Recently, a reader asked what I consider to be the seven greatest wonders of the world.

When I drew up my personal list, I limited it to acts of nature and natural history that I've seen, such as gorillas in the wild and the eruption of Mount St. Helens. But the world has many other kinds of wonders, including astonishing ideas, influential inventions, artistic creations and architectural marvels such the Great Pyramid of Egypt.The Great Pyramid is, of course, one of the original "seven wonders" of the ancient world. It's the oldest -- 4,500 years old -- and the only one that still exists. The Hanging Gardens of Babylon, said to be a breathtaking spectacle 2,600 years ago, may never have existed. The other five ancient wonders -- two statues, a temple, a marble mausoleum and a towering lighthouse -- were built between 2,200 and 2,500 years ago and fell victim to earthquakes, plundering and other calamities.

Any list of wonders is very subjective, and there's really no way to compare different kinds of wonders. Which is greater, the Taj Mahal or aspirin? The Grand Canyon or calculus?

I'll list my seven favorite natural wonders, followed by a sampling of wonders of very different kinds.

1. Gorillas, chimpanzees and orangutans are thrilling to watch in the wild. These anthropoid apes at times seem almost human. I saw gorillas in Zaire, but nowadays people also go to Uganda. Tanzania is where you see chimps in the wild. Orangutans live only on two Indonesian islands, Kalimantan and Sumatra.

2. The Amazon River includes a vast tropical plain, which at times is as much as 30 miles wide. Until I visited, I didn't realize that there are forests where the base of the trees are always submerged -- in a river that runs very slowly because it is so wide and amazingly flat (a drop of just a few feet over several miles). The resulting life cycles are unknown elsewhere in the world. Monkeys live in treetops and don't come down because there's no ground to come down to. Birds are present in more varieties than anywhere else in the world.

3. Yellowstone National Park is singular, too. Heat bubbles up from inside the earth in more than 3,000 places, and the minerals deposited by the scalding water form multicolored cones and other shapes. Old Faithful, the best-known geyser, erupts on average about once every 65 minutes, although the interval varies.

4. Guilin, China, has been a center of Chinese art for centuries. Picturesque limestone hills rise abruptly along the banks of the Li River and often are shrouded in fog. The hills have surprisingly vertical sides and yet often have rounded tops. When you think of Chinese art, if you visualize steep-sloped hills along a river, you're recalling scenes from Guilin.

5. I loved snorkeling in the Great Barrier Reef, off the northeast coast of Australia. My friends who know scuba diving say that Belize or Papua, New Guinea, are even better.

6. I looked out my office window one morning in 1980 and saw Mount St. Helens erupt, about 100 miles away. It was the most powerful demonstration of the fury of Mother Nature that I've ever seen.

7. Until you've seen the Grand Canyon, you don't really get a sense of its immensity. It's BIG.

Maybe if I had traveled to more of the world's natural wonders I'd have a substantially different list of favorites. The Nordic countries are famed for their fjords, narrow bays that wind far inland between steep walls of rock. I haven't seen them, though. I've missed a lot of artistic and architectural wonders, too, including the Great Pyramid.

As for ideas and innovations, many achievements older than the Great Pyramid have had wondrous consequences. The domestication of plants and animals, the invention of written language and the discovery of mathematics are enduring wonders.

Recently, author and literary agent John Brockman posed the question, "What is the most important invention in the past 2000 years?" He received thoughtful and often surprising answers from more than 100 leading thinkers, a fascinating survey of intellectual and creative wonders of the world.

Some people nominated inventions that were influential in bringing the world to where it is today, such as the printing press, calculus, the invention of the scientific method and effective contraception.

Other interesting suggestions included anesthesia, double-entry accounting, plumbing and sewers, reading glasses, batteries, the concept of education, self-governance, probability theory and the notion that mathematics could be used to represent things.

Christopher Langton, a computer scientist, proposed the telescope, which "opened the doors to the flood of data that would resolve what were previously largely philosophical disputes."

James J. O'Donnell, professor of classical studies at the University of Pennsylvania, proposed modern health care -- from antibiotics to medical techniques to the soap that doctors use to wash their hands.

"Review your own life and imagine what it would have been like without late-20th century heath care," he wrote. "Would you still be alive today? An astonishingly large number of people get serious looks on their faces and admit they wouldn't."

Douglas Rushkoff, a writer and teacher, proposed "the eraser. As well as the delete key, white-out, the constitutional amendment and all the other tools that let us go back and fix our mistakes."

Tor Norretranders, a Danish science writer, nominated the mirror, which became commonplace during the Renaissance. "Only with the installation of mirrors in everyday life did viewing oneself from the outside become a daily habit," he wrote. "This coincided with the advent of manners for eating, clothing and behavior. This made possible the modern version of self-consciousness: viewing oneself through the eyes of others, rather than just from the inside or though the eyes of God."

Howard Gardner, professor of education at Harvard University, proposed classical music. "Most inventions -- from nuclear energy to antibiotics -- can be used for good or ill," he wrote. "Classical music has probably given more pleasure to more individuals, with less negative fallout, than any other human artifact."

Other people nominated inventions for the promise they hold for the future. The computer, the Internet and biotechnology were leading candidates.

"The Internet will dissolve away nations as we know them today," wrote Clifford Pickover, an IBM researcher. "Humanity becomes a single hive mind, with a group intelligence, as geography becomes putty in the hands of the Internet sculptor."

Lawrence Krauss, who chairs the physics department at Case Western Reserve University, wrote: "While the printing press certainly revolutionized the world in its time, computers will govern everything we do in the next 20 centuries. . . . The only other invention that may come close is perhaps DNA sequencing, since it will undoubtedly lead to a new understanding and control of genetics and biology in a way which will alter what we mean by life."

"Ultimately," said Robert Shapiro, professor of chemistry at New York University, "we may elect to rewrite our genetic code text, changing ourselves and the way in which we experience the universe."

I agree that gaining a complete understanding of the genetic code will be the greatest human achievement. It will show us exactly how the mind and body work, and open exhilarating and scary possibilities. We haven't achieved this understanding yet, but we will.

The entire list of nominated inventions is posted on the Internet at (www.edge.org). Reading them reminds me of how wondrous our world is.

Questions may be sent to Bill Gates by electronic mail. The address is askbill@microsoft.com. Or write to him care of the New York Times Syndication Sales Corp., 122 E. 42nd St., New York, NY 10168. Bill Gates regrets that unpublished questions cannot be answered individually.