Steve Wozniak (who designed the Apple II computer), Dean Kamen (who built the Segway personal transporter) and Jay Walker (who devised the name-your-price business model of are among the inventors profiled in Evan I. Schwartz's new book, "Juice: The Creative Fuel That Drives World-Class Inventors." Schwartz, whose last book was a biography of television pioneer Philo T. Farnsworth, talked with NEWSWEEK's Jerry Adler.

ADLER: You quote Jay Walker on how inventing is like solving a Rubik's Cube: "Here's a six-sided figure, and getting five of them right doesn't help you." Actually, if you get five sides of a Rubik's Cube right, the last one is automatically right, also, isn't it?

SCHWARTZ: Correct.

So how come he's rich and I'm not?

I don't know. I think I misquoted him. He must have said four, not five.

What three recent inventions exemplify the kind of conceptual breakthrough you talk about in your book?

The first one that comes to mind is the use of computers for communications. Everyone thought that since they were called computers, they were there to compute things. Gene sequencing is another example--viewing the body as information. I write about Leroy Hood, the co-inventor of the machine that made the Human Genome Project possible. That was an invention that doesn't just cross disciplines, it transcends them. An area that's still developing is the hydrogen fuel cell. We've known --about it for a long time, but one guy, Geoffrey Ballard, is trying to make it economically viable for automobiles.

So the conceptual leap isn't technological.

No, it's a systems problem. He's working on the problem of manufacturing and transporting hydrogen, making it practical to just pull up to a pump and fill up your car. That's not a trivial problem, by the way. You have a lot of societal inertia to overcome. Henry Ford wasn't competing with anything except the horse, and that wasn't much of a contest. Now you have this whole installed base of gasoline refining and transporting and internal-combustion engines to burn it. People won't buy the cars unless they can find fuel for them, and companies aren't going to invest in a distribution system until there are cars. Solving that requires the same kind of creative mental energy as inventing a new machine in the first place. My term for it is "juice." Ballard has it; he's been at this for 30 years, and he's not stopping now.

You mentioned cars. Inventions over the past 25 years have revolutionized computers, electronics and medicine. Cars and airplanes haven't changed much. Have we hit a plateau in transportation innovation?

Not necessarily. You don't know where things will end up. Like the Segway. Who knows what the killer app will be for that? I don't think Dean Kamen knows it himself. It could be in China that it takes off.

So what qualities does a successful inventor have?

One quality that stands out: it's the ability to find new problems that no one else even sees. The conventional view of inventors is, they're good at solving problems. It's really finding problems. Max Levchin was an expert in cryptography. Everyone thought there needed to be a secure way of paying people on the Internet. There were dozens of start-ups that failed because their solutions were so complicated. They required you to download a cryptography application onto your desktop and run the program every time you wanted to pay for something. People didn't want to do that. So he came up with PayPal, where all the security features reside on a server, and the customer just sends an e-mail. He saw this problem in a completely different way. That's what inventors do. They ask: how can I make this better?