Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from F-J

Fizeau, Armand Hippolyte Louis

light wheel speed using

[feezoh] (1819–96) French physicist: determined the velocity of light experimentally.

Born into a wealthy family, Fizeau turned from studying medicine to research in optics. With he improved the early photographic process introduced by and obtained the first detailed pictures of the Sun (1845).

Fizeau made the first accurate determination of the speed of light (1849). In an experiment using an 8 km light path between the hilltops of Suresnes and Montmartre, he sent a light-beam through a rotating toothed wheel and reflected it from the far hilltop so that it returned through the wheel. At a certain speed of the wheel the return signal was blocked by a tooth of the wheel, enabling the speed of light to be calculated.

The following year, Fizeau, working with L F C Brequet (1804–83), showed that light travels more slowly in water than in air: Foucault simultaneously made the same discovery. This was strong evidence against particle theory of light and for wave theory. In 1851 Fizeau measured the effect on light when it is passed through a moving medium (water); the result was in excellent agreement with Fresnel’s prediction. Fizeau was the first to apply results on moving wave sources and observers to light as well as sound. Other experiments by Fