Twenty years ago Nicholas K. Sheridon got his big idea, the kind that scientists--if they are talented and fortunate--get just once or twice in a career. Sheridon hit on a way to draw images electronically that would be far more portable than heavy cathode-ray tubes, far cheaper than liquid-crystal panels. In theory, his invention could bring to digital displays many of the advantages of paper. They would be thin and flexible yet durable. They would consume only tiny amounts of power yet would hold images indefinitely. They could be used for writing as well as reading, and they could be reused millions of times. Yet they would be as cheap as fine stationery. Sheridon named his idea Gyricon, and he applied for and received a patent on it.

But there his good fortune failed him. Twenty years ago Sheridon's managers at the Xerox Palo Alto Research Center were sitting on many of the inventions that would eventually propel the personal computing revolution: the windows and mouse interface, the laser printer, Ethernet. Like those innovations, Gyricon drew only yawns from Xerox's blinkered managers. "The boss said, 'Xerox really isn't interested in displays. Why don't you work on printing technologies?' So I did," Sheridon recalls.

Fifteen years later the soft-spoken scientist returned to his inspiration, and today the incarnation of his idea sits flashing the PARC logo in black-and-white on his desk. Although it is an early prototype, the 15-by-15-centimeter device is quite legible and thin. More impressive is the fact that the device is powered entirely by a pinky-size solar cell. When Sheridon removes the power altogether, the logo stops changing shade, but it does not fade.

Gently peeling a sheet off its plastic backing, Sheridon shows me what Gyricon is made of. The material is no thicker than a latex glove, and it feels about as rubbery. That is no coincidence: the substance is made by mixing tiny plastic balls, each just 0.03 to 0.1 millimeter in diameter, into molten, transparent silicone rubber. Every ball is white on one side, black on the other. Cooled on slabs and cut into sheets, the rubber is next soaked in oil, which it sucks up like a mop. As it does, the sheets expand and oil-filled pockets form around each ball, which can then float and rotate freely.

Through a chemical process that Xerox is holding as a trade secret, "each ball is given an electric charge, with more on one side than on the other," Sheridon explains. So when an electric field is applied to the surface of the sheet, the balls are lifted in their oil-filled cells, rotated like the needles of tiny compasses to point either their black or their white hemispheres eyeward, and then slammed against the far wall of the cell. There they stick, holding the image, until they are dislodged by another field. At high voltages, the balls stick before completing their rotation, thus producing various shades of gray. Sheridon's group has also produced red-and-white displays and is working on combining balls of various hues to produce full-color ones.

In his early work on Gyricon, Sheridon had figured out everything except a cheap way to make billions of plastic balls, all colored on one side only and all the size of a pinpoint. "This is the secret," Sheridon says, holding up a steel disk slightly smaller than a CD. The disk is spun on a spindle at 2,700 rpm. White plastic is pumped onto the top of the spinning disk, black onto the bottom. The plastic streams skitter off into jets that join at the edge and break up into precisely bicolored, spherical droplets.

Sheridon has demonstrated that the Gyricon material remains stable after more than two years and three million erasures. His group has built displays at resolutions of up to 220 dots per inch (200 percent finer than most LCDs) and sizes up to a foot square. "We would like to get higher resolution and better whiteness," Sheridon admits. "But we know how to do that: make the balls smaller and pack them more closely."

For certain applications, such as large commercial signs, the technology appears to be only a few years from market. Gyricon displays might find their way into laptop and handheld computers soon after that. "It would probably allow you to run a laptop for six months on a few AA batteries," Sheridon says, because the device requires neither a backlight nor constant refreshing, as LCDs do.

But the real goal, Sheridon says, is also the most distant: an electronic surrogate for paper. Engineer Matt Howard hands me a wooden pencil that is plugged into a weak power supply. As I write on the sheet, the tiny electric field conducted through the pencil's graphite core darkens the screen wherever the tip touches. Howard is working on a handheld wand that will receive text and images from a computer and scan them onto a Gyricon page, which would then be annotated, photocopied, erased--but not discarded.

The effect of such an invention on business--especially Xerox's business--is hard to overestimate. Had PARC been more farsighted, or Sheridon more ambitious, would electronic paper have become commonplace a decade ago? Quite possibly. As it is, Gyricon now must compete with liquid crystals and electrophoretic displays (which use charged particles of one color suspended in liquid dye of another) being developed by the Massachusetts Institute of Technology and E Ink in Cambridge, Mass. Sheridon grimaces briefly as he concedes, "It's a horse race."

--W. Wayt Gibbs in Palo Alto, Calif.