The Impact of the Foucault Pendulum

A part of the Houston Museum of Natural Science (HMNS) since 1991, Joel A. Bartsch held responsibilities as curator and director of earth sciences before taking his current position as president and CEO. Joel Bartsch’s current duties include conceptualizing museum expansion projects and attracting public attention with modern and compelling exhibits.

One of the most interesting fixtures at HMNS is the Herzstein Foucault Pendulum, which is based on a design that was first exhibited at the 1851 World’s Fair in Paris.

The impact of this groundbreaking pendulum, which appears to change direction throughout the day, was profound. While the pendulum appears to change direction as it swings throughout the day, it is actually the Earth rotating underneath the pendulum.

At the World’s Fair in 1851, the pendulum’s inventor, Leon Foucault, suspended a 61-pound brass bob on a 220-foot cable from the dome of the Pantheon building in Paris. The pendulum’s continuous, predictably changing pattern proved that the earth was spherical and turning on an axis.

Soon, pendulums based on Foucault’s calculations were built in the United States. One of the most remarkable examples can be found at the Smithsonian Institution, where it is housed in the Museum of History and Technology, built specifically to accommodate the massive pendulum.

The Herzstein Foucault Pendulum swings on a 60-foot-long cable, has a period lasting seven seconds, and derives the energy needed to overcome friction and wind resistance for the perpetual swinging from a magnet that surrounds the top of the cable.