Foucault’s Pendulum ~ 1851

     In the background of the stamp is an silhouette map of France the homeland of Jean Foucault (1819- 1868). Foucault (pronounced "Foo-Koh") was born on September 19, 1819. He studied medicine, but changed to the physical sciences at the Paris Observatory. Foucault's life is marked by many distinguishing achievements. He was the first scientist to photograph the sun. He was able to measure the speed of light in a laboratory using a system of rotating mirrors. He proved that humans have binocular vision, with the brain combining images from the two eyes into a single image. He is also credited with improvements on mirrors, lenses, prisms, arc lamps, telescopes, and gyroscopes. He died in 1868.
     In 1851 Jean Foucault hung a 61 pound ball on a 200 foot cable and started it swinging in the Pantheon in Paris. A pin on the bottom of the ball traced the path of the swinging ball in wet sand. In 24 hours the path moved 270°. Since a swinging pendulum does not change its direction the change is attributed to the movement of the environment, specifically the building in which the pendulum was hung, thus demonstrating the rotation of the earth.
     If the pendulum were hung at the North Pole it would seem to rotate 360° in 24 hours. If it were hung at the equator it would not change at all. The formula for the apparent rotation is n=360sinF. Since Paris is about 48.6°, the apparent rotation was about 270° in 24 hours.
     The stamp was issued to observe the bicentennial of the National Conservatory of Arts and Crafts in 1994.