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 Panthéon 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.

The Ozone Layer

     In the 1970s scientists of the British Antarctic Survey observed a drop in atmospheric ozone over the Antarctic. A hole in the ozone layer was detected in the 1980s. This permits damaging ultraviolet radiation, which may cause skin cancers, eye damage, immune system damage and damage to the ecosystem.
     The ozone hole reached it maximum size in 2000, 11 million square miles, three times the size of the United States. International agreements regulating the release of ozone destroying chemicals into the atmosphere has slowed the damage to the ozone layer.
     Also in 2000 Brazil issued this stamp to mark the "International Day for the Preservation of the Ozone Layer."