John Fraser Hart is the first to admit that he’s a bit out of sync with the times.

He wears a bow tie and white shirt to class.

He tells students NOT to e-mail him.

And then there’s the old-fashioned slide projector that he uses during his lectures.

The projector, with its ancient carousel of Kodachrome slides, seems like a relic from a bygone era to his students at the University of Minnesota. But they’re willing to cut him some slack, especially since he’s been teaching the same course for almost 50 years.

“After half a century,” says Hart, a geography professor, “it’s hard to change.”

Not that he wants to.

But this week, at age 91, Hart is giving his last final exam.

Hart, who is believed to be one of the oldest professors in the country, is retiring at the end of the semester. A veteran of World War II, he started his teaching career when Harry Truman was president (1949), and joined the University of Minnesota at the dawn of the hippie era (1967).

Hunched over his walker, Hart cuts a distinctive figure on the West Bank of the Minneapolis campus, with his shock of white hair and a plume of smoke rising from his pipe. Asked why he waited until his 90s to retire, he gets a mischievous look in his eyes. “There are some people who should never be in front of a classroom; they really don’t enjoy what they’re doing,” he said. “While I’m having a wonderful time.”

As it happens, the U ended its policy mandating retirement at age 70 just before Hart’s 70th birthday. So he stayed.

But it’s hard to ignore the march of time. “I realize there are things I can’t do as well as I did 20 years ago,” he said. “When you’re young, when your memory’s not good, you write it off. When you’re older, you think maybe the gray cells are disappearing.”

Still, he says, “I hope the students don’t recognize it.”

His students say that his courses are not for the faint of heart. Known for his “blunt demeanor,” he’s even bragged that a third of his students fail his first exam.

“He’s a firecracker,” said Nicole Mardell, 22, a senior. “The first day he walked in with his bow tie, glasses and walker, and we all kind of wanted him to adopt us as his grandchildren. But then after the first lesson we realized he was sassy and could probably beat you in any argument.”

The accidental teacher

Hart once vowed that he’d never spend his life in a classroom. The son of a history professor, he grew up in Virginia during the Depression, earned a degree in classical languages at 19, and found himself as a naval intelligence officer on an aircraft carrier in the Pacific in World War II. Part of his job was teaching sailors to distinguish enemy aircraft from friendly ones; but he found his students “sullen, uninterested, bored, unmotivated.”

Back home, “I told my mother the one thing I learned in the war was I never wanted to be a teacher.”

But his wartime experience awakened an unexpected passion. “We were part of the fleet that occupied Japan,” he said. “I saw a lot of geography, and I was curious about it. I wanted to know more about the places I’d been.”

He ended up earning a Ph.D. at Northwestern University, where he met his wife, Meredith, and in 1949, started teaching at the University of Georgia.

Hart knows that, to some, geography conjures dry images of maps and atlases.

He jokes that, when people would ask him about his field, “I used to say I have 12 definitions of geography, depending on how interested you are and how sober you are.”

At its core, he said, geography is about understanding the world. “People are what make geography interesting,” he said. “I try to talk about people and how they’re living and how they’re influencing the world.”

The geography of manure

For decades, he crisscrossed the United States and Canada, snapping photos of people adapting to the land, and vice versa. He was especially fascinated with agriculture, and how urban sprawl threatened the rural life cycle.

Once, he published a paper on the geography of manure. “City people don’t realize how important it is, [and] country people take it for granted,” he explained. “I wanted to help city kids know where their food comes from.”

His seminal book, “The Land that Feeds Us,” came out in 1992. But his “restless mind,” as one colleague puts it, led him down unpredictable paths. In 2002, he co-wrote a book about trailer parks, called “the Unknown World of the Mobile Home.”

Why mobile homes? “They’re the most affordable houses that we have in our society,” he said. “And nice people don’t know anything about trailers. Most Americans want to pretend they don’t exist, and people who live in them have a little bit of a chip on their shoulders.”

In his fieldwork, he liked to blend in with his camera and curiosity, asking people to share their stories. Along the way, he amassed some 25,000 photographs, which formed the basis of his signature course, the Geography of the U.S. and Canada.

Last week, he ambled into class at 10 a.m., toting a battered case with the day’s slide show, and settled into the back of the room next to the projector. At precisely 10:10, he flicked off the lights, clicked on the first slide, and without so much as a “Hello,” began a 50-minute monologue. “Most irrigation systems use ditches to get water …”

He delivers his commentary without notes, in a steady monotone, about the struggle of farmers in the desert Southwest, or “oases” like Phoenix that have sprouted in a place with no water. “In the fall, the license plates change color, not the leaves,” he says.

It’s a teaching style that leaves little room for questions, much less computers, iPads or technology that’s common in other classes.

“The whole setup reminded me of the way my dad would show slides of our family trips,” said Ian Jacobson, a 20-year-old sophomore. “I got used to it quickly, and really ended up liking it.”

Not everyone does, says Hart. “Some like it. Some hate it, some tolerate it.” One student told him his mother had taken the class when she was a student. “I said, ‘Did she like it?’ ’’ Hart recalled with a laugh. “He said, ‘She hated it, too.’ ”

No trendsetter, or follower

But it’s what makes Hart’s classes so remarkable, says John Adams, a retired U geography professor and longtime colleague.

“He teaches the kids how to look at the land and how to see things that they’ve gone by a hundred times and never noticed,” he said. “He doesn’t capitulate to trends or to expectations.”

Hart’s department chair, Abdi Samatar, says he sat in on the class to see why it’s so popular. “When he talks about the U.S. and Canada, he knows every square meter of that land,” Samatar said. “It looks like somebody telling a story, but it’s a story loaded with knowledge, loaded with meaning, and loaded with firsthand experience.”

In lieu of a retirement party, Hart delivered a “farewell lecture” for colleagues at an April symposium. “I called it ‘Old Haunts Revisited,’ ” a greatest-hits of his famous course.

With Hart’s retirement at hand, the U is trying to preserve his classroom legacy. Archivists have begun digitizing thousands of his slides, and Hart has been recording some of his lectures in a studio. Samatar says the goal is to put them online in some form.

“So Fraser will retire in person,” said Samatar. “But his ideas and the course will not.”