Michigan Tech's entire physics faculty will be recognized by Guinness World Records in the next edition of its famous book, a mere 103 years after their record-shattering feat.

While researching the department's history, physics professor Bryan Suits discovered that four former faculty members, including James Fisher, Nathan Osborne, Elmer Grant and Fred McNair, had built several 4,000-plus feet (1.3 km) pendula in the old Tamarack Mine shafts near Calumet back in 1901. Impressed, Suits contacted Guinness and found that their current record pendulum was only 22.5 meters, about 75 feet. "I said, 'Maybe you'd like to hear about ours,'" Suits recalls.

McNair, who was president of the then-Michigan College of Mines, and his colleagues did not build their pendulum to set any records. "The whole reason they were doing this was to map out what was going on in the mines," Suits said. The mining company had just dug a new shaft, the No. 5--at over 4,000 feet deep, the Tamarack shafts were then the deepest in the world--and they wanted to dig a tunnel between the new shaft and a tunnel from another shaft.

That maneuver, while common in underground mines, had never been tried at 4,000-plus feet. The shafts were hundreds of feet apart, the copper was somewhere in between, and the risk was that miners would tunnel in the wrong direction and miss completely.

For help with the problem, the mine engineers called the experts, and the physics faculty put together a plan. Using steel piano wire, they would hang two plumb lines in each shaft, with 50-pound weights at the bottom. This would allow them to establish reference lines at the bottom of the shafts, so that miners could dig tunnels at the bottom and eventually link up.

"This was standard mining stuff," Suits says. "It's just that no one had ever done it anywhere near this deep before."

Once the lines in No. 5 were in place, McNair's party was lowered to the bottom of the shaft. "I saw a picture of how they actually got down there; it was called a man cage," Suits says. "It's not very big, and it doesn't actually have doors on it or anything."
Once they got there, one of the first things McNair's team did was measure the distance between the plumb bobs at the bottom. Theoretically, they should have been the same distance apart as the lines at the top or perhaps slightly closer, given the curvature of the earth. McNair was surprised, then, to find that they were about an inch farther apart.

The second thing they did was to push the bobs aside and let them swing, "exactly what you would expect a physicist to do," said Suits. A full swing took a bit over one minute.

The group also tried experiments with falling objects and performed ultra-precise measurements of the force of gravity as a function of depth. The group addressed the mining problem using pairs of plumb lines in the No. 2 and No. 4 shafts, finding similar results. The longest pendulum they reported was 4,440 feet in shaft No. 4, and it is this pendulum that will be memorialized by Guinness World Records.

The story was picked up in the popular press, including the Daily Mining Gazette, which reported that forces such as magnetism, or even some new physical phenomenon, might have caused the plumb lines to diverge.

"In the early 1900s, people were really into science," Suits said. "It was quite amazing. The Gazette article was very technical. People then were just seeing technology in their daily lives and were very interested in how science was going to affect them in the future."

Then as now, people were also into pseudoscience. "This got the hollow earth people excited," Suits said. "They thought we were living on the inside of a sphere rather than on the outside."

The pseudoscientific interpretations still exist, apparently. If you run a search on the Web for the words "Tamarack mine" and "plumb," you can find references to the experiment along with arguments that, for example, the earth's center of gravity is 4,000 miles out in space.

After making extensive measurements, the actual explanation of the diverging plumb bobs proved a bit more pedestrian. McNair published his findings in Science, concluding that the natural air currents circulating in the shaft caused the lines to hang a little off center.

For Suits, the charm of the story lies less in identifying the world-record pendulum as in visualizing MTU's former president poking around in a hole almost a mile deep in the rock. "Here you have Fred McNair, the president of the college and a Fellow in the American Physical Society, and three other good physicists. And they are all at the bottom of this mine making measurements and getting dirty."

They didn't even go down there to do science, he notes. They were just helping to solve a mining problem. "But it became curiosity-driven research," he says. "So they did what any good scientists would do. They thought, 'No one's been down this deep before; let's see if there's anything unusual going on.'"