Bank’s pendulum, only one in state, shows Earth’s rotation

How many people know that the only Foucault’s pendulum in Montana is located in downtown Billings, in the Western Security Bank building?

For that matter, how many people know what a Foucault’s pendulum is?

Basically, it is a simple device that demonstrates that the Earth rotates on its axis. French physicist Leon Foucault (“foo-koh”) debuted his pendulum in 1851 at the Paris Observatory, suspending a 62-pound cannon ball by a 200-foot-long piano wire from the dome of the building. A few weeks later he installed his most famous pendulum in the Pantheon, a public building in Paris.

Pendulums on his design became popular and there are now hundreds of them on display all over the world. The one at Western Security Bank, at North Broadway and First Avenue North, besides being the only one in Montana, is one of just a handful in the United States inside a private business. Almost all the rest are in museums, libraries, planetariums and similar venues.

The pendulum in Billings owes its existence to Jim Bennett, who in 1978 moved his First Citizens Bank into what had been the J.J. Newberry department store at 123 N. Broadway. First Citizens had been a block east at First Avenue and North 27th Street, but the city wanted that property for a parking garage.

In the old department store building, Bennett said, there were escalators leading from the ground floor to the selling floor below. But the escalators were out of order and the bank wouldn’t need them anyway.

So, what to do with this big open space in the middle of his new bank? Bennett’s first thought was to cut out a 25-by-25-foot section of the ceiling and install a chandelier. But the cheapest one he could find—and which he didn’t particularly like—would have cost $250,000, what with the need to lower and raise it for cleaning.

Then he thought of the Foucault’s pendulum he had seen as a young man. Bennett was born in 1931 in Havre, when his parents were living on a homestead near Logie, 10 miles southeast of Havre. In 1949, the year Bennett graduated from Chinook High School, he was one of 30 Montana delegates who attended the National 4-H Club Congress in Chicago.

It was his first time out of state, and among the marvels he saw in the metropolis was a Foucault’s pendulum at the Museum of Science and Industry. Almost 30 years later, standing inside his new bank, he thought back to that museum visit.

“I remembered that pendulum,” Bennett said. “It must have impressed me. So I thought, ‘you know, you could put a pendulum in there.’”

The only place in the country that installed Foucault’s pendulums then was the California Academy of Sciences in San Francisco. The academy said it could install one for $8,000. You didn’t have to be a banker to know that sounded like a pretty good deal.

So Bennett had the section of ceiling cut out to accommodate the cable that would hold the pendulum’s bob, or weight. The hollow brass bob weighs 235 pounds and swings on a 40-foot steel cable. The pendulum is kept in motion by means of an electromagnetic device.

Your Last Best News correspondent, aware of his limitations in regard to mathematics and science in general, asked Tom Tollefson, his old friend and for years his editor at the Billings Gazette, to provide an explanation of the pendulum’s operation. He wrote:

“An ordinary pendulum swings a weight attached to a rigid spoke bearing on an axle, as in a grandfather’s clock. It oscillates back and forth in a fixed plane as gravity pulls against the motion imparted to the bob.

“Foucault’s pendulum differs because the weight is suspended by a long wire from a pivot point. So the path of the pendulum bob remains in its ‘absolute’ plane in Newtonian space, and as the Earth rotates beneath the swinging bob, its path appears to move in a circle.

“At the Earth’s poles (yes, there was once a six-story Foucault’s pendulum at the South Pole), a complete revolution would take 24 hours. The period varies with latitude according to math even more complicated than the Montana income tax form.

“What is it for? For show, mostly. It demonstrates vividly what we knew already, that the Earth rotates daily on its roughly north-south axis. The device is not really a scientific instrument or experiment. It is more like a big science fair project that fascinates observers with the majestic sweep of its bob and its slow procession around the compass.”

At the equator, no shift in direction would be apparent. In Billings, the progression rate of the Earth’s rotation is 10.6 degrees an hour. As with many pendulums of this kind, the one in Billings has pins arranged in a circle under it, and as the earth rotates and time elapses, the weight knocks down the pins in succession. (You can see a nifty animated illustration of the pendulum’s movement on Wikipedia.)

Years ago, Bennett said, a bank customer built a clock face in the middle of the circle through which the weight passes. It had a motor that moved the clock face 4.4 degrees an hour, so that the weight showed the correct time as it passed over the clock. (The added 4.4 degrees per hour, combined with the progression rate of 10.6 degrees, made for 15 degrees an hour, or 360 degrees in one day.)

The motor running the clock face no longer works, but the pendulum is still doing its job. Jan Peterson, Western Security’s branch manager, said not that many people come into the bank any more just to see the pendulum, “but for everyone who comes in, it’s definitely a focal point.”

Karen Derheim, a receptionist who has worked in the building for 35 years, the last 16 for Western Security, still keeps handouts with information on the pendulum in her desk, for those who do want to learn more about it.

Bennett, who retired from the banking business in 1994, said that when he first installed the pendulum, he printed brochures and invited science teachers at local schools to bring their students down on field trips to see the marvel. They did, in great numbers.

“My thought was, they couldn’t get through 12 years of school without being in here three or four times, anyway,” Bennett said. “So they would know about the bank with the pendulum, even if they didn’t know the name of the bank.”

It may have grown a little too popular.

“I suppose maybe the parents of some of the kids worked for another bank,” Bennett said, “so other banks put the heat on the school district and made them quit doing it. I was young and foolish then. I let them get away with it.”

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