Horowitz could find neither knife nor volunteer, as both grad students declined his invitation. "We're not your grad students," they said. "We're only on loan." But he was determined to analyze some blood, and after sterilizing a probe he began testing his fingertip gently. His resolve waning, he wondered aloud, "Is this the way you do it?"

Reasoning that a puncture would be less painful where there were fewer nerves, he pulled up his left pants leg, exposing a skinny calf and a sagging sock, and began scraping. The cut was not clean, and Horowitz forced a muttered "fuck." The grad students smiled.

Only after removing several layers of skin did Horowitz squeeze out enough blood to make a sample. The analysis showed large amounts of iron--again, just what he expected. Horowitz prepared to leave.

He called to rearrange his shattered schedule, cancelling the original lunch date and making a new one with his morning appointment, the owner of a small company who wanted to hire Horowitz as a consultant. Now he felt rushed, but before turning the proton microscope over to the grad students, he reviewed safety precautions and shutdown procedures.

The students were impatient again, and joked about "just pulling every plug" they could find, but Horowitz didn't laugh. He thought of how expensive replacing a delicate exposed membrane on the counter would be. It might cost thousands of dollars, money he and his grant did not have. He has never broken anything more expensive than a large Bell jar, but knows that he has often been more lucky than careful.

Because Horowitz understands how every valve, scope and gadget in the lab works, he doesn't like to take chances. He remembers the way some of the lessons were learned. There was the explosion that splattered him with acid when he was very young, and tried some experiments with batteries. And there was a severe shock in a lab several years ago, when a powerful charge ran in a complete circuit from one arm to the other, passing through his heart. He was almost knocked unconscious, but his first thoughts were, "What went wrong?" He quickly realized that there were two ways to install a fuse, and one of them could lead to accidents like his. "That's probably the best way to learn," he says, laughing.

But Horowitz did not have time to joke now, and he quickly gave the graduate students some last-minute instructions on how to shut off the helium supply and checked out. He turned in his radiation counter--he hadn't absorbed much today--and was ushered out the back door by a security guard, a reminder of the classified work that goes on in the labs, an old radar-research center from World War II.

For about two seconds after Horowitz started the engine, there was a high pitched hum, a noise that ordinarily warns of an open door or unused seat belt. But all the doors were shut, and the belts were snapped into place Horowitz glanced at the dash. The hum stopped, and he drove on.

Horowitz had rewired his car so that the seat-belt warning sounds when the oil pressure is low. "That's much more important to know," he says, "and besides, I figure we'll wear seat belts anyway." He hooked up another switch to a fan, so he can cool his engine in heavy traffic, but otherwise he hasn't meddled with the European engineering, which seems clever to him.

He is only just learning about cars, because unlike most teenagers who grew up in New Jersey in the late 1950s, he spent little time tinkering with engines or hanging around parking lots. When Horowitz turned 16, he didn't rush out to get his license--he picked it up a couple of years later. Cars didn't seem fun. Neither did boy scouts, football games or proms, the things most of his schoolmates liked.

Horowitz enjoyed technology. He wasn't attracted to radio by the prospect of making small talk with other hams--he liked fiddling with the dials. One of his earliest memories is electronic--he and his older brother found pebbles with flecks of metal in their driveway in Elizabeth, N.J., and used them as crystals for radios. Then seven, he was astounded that science touched something as mundane as a rock in his driveway.

His parents, a textile manufacturer and a marriage counselor, felt a thrill of their own. "They thought they had a young genius on their hands," Horowitz recalls. "They still think so."

They discussed the best way to educate Horowitz, and decided to keep him in the public schools when they moved to Summit. His mother, who skipped grades when she was young, decided that her genius son would not. So he went through school one grade at a time, taking the same courses as everyone else, and enjoying them with no hint of impatience. And after the last bell, he would rush home to his basement workshop, where he kept his rockets, photographic equipment, radio rig and chemicals, where he blew up the battery, and where the sink had lost its protective coating to acidic solutions Horowitz poured down the drain. His parents left him alone, realizing that he knew more about what he was doing than they did. Once, though, they cautioned him after his brother accused him of carelessness. Horowitz resented it. He was only having fun.

From the beginning, Horowitz wanted to be an engineer. He liked figuring out how gadgets worked, and improving them. While other would-be geniuses were building rockets that looked like real missiles down to the decals, that spun into the sky spitting fire from their bottoms, Horowitz and his brother realized that without a guidance system a rocket had to be pulled, not pushed, to fly straight. So they mounted their home-made engines at the front of long rods, like the old Chinese fireworks, and sure enough, they went straight up. Horowitz took photographs to prove it.

In high school, teachers reacted to him with a quiet hysteria. He was put on independent studies in English courses, even though he thinks now he was only an average student outside of science. But no one wanted responsibility for holding back a genius, the boy who didn't just look through the microscope at onion skin cells, but also took photographs of them; who didn't just take postcard pictures, but tried to blow them up to enormous wall murals. He was oblivious to the fuss, just as he never wondered whether he would rather be athletic or glib with girls than be alone in his basement so much of the time.