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# Short takes on six books

BIRDING BABYLON: A Soldier's Journal from Iraq. Jonathan Trouern-Trend. Sierra Club Books, \$9.95.

While deployed in Iraq, Sgt. 1st Class Jonathan Trouern-Trend began a Web log to record and share his bird sightings. On walks around Camp Anaconda, a large base north of Baghdad, and on occasional forays into other parts of the country, Trouern-Trend spotted more than 100 species, a number of which were new additions to his "life list." At first he was surprised by the attention his blog received, but he thinks he knows now why people so appreciated his brief dispatches: "To read about something as universally familiar as the migration of birds, or watching ducks in a pond, fulfilled a need to know that something worthwhile or even magical was happening, even in the midst of suicide bombings and rocket attacks." Birding Babylon, a small but compelling book, is a compilation of some of the entries recorded over the course of his year-long tour of duty. The blog, which Trouern-Trend continues to update, can be read at http://birdingbabylon.blogspot.com—Amos Esty

Negative Math:How Mathematical Rules Can Be Positively Bent. Alberto A. Martínez. Princeton University Press, \$24.95.

Children seldom have much trouble with 2 + 2 = 4 or 2 x 2 = 4, but -2 x -2 = 4 is another matter. Why should two negatives make a positive? Whatever explanation you might suggest, why doesn't it also apply to -2 + -2 = -4? Generations of students have stumbled over this issue. One of them was Henri Beyle, who recalled of his school days in the 1790s: "When I spoke of my difficulty about minus times minus to one of the experts, he laughed in my face." Perhaps if Beyle's teachers had been more sympathetic and less dogmatic, he would have gone on to a career in mathematics instead of writing novels under the pen name Stendhal.

Beyle gets plenty of sympathy from Alberto A. Martínez, who shows that the concept of negative numbers has perplexed not just young students but also quite a few notable mathematicians, such as Sadi Carnot and Augustus de Morgan. And with good reason: The rule that minus times minus makes plus is not in fact grounded in some deep and immutable law of nature. Martínez shows that it's possible to construct a fully consistent system of arithmetic in which minus times minus makes minus. It's a wonderful vindication for the obstinate smart-aleck kid in the back of the class.—Brian Hayes

SKY IN A BOTTLE. Peter Pesic. MIT Press, \$24.95.

Why is the sky blue? That may be the single most common question about the natural world—and one of the most beguiling. The 13th-century scholar Roger Bacon believed the sky took its color from a "heaven of water" beyond it; Swiss mathematician Leonhard Euler thought air contained "a great quantity of small blue particles." As recently as 1862, Sir John Herschel listed the color and polarization of sky light as "the two great standing enigmas of meteorology."

That's because the answer is surprisingly complex, involving chemistry, optics, atomic physics and cosmology. The conventional explanation is that the rarefied upper atmosphere scatters sunlight's shorter wavelengths. But if not for a quirk of human vision, our sky would appear violet, and if our atmosphere were denser it might look orange or red. The saying "as sure as the sky is blue" overlooks a wealth of fascinating subtleties.

Physicist and historian Peter Pesic lucidly explores those subtleties in Sky in a Bottle, which takes its title from experiments like that conducted in 1871 by physicist John Tyndall, who briefly produced a color he compared to "the deepest and purest Italian sky" by shining an electric lamp through vapors at low pressure (see apparatus above). Pesic's book becomes a pocket history of science, with thinkers from Aristotle to Einstein contributing new ideas, conjectures and discoveries to explain that serene, impassive blue.

Their efforts have been well rewarded. Ultimately, investigation of the sky's color helped establish the physical reality of atoms, and our modern understanding involves even quantum theory. "For myself," Pesic writes, "I find it strange and beautiful that such simple questions lead to such deep realizations about the nature of the universe."—Greg Ross

THE REAL MARS: Spirit, Opportunity, Mars Express and the Quest to Explore the Red Planet. Michael Hanlon. Carroll and Graf Publishers, \$35.

The Real Mars introduces readers to facts, theories and fantasies about the fourth planet from the Sun, which has fascinated us since ancient times. The first half of the book focuses on the late 19th and 20th centuries. Without getting bogged down in detail, Hanlon discusses the main debates, explaining how some controversies have been resolved by technological advances and how others have emerged. The text is liberally sprinkled with images of the planet and its surface taken by Viking, Pathfinder and most recently the twin rovers Spirit and Opportunity.

