As one who thinks a semiconductor is a fellow in a cap who collects tickets part time, I have been searching the past year or two for a book that would describe, in simple terms, just how computers came to be developed and just what it is they do. "The New Alchemists," while no great shakes as literature, does a fine job as primer.

Here, for example, is author Dirk Hanson, explaining how electronic circuits can express Boolean logic: "Since the relays that make up circuits are two-state devices, they may be likened to little electronic traffic stations called gates. A relay in its on state can stand for a Boolean one, meaning true. The same relay in its off state represents by analogy zero, or false. Thus, in Boolean terms, the state of an individual relay represents either a zero or a one at any given moment. Used appropriately, the state of the relay gate can represent a single binary digit, or 'bit' of information -- the basic binary notation of computer theory."

So, in a single, accessible paragraph, Hanson describes the basis of computer logic -- the connection between numbers, electricity and patterns of thought.

Hanson, a journalist who has worked for Electronic News, is a fine explainer, but he is not a deep thinker. Unfortunately, he feels compelled to decorate a decent text with discussions of sociology, psychology and politics. He's continually interrupting his story to give us The Big Picture: "Someone, or some group, must be to blame for the fact that nothing is certain or simple anymore. We point the finger and look for scapegoats: How are we to orchestrate this giddy, headlong plunge into technological complexity?" Etc., etc.

As a result of such excursions, the book, a survey of microelectronics, skimps on its coverage of important topics like artificial intelligence and competition from Japan. Instead, we are force-fed treatises on post-industrial society and neo-Luddite philosophy.

But if you skim the heavy parts, you'll find that Hanson is very good at linking one development with another. By the time you finish the book, you'll understand why the vacuum tube was supplanted by the transistor and how scientists managed to jam thousands of transistors onto a thin chip of silicon to create the microprocessor. The book begins with the Leyden Jar, a glass container lined with tinfoil that seemed to capture electricity inside and fascinated Louis XV of France, and proceeds to Edison, De Forest, on to VSLI (very large-scale integration) microchips, and to predictions about what happens next.

"If supercomputers come to pass," Hanson writes, "they will be very small indeed--about the size of a softball, for optimum results, cooled in a refrigerator-sized bath of liquid helium, and performing perhaps as many as a billion binary operations per second."

As good as Hanson is at description, his book would benefit enormously from a few illustrations. The superb drawings that elucidate the article on electronics in the October issue of National Geographic could serve as a model.

Although this book is subtitled "Silicon Valley and the Microelectronics Revolution," the section on the business and the culture of the area between San Francisco and San Jose is surprisingly thin and unconvincing: "The trappings of the California life-style and the uniqueness of the microchip often obscure the fact that Silicon Valley is awash in old-school boosterism . . . There is demanding discipline, Maseratis or no."

Even in describing such rich material as flashy Silicon Valley entrepreneurs and their firms, Hanson falls flat, often lapsing into ghastly sportswriter jargon: "Helmed by the globe-trotting Jerry Sanders, AMD spends lavishly on advertising and public relations to reinforce its reputation as a young technology company on the move."

Few characters come alive, and there's no evocation of what it feels like to work at the cutting edge of technology. As a polished, rhythmic writer, Hanson can't match Tracy Kidder, author of "The Soul of a New Machine." But, in many ways, I like Hanson's book -- for all its failings -- better than Kidder's. As a primer -- a history book and elementary physics text -- it serves an important function for the home-computer hacker or the simple curious reader. It makes a difficult subject understandable. No mean feat.