On July 22, 1979, the town of Greenville, New Hampshire, witnessed a feat it would never forget.

It all started when the police started to notice crowds gathering along the banks of the Souhegan River, directly under the Greenville Span. This railroad line, which once connected the town to Fitchburg, Mass., held the record at one time as being the tallest span in all of New Hampshire. Time and disrepair, however, had turned it into a useless relic.

When the police began to question the bystanders, all they got were vague responses. That’s when a small plane came down the valley, and after a couple of practice runs, flew directly under the span.

The pilot who completed this amazing stunt was one Bronson Potter, an eccentric inventor and hermit from Mason, who had made his fortune inventing the timer for the Polaroid Land Camera back in the 1960s. The authorities were definitely not amused, and the Federal Aviation Administration temporarily pulled Potter’s pilot’s license.

Now, four decades later, the public is invited to relive this astonishing feat on Aug. 9, as newly discovered 8-millimeter footage of the flight will be unveiled at Mason Elementary School.  The event is sponsored by the Aviation Museum of New Hampshire, the Mason Conservation Commission and Back Lot Films. Music will be provided by a local bluegrass band, the Dirty Double Crossers.

“The film was taken by local resident David Morrison, who was very excited about the event at the time,” said Jeff Rapsis, executive director of the Aviation Museum. “But the film was put away for 40 years, and only recently came to light.”

Rapsis said that this event is part of the museum’s ongoing initiative to highlight aviation landmarks throughout the state.

“We really want to celebrate great aviation legends of New Hampshire,” he said. “We already have exhibits about Bernice Blake, the first female aviator in the state; the astronaut Alan Shepard, who came from Derry; and Christa McAuliffe, who was on the Challenger space shuttle. For such a small state, we really have a large legacy when it comes to aviation.”

Well-known as these names are, Rapsis said that he wanted to focus on lesser known, but nonetheless interesting items far abreast of the Manchester area.

“I was aware of Mr. Potter’s feat, where he flew under the railroad trestle,” he said. “I really didn’t know much more than that, but it wasn’t hard to find tributes online. What really struck me was that, when he passed away in 2004, his gravestone in Mason featured an illustration of him performing this feat.”

Smelling a story, Rapsis decided to dig further in, and reached out to the historical commission and residents of Mason, to see if there was interest in a presentation on the event.

“I soon found that people were reluctant to travel all the way out to Manchester, but there would be interest in a local event in Mason,” he said. “From there, it blossomed into a situation where a number of people expressed interest, including David Morrison, who dug out his old movie reels, which we then transferred to DVD.”

Rapsis said that the movie is a real time capsule, with some unexpected surprises.

“There are about five minutes of film altogether,” he said. “Some of it was taken from underneath the trestle, and other parts from on top. It appears that there were two reels of film that were edited together.

“The first shots show people gathered together on Route 31 and the bed of the Souhegan River, waiting for something to happen. It’s a real blast from the past, as you see how people dressed in rural New Hampshire in those days.

“Then the plane appears, and Potter makes a few dry runs at the bridge, just to get his bearings. The suspense builds as he gets ready, then there’s the ultimate payoff where he flies the plane directly under the trestle, which is a very narrow space for an airplane.

“The actual feat is shown from two different angles, where you see the plane from above, and then from underneath. The sense of exhilaration that everyone must have felt is still tangible when you look at this footage.”

Rapsis said that this is a rare opportunity to view a real piece of New Hampshire history, and get a sense of what it must have been like to be there.

“This is remarkable, because it’s something people saw, which has since passed into legend,” he said. “What’s amazing is that we have this film, so that anyone who wants to see this after 40 years can witness it for themselves.”

The world premiere of recently rediscovered home movie film of Bronson Potter’s 1979 Greenville Trestle Fly-Under will be held Friday, Aug. 9, at 7 p.m. at Mason Elementary School, 13 Darling Hill Road, Mason. The program is free, and the public is invited; sharing of Bronson Potter stories will be encouraged. For more information, contact Jeff Rapsis at 236-9237 or jrapsis@nhahs.org.