There are a few curious omissions. In the section where works of Mars-related fiction are discussed, the excellent trilogy by Kim Stanley Robinson (Red Mars, Green Mars, Blue Mars), which offers a seminal account of how the planet might actually be colonized and terra-formed, is not mentioned. The book's longest chapter covers recent successful voyages to Mars, devoting the most space to Spirit and Opportunity, arguably NASA's most successful planetary mission to date. Yet there is not one picture of the rovers themselves. However, these flaws are minor. This is a well-written introduction for nonexperts, sure to inspire further interest and study.

Shown above is a photo of Pathfinder's cushioned airbag landing system.—Roger Harris

FAB: The Coming Revolution on Your Desktop—From Personal Computers to Personal Fabrication. Neil Gershenfeld. Basic Books, \$26.

In FAB: The Coming Revolution on Your Desktop—From Personal Computers to Personal Fabrication, MIT professor Neil  Gershenfeld points out that not so long ago, digital computers were huge, costly, room-sized contraptions to which only the techno-elite had access. Nowadays, of course, computers of far greater power are found in every college dorm room. Gershenfeld contends that a similar evolution will take place with the high-tech fabrication tools used in industry: computer-controlled milling machines and routers, laser cutters, water-jet cutters, even 3-D printers. Soon, Gershenfeld posits, such devices will start cropping up on home and office desktops, allowing regular folks to build customized goods for their own use rather than contenting themselves with what's available on store shelves. He gives dozens of examples, largely drawing from his experiences teaching a wildly popular MIT class titled "How to Make (Almost) Anything."

Gershenfeld relates many charming anecdotes and displays a lively sense of humor, but, sadly, the thesis he presents remains difficult to accept. Although the general premise—that computerized machine tools will become increasingly accessible—is not unreasonable, the notion that everyone will soon be making anything (or almost anything) they want seems just plain fanciful. Gershenfeld's description of his five-year-old twins as "shop users," ones able to design and build rather complicated toys (seen above) with a laser cutter, convinced me he was sorely overstating his case. Were such young kids able to master the rather challenging tasks involved, which I doubt, would parents welcome into their homes machines that could swiftly blind or maim their children? And even with inexpensive fabrication tools widely available, the economics of custom fabrication will never rival mass production. Hence I suspect that Wal-Mart has nothing to worry about. Rather, I imagine that the personal fabrication Gershenfeld champions will more resemble making one's own clothes: a creative and satisfying but not particularly cost-effective or popular endeavor.

Gershenfeld's credibility also suffers from some silly technical blunders. He erroneously refers to Avogadro's number as the number of molecules of an ideal gas that can fit in one cubic centimeter, and he mistakenly calls the machine language that a microprocessor runs "microcode," to give two examples. Still, there is plenty of food for thought in this book, which provides a rare view of the world of computer-controlled fabrication tools, devices that few people have ever seen. But be forewarned—the window Gershenfeld provides has a very rosy tint.—David Schneider

THE SINGING LIFE OF BIRDS: The Art and Science of Listening to Birdsong. Donald Kroodsma. Houghton Mifflin, \$28.

Some birds learn their songs from their neighbors, whereas others appear to have a genetic program that encodes the tune like the paper roll on a player piano. It's a deep puzzle why avian vocalizations are inherited in such very different ways. In The Singing Life of Birds, Donald Kroodsma, professor emeritus at the University of Massachusetts, Amherst, explores this and other avian musical mysteries by examining the songs of 30 different bird species. Each offers lessons on some fundamental questions about avian vocalizations. One of the more delightful songsters we learn about is the brown thrasher (Toxostoma rufum, shown at right), whose prolific repertoire may number in the thousands. How often does the brown thrasher repeat his songs? How does he remember all of them? Does he make some up as he goes along? Nobody (except the bird himself) knows the answers. And so it goes for many other songbirds who hold their melodic secrets close to the breast.

The book comes with a 98-track CD of birdsongs that correspond to sonograms (graphs that plot a sound's frequency over time) found in the text. Looking at a sonogram while listening to a song allows a listener to see components of a bird's vocalization that pass too quickly for the naive human ear to catch them. If you are struggling with learning the song of a bird, studying a sonogram can bring clarity to a string of sounds that seems too complicated to resolve and remember. In combination with Kroodsma's engaging explanations, the CD and sonograms offer a unique perspective on how our feathered friends communicate to the world through song.—Michael Szpir