Léon Foucault

Scientist who demonstrated Earth's rotation and advanced optical measurement

Jean Bernard Léon Foucault transformed our understanding of physics through ingenious experimental demonstrations. His 1851 Foucault pendulum provided the first simple proof of Earth's rotation, visible to the general public.

The pendulum experiment showed that its plane of oscillation rotates relative to Earth's surface. At latitude 30°, the pendulum completes a full rotation every 48 hours. This demonstration made celestial mechanics tangible, replacing abstract mathematical proofs with observable reality.

Foucault also made crucial advancements in light velocity measurement. His 1862 determination of light speed as 298,000 km/s (within 0.6% of modern value) using rotating mirrors remained the most accurate measurement for decades.

In optics, he developed the Foucault knife-edge test for telescope mirror quality, still used in astronomical instrument manufacturing. His 1858 invention of the gyroscope later became crucial for navigation systems.

The Panthéon's Foucault pendulum continues to educate visitors about Earth's rotation. His work exemplifies how elegant experiments can advance public understanding of complex scientific principles.