In 21st century books, computer chips will replace wood-chips. This book could be the only one you'll ever need and the last one you'll have to buy.

It is a single volume, electronic book which contains a library of information, or all the books on the best-sellers list. When you are finished, you could fill it with new books.

Why would you want an electronic book? Because they don't take as much energy as a lap-top or similar portable information devices, they aren't difficult to read in sunlight, and they are portable. The idea was developed in the Massachusetts Institute of Technology's Media Lab by a team led by physicist Joe Jacobson. It will probably be a few years before these books are in stores because of problems relating to large-scale manufacturing.

Here's how it works, according to Popular Science: Each paper page is coated with millions of microscopic particles encased in tiny capsules. Each micro-capsule can react independently to an electronic charge. Depending on the type of charge applied, they can be black (negative), or white (positive).

One microcapsule is about half the thickness of a human hair. The smaller the letter, the greater the number of capsules used, which improves resolution. The capsules can change color quickly, to give the effect of motion.

The main attraction of this book is convenience. It is portable, you can change the type size to read it more easily, and you can record your own notes electronically in the margins. Only a small battery is needed to view it after it is typeset, and you can store your observations on removable flashcards in the spine.

Even though this book won't be available for a couple years, you might want to save for it now. It's going to cost around $200 for a basic read-only model, and up to $400 for one that lets you record your comments. I don't know about you, but I wouldn't mind having a motion picture changeable book! u