Robert Ehrlich teaches physics at George Mason University. This is the third book by him that I have read recently. The other two, "Turning the World Inside Out And 174 Other Simple Physics Demonstrations" (Princeton University Press, 1990, $16.95-paper) and "The Cosmological Milkshake: A Semi-Serious Look at the Size of Things" (Rutgers University Press, 1994, $30.00-cloth, $14.95-paper) are also recommended. Ehrlich's sense of humor and his willingness to speculate about science make this book both a treasure trove of practical physics and an inspiration to teachers of science. Naturally, most of the subject matter is "physics", but one can hardly argue that speculation about, for example, the magnitudes of Planck's constant and the speed of light, or the question in the book title, is irrelevant to chemistry. You might want to disagree with his some of his answers, but I suspect he would encourage you to.