X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated

Now You See It, Now You Don't - The Foucault Pendulum at the National Museum of American History

In honor of the anniversary of the discovery of x-rays, a look inside the Foucault pendulum that used to live at the National Museum of American History.
November 8, 2018, by Mitch Toda

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Black and white x-ray of the Foucault pendulum bob at the National Museum of American History.

X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Black and white photo of a crowd of people in a museum watching a Foucault pendulum knock over pegs.

A crowd watches Foucault's Pendulum in the Museum of History and Technology, now known as the National Museum of American History, November 6, 1967. Image no. OPA-1109-04. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated, Smithsonian Institution Archives.

Black and white x-ray of the Foucault pendulum bob at the National Museum of American History.

X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Cover of an educational guide on Foucault pendulums.

Cover of Foucault pendulum educational guide, c. 1970s. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Text and diagrams explaining how a Foucault pendulum works.

Foucault pendulum educational guide - Explanation of how it works. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Black and white x-ray of the Foucault pendulum bob at the National Museum of American History.

X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Black and white x-ray of the Foucault pendulum bob at the National Museum of American History.

X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Color photo of a Foucault pendulum in motion.

Foucault pendulum, National Museum of American History, 1989. Photo by Dane Penland. Image no. 89-8589-26. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Black and white x-ray of the Foucault pendulum bob at the National Museum of American History.

X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Wooden platform being constructed inside the National Museum of American History.

Preparing and protecting the Foucault pendulum at the National Museum of American History for the inaugural ball of President Richard M. Nixon, January 18, 1973. Image no. 73-494-07A. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Black and white x-ray of the Foucault pendulum bob at the National Museum of American History.

X-ray of the Foucault pendulum bob, National Museum of American History. Accession 17-183: National Museum of American History, Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated. Smithsonian Institution Archives.

Today marks the anniversary of the discovery of x-rays by Wilhelm Conrad Roentgen, who was awarded the first Nobel Prize in Physics in 1901 for his discovery. The Smithsonian is no stranger to x-rays and related objects in its collections. From fishes at the National Museum of Natural History to x-ray tubes and equipment at the National Museum of American History, we have quite a breadth of materials related to x-rays. 

Pendulum Hall in NMHT

Last year, the Archives acquired a collection of materials from the National Museum of American History, which included x-ray images of the Foucault pendulum that used to be in the center of the museum along with the Star Spangled Banner. Its stay at the museum started in 1964 when the museum opened. It had a brief hiatus in 1987 when then pendulum was moved from the first floor to the second floor, and then finally was taken down in 1998 to make room for the Star Spangled Banner Preservation Project.

Museum of History and Technology Exhibit

NMAH's pendulum was made by the California Academy of Sciences and was suspended four stories from the ceiling of the museum. The pendulum demonstrated that the earth rotates counterclockwise on its axis by observing the motion of the pendulum. It consisted of a thin, flexible wire (54 feet long) with a heavy weight, the bob (made of hollow brass, nearly fifteen inches in diameter, and weighing about 240 pounds), attached to the end. The museum's pendulum was suspended from a tapered support that allowed it to bend in a slightly different direction on each swing which took 9.3 seconds.

Foucault Pendulum and the Star-Spangled Banner

Related Resources

Related Collections

  • Accession 17-183: National Museum of American History. Division of the History of Technology, Exhibition Records, 1964-1978, 1982, 1987-1989, 1995, 1998, undated, Smithsonian Institution Archives

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