it’s easy to view the atmosphere as an ocean. Walker next explains how the gas blanket came to be viewed this way through centuries of history. Surprisingly, the great astronomer Galileo was wrong about air. He thought that liquid was pulled through a siphon because of suction created by a vacuum; in fact, it’s the weight of the air that pushes the liquid into a vacuum. Had he been able to talk about his ideas with colleagues, he might have revised them. But about the time the Roman Catholic Church censured Galileo for belief in heliocentrism, it also decreed that it was heresy to say a vacuum could exist.

Almost as destructive to science as the Church’s edicts were the alchemists, one of whom, Walker mentions, “published a recipe for making mice out of dirty underwear and wheat.” Amid this willful ignorance, the early breakthroughs that led to the truth about air seem that much more remarkable.

Walker also explores how air moves across the planet. Before Columbus planted Spain’s flag in the New World, he discovered the trade winds, benign gusts that blow from east to west. She notes archeologist Thor Heyerdahl’s theory that ancient mariners used trade winds to bring pyramids to Central America, then discredits it with this delicious bit of faint praise: “[I]f the ancient Egyptians did reach the Americas with tales of their pyramidal technologies, you’d think that they would also have mentioned the wheel.”

Just as Walker can easily shred theories with her sharp wit, she also advocates persuasively -- as she does for William Ferrel, a “farm-boy-genius” who figured out why storms circle in different directions in the Northern and Southern hemispheres. They react to Earth’s spin, a pattern variously called the “Coriolis effect,” after French mathematician Gustav Gaspard Coriolis, and “Buys Ballot’s Law,” after the Dutch scientist who noticed it. To rectify what Walker perceives as an injustice, she calls it the “Ferrel effect.”

Walker has a PhD in chemistry, but she writes like a poet. With a few deft strokes, she brings wacky characters to life. My favorite is Wiley Post, a one-eyed pilot and former highway robber who discovered the jet stream. But because he was an obnoxious attention-grabber, few people believed him.

The book’s last sections explore the fragility of the atmosphere -- and what global warming and a receding ozone layer mean to the planet’s inhabitants. In this way, “An Ocean of Air” sounds a warning, but not one that is shrill or grating. Walker’s book should absorb and delight anyone who breathes.