Jean-Bernard-Leon FoucaultThe speed of light measured by using a rotating mirror During the 19th century, Foucault was considered one of the most brilliant experimentalists. He developed the method of measuring the speed of light with tight accuracy. In 1839, Foucault worked closely with Armand Fizeau, another French physicist for a decade. During the year 1849, they took the first detailed photos of the sun’s surface and made a precise way to measure the speed of light. By himself, Foucault established that the speed of light in the air is more greater than it is in water. Foucault conducted an experiemtn by using a rotating mirror. He observed that light from a the rotating mirror bounced back to a stationary mirror. The light from the rotating mirror hit back at a different angle than the angle that it hit the mirror with. The reason for this was because the mirror was rotating. Foucault figured that if he could measure the angle, it was possible to measure the speed of light. Here is a diagram of Foucault's Spinning Mirror Device |
