Jean-Bernard-Leon Foucault was a French physicist who is considered one of the most versatile experimentalists of the nineteenth century. He is well known for his experiments in optics and mechanics and was involved in the development of a method to measure the speed of light with extreme accuracy. Foucault is most often remembered for proving, with the use of a pendulum, that the Earth rotates on its axis.On September 18, 1819 Foucault was born in Paris, France, the son of a publisher. His early education was received at home and he showed youthful promise in mechanics. After obtaining his bachelor of arts degree, Foucault entered medical school but soon abandoned the program. Instead, he began working for Alfred Donne, making preparations for a university medical microscopy course. Since his elementary mathematical and scientific training had been inadequate for his interests, Foucault supplemented it as he became involved with invention and experiment.Foucault met the French physicist Armand Fizeau in 1839 and the pair worked in close collaboration for almost a decade. Together they took the first detailed pictures of the sun's surface and developed a more precise way to measure the speed of light in 1849. Foucault proved independently that the speed of light in air is greater than it is in water. His other contributions to the field of optics included a method of measuring the curvature of telescope mirrors, an improved technique to silver astronomical mirrors, a method of testing telescope mirrors for surface defects, and the invention of a polarizing prism to orient and manipulate polarized light.Leon Foucault bounced light from a rotating mirror back to a stationary mirror. The light from the rotating mirror bounced back at an angle slightly different from the angle it hit the mirror with - because the mirror was rotating. By measuring this angle it was possible to measure the speed of the light.Foucault continually increased the accuracy of this method over the next 50 years. His final measurement in 1926 determined that light travelled at 299,796 Km/s.
