Jean Foucault

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Jean Foucault

In 1850, Jean Foucault and Fizeau conducted an experiment using the Foucault-Fizeau apparatus to measure the speed of light. However, they eventually parted ways and conducted experiments on their own. Foucault used rotating mirror devices to perform relative measures of the speed of light in air versus water. The device works by having light reflect off of a rotating mirror forming an image, which is then reflected again. As the rotating mirror will have moved slightly in the time it takes for the light to bounce off the determined points, the light will be deflected away from the original source, thus creating an angle. Surprisingly, Foucault was able to measure the speed of light with incredible accuracy. His figure for the speed of light (298000 km/s) was within 0.6% of the modern value.

This is a stationary version of Foucault's spinning mirror method. In the bottom left corner you can see how it actually works.

The apparatus above is a diagram of the Foucault-Fizeau apparatus that was initially used to determine the speed of light before the two men decided to part ways.

Shorter video, gives a brief explanation as to how Foucault's method worked. (Explained in a detailed manner in other video)

French physicist, Jean Bernard. Most known for his mirror method on discovering the speed of light.

This image shows Foucault's Spinning Mirror Device. It was used to demonstrate the speed of light. The video below will help explain how.

Jean FoucaultAlexis & Eva


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