Book-lover though he may be, however, Henry Petroski is, first and foremost, an engineer and so, in the end, it is the evolution of bookshelves even more than of books that fascinates him. Pigeonholes for scrolls, book presses containing thousands of chained volumes, rotating lecterns that allowed scholars to peruse more than one book at a time--these are just a few of the ingenious methods readers have devised over the centuries for storing their books: "in cabinets beneath the desks, on shelves in front of them, in triangular attic-like spaces formed under the back-to-back sloped surfaces of desktops or small tabletop lecterns that rested upon a horizontal surface." Placing books vertically on shelves, spines facing outward, is a fairly recent invention, it would seem. Well written as it is, if Book on the Bookshelf were only about books-as-furniture, it would have little appeal to the general reader. Petroski, however, uses this treatise on design to examine the very human motivations that lie behind it. From the example of Samuel Pepys, who refused to have more titles than his library could hold (about 3,000), to an appendix detailing all the ways people organize their collections (by sentimental value, by size, by color, and by price, to name a few of the more unconventional methods), Petroski peppers his account with enough human interest to keep his audience reading from cover to cover. --Alix Wilber