French Physicist. He invented the Foucault Pendulum which provided experimental proof that Earth rotates on its axis. He also introduced and helped develop a technique of measuring the absolute speed of light with extreme accuracy. He was educated for the medical profession, but his interests turned to experimental physics. By 1850, he had established that light travels slower in water than in air. In the same year, he measured the speed of light, finding a value that is within one percent of the true figure. In 1851, by interpreting the motion of a heavy iron ball swinging from a wire 67 meters (220 feet) long, he proved that Earth rotates about its axis. The Foucault Pendulum always swings in the same vertical plane, but on a rotating Earth, this vertical plane slowly changes, at a rate and direction dependent on the geographic latitude of the pendulum. For this demonstration and a similar one using a gyroscope, he received the Copley Medal of the Royal Society of London in 1855 and was made physical assistant at the Imperial Observatory, Paris. He also discovered the existence of eddy currents, or Foucault Currents, in a copper disk moving in a strong magnetic field, constructed an improved mirror for the reflecting telescope, and in 1859, he invented a simple but extremely accurate method of testing telescope mirrors for surface defects.

French Physicist. He invented the Foucault Pendulum which provided experimental proof that Earth rotates on its axis. He also introduced and helped develop a technique of measuring the absolute speed of light with extreme accuracy. He was educated for the medical profession, but his interests turned to experimental physics. By 1850, he had established that light travels slower in water than in air. In the same year, he measured the speed of light, finding a value that is within one percent of the true figure. In 1851, by interpreting the motion of a heavy iron ball swinging from a wire 67 meters (220 feet) long, he proved that Earth rotates about its axis. The Foucault Pendulum always swings in the same vertical plane, but on a rotating Earth, this vertical plane slowly changes, at a rate and direction dependent on the geographic latitude of the pendulum. For this demonstration and a similar one using a gyroscope, he received the Copley Medal of the Royal Society of London in 1855 and was made physical assistant at the Imperial Observatory, Paris. He also discovered the existence of eddy currents, or Foucault Currents, in a copper disk moving in a strong magnetic field, constructed an improved mirror for the reflecting telescope, and in 1859, he invented a simple but extremely accurate method of testing telescope mirrors for surface defects.

Bio by: Glendora