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Visitors to the Albertus Magnus Science Hall on the California campus of ���ϲ����� will see a large brass sphere, dangling some 25 feet from the ceiling in the building’s lobby. On the floor beneath stands a circle of pegs, which the swinging sphere steadily knocks over, one at a time, at a rate of one every 1 hour, 10 minutes, and 42 seconds.

This marvelous device is called a Foucault Pendulum, named for the French physicist Léon Foucault, who created the first of its kind in 1851 to give simple, direct evidence of the earth’s rotation.  How it works, and what it tells us, is the subject of the above video, featuring ���ϲ����� tutor and alumnus Dr. Gregory L. Froelich (’83).

“In Sophomore Mathematics we ask the question, ‘How do we know the earth in spinning on its axis?’” Dr. Froelich begins. From there, he discusses the design and the motion of the pendulum, referencing material from his September 2021 lecture, Science and Freedom. “It’s not the pendulum twisting about, but the floor under the pendulum,” he concludes. “In fact, if the floor, then the whole building; and if the whole building, the whole earth.”