PUSHING THE LIMITS

New Adventures in Engineering

By Henry Petroski. Knopf. 288 pp. $25

Norman Mailer, a onetime engineering student himself, once remarked that "Physics was love, engineering was marriage." He was right. A physicist looking at a bridge sees gravity pulling relentlessly down while the atoms in the iron and concrete squeeze against each other to exert a countervailing force and keep the bridge standing. An engineer looking at the same bridge will see some of this, of course, but will see a lot of other things as well. He or she will see the economic factors that dictated the use of materials, the complex strategies that had to be worked out to keep the structure standing during construction, the endless permits and forms that had to be filled out before the first shovelful of dirt was turned over, the court cases brought by environmental groups, and all the other elements that had to be dealt with before the grand principles of the physicist could be realized in this particular structure.

Henry Petroski, a professor of civil engineering and history at Duke University, has made it his calling to help the rest of us see the world through the eyes of the engineer. He has been called, deservedly, the "poet laureate of engineering." Pushing the Limits is a collection of essays, first published in somewhat different form in the American Scientist, that amounts to a kind of intellectual travelogue in which he shares with us an engineer's-eye view of everything from obscure bridges to crazy (and as yet unbuilt) structures that have been proposed by engineers in the past.

Petroski is an engaging writer, clearly in love with his subject. I enjoyed this book immensely, so let me get a minor criticism off my chest. It wasn't until page 257 (in the author's acknowledgments) that I learned that I was reading a book of collected essays. An earlier statement would have saved me a lot of trouble trying to figure out what the connection between chapters was. Once I figured it out, I could take each chapter as a self-contained unit (as was originally intended) and enjoy the book for what it is.

The first half of the book is taken up with a discussion of bridges. These are some of the most dramatic built structures in the world, not least because they often occur in dramatic settings -- harbors, gorges and the like. Petroski begins with a historical survey stressing bridge design as a creative activity -- "The fresh piece of paper on the drawing board is as blank as the newly stretched piece of canvas" -- and goes on to point out fascinating details for each bridge he considers. I was amazed to learn, for example, that the Verrazano Narrows Bridge in New York is so long that the curvature of the Earth makes the tops of its towers a full inch farther apart than their bases, and that when the Pont de Normandie was completed across the mouth of the Seine in France, 80 fully loaded trucks were parked on it nose-to-tail to test it before normal traffic was allowed to cross.

Two local bridges made Petroski's list -- the Arlington Memorial Bridge (he seems to have a special weakness for drawbridges) and, of course, the new Wilson Bridge which is now somewhat farther along (thank God!) than when these chapters were written.

This is not a triumphalist book. The engineering character has a certain gloomy side, a side that delights in contemplating all the things that can (and do) go wrong with structures. So we have the standard discussion of the Tacoma Narrows Bridge in Washington, whose collapse in a windstorm in 1940 was captured on film and is routinely shown to engineering students, as well as discussions of bridges that have failed during earthquakes. This is interesting stuff, especially when Petroski contrasts the way we deal with airplane failures (keep all the pieces until we've wrung the last drop of information from the debris) to the way we deal with collapsed structures (bulldoze the site and rebuild ASAP).

The last half of the book deals with an astonishing variety of other structures, from the Three Gorges Dam going up in China to the deadly collapse of the bonfire at Texas A&M University in 1999. The most interesting of these chapters was a stroll through some truly wild ideas that have been proposed by engineers in the past. My favorite: a 1928 scheme to build a dam across the Strait of Gibraltar and shrink the Mediterranean, thereby adding real estate to Europe and North Africa. (I'd like to see the Environmental Impact Statement for that one.)

In the end, what we have here is a fascinating potpourri of history, engineering and imagination, all presented in the fluid, humane writing style that we have come to expect from this author. *

James Trefil is Clarence J. Robinson Professor of Physics at George Mason University. His latest book is "Human Nature: A Blueprint for Managing the Planet By and For Humans."