John Hamilton turns 100 later this month. But he hasn’t spent much time thinking about it. He’s too busy with other things — like discovering how magnetism works.

Hamilton does his research in a tiny 8-by-8 workshop that takes up most of the main room of his Cedar River Terrace apartment.

There’s two work benches, drawers, shelves and a band saw. In the bedroom is a bench grinder and a “half-baked lathe,” plus a closet full of “accumulated junk.”

It’s all on wheels, and Hamilton built it all himself, out of throw-aways he pushed home in a shopping cart from McLendon’s, once just down the street from Cedar River Terrace.

“I built all this junk here,” Hamilton says, wheeling over to the workshop on an office chair, on a recent day in his apartment.

He flicks a switch and a machine hums to life. “See this, that’s the band saw, and it works good,” he says.

Hamilton initially used his workshop to furnish his apartment. A table to eat on; a coffee table; shelves to hold books, movies, a tape deck, busted CD player, a TV and VCR.

But furniture isn’t why Hamilton built his workshop.

“I built it so I could try and prove things I thought about, whether they’re true or not,” he says.

His studies have taught him how magnetism works. Magnetism is used in everything, but very few understand it, he says. And those who do, understand it wrong. At the crux of Hamilton’s discovery? Magnetism and radioactivity are related. He says this knowledge will help build better, stronger magnets. He’s already made an-inch square magnet that can pick up 100 pounds. Before he dies, Hamilton hopes to get his findings down in a book, or pass them onto someone trustworthy.

He curses the timing of his breakthrough.

“I’m just at a point now when I could really do something that could be important, but I can’t see worth a damn, and my hands don’t work how they should. I’m limited by my physical situation.”

Hamilton is legally blind and has neuropathy, a painful nervous-system disorder. But it’s not like magnetism is the only important thing he’s done in his 100 years.

As he says, “I’ve had my fingers in about every kind of pie you can imagine.”

Hamilton’s lifelong learning began early. He remembers, as a young boy in San Francisco, pressing his face to the window of a motor-repair shop for so long that the shop owner invited him in. The owner, a German named Koontz, taught him about motors. Then Hamilton moved on, to learn about something else.

“I have a habit of finding out what I want to know about something and passing onto something else,” he says.

“I find that everything is interesting — everything,” he adds. “There’s no limit. You can go from thing to thing.”

And so he has. At 13, after a childhood spent bouncing from hotel room to hotel room (his seven-time married mother was a maître d’); boarding school to boarding school; and state to state (he was kidnapped five times, by his grandma and then his mother, who each wanted him in their care), Hamilton went to sea as a wireless (radio) operator. He traveled the world twice, while keeping ships in contact with other ships and ports.

After his sea-life, Hamilton took work at a phone company. He also taught math at the California Institute of Technology, and earned a doctorate in physics from Columbia University, plus degrees in chemistry and electrical engineering.

He did chemical work for a doctor of spectroscopy, which is the study of spectrums. Hamilton also repaired ships bombed during World War II, and helped develop the atomic bomb in the desert of Oak Ridge, Tenn.

He even had a hand in the classic Hollywood movies that he and his caretaker and friend Nancy Clow watch on his TV every evening. He helped develop a system for coloring movies, based on natural color. But the industry ultimately chose a system that allowed for more vibrant colors.

In addition to learning through his jobs, Hamilton has had many “back door” learning experiences, like his early stop at the motor-repair shop. He learned about blueprint paper and printing presses by entering shops through the back doors. He learned about anesthetics and how to set a broken leg by helping a doctor when no one else was around.

Hamilton’s also had “front door” learning experiences, like when he met Einstein.

Hamilton was studying near Philadelphia, Penn., when he had a physics problem. Books were no help. “You need to talk to Einstein,” said the head of Princeton University’s physics department.

Hamilton had his doubts, but went to Einstein’s Princeton house and knocked on the door. A woman let him in, then fetched Einstein.

“He looked like a farmer,” Hamilton recalls. “He was wearing slippers. He wasn’t wearing overalls, but loose garments. And his eye twinkled — he’d look at you like everything is funny.”

Einstein being Einstein, he answered Hamilton’s questions. But not in the traditional way.

“He led you around until you stumbled over the answer, and you learned what you needed to know,” Hamilton says.

Hamilton may have talked to physics royalty, but it felt rather everyday to him.

“Damn few people got that opportunity, but I didn’t know that at the time. It seemed like a normal thing to me,” he says.

Hamilton was married, until his wife died of cancer in 1950. He’s outlived four of his six children. His two daughters and his daughter-in law will attend his 100th birthday party, July 31 at Cedar River Terrace. Clow expects up to 100 guests.

Meanwhile, he has his studies and thoughts to keep him busy.

“Being busy is important,” he says. “If you’re not busy, all your pains get bigger.”

Doctors say Hamilton could keep busy for 10 more years.

“The doctor said, ‘I don’t know what you’re doing, but keep it up,” he says.

He plans to. The neatly dressed Hamilton looks younger than his near-100 years. He has a head of wispy white hair, plastic glasses and house shoes held together with yellow duct tape. On this recent day he’s wearing a blue striped shirt and black pants. He gets around on his wheeled chair, or with his three-legged walker for longer trips, like out to his car.

A state caregiver helps him three days a week, and Clow helps him the rest of the time. She makes him lunch and dinner every day.

Hamilton’s mind also seems much younger than 100.

“I learn something every day,” he says.

He once made a list on an adding machine of all the “pies” he’s stuck his fingers in.

“I wrote and wrote and wrote, and I had a list like this,” he says, stretching his arms in opposite directions as far as they go. “Then I said, ‘To hell with this, no one will ever believe this.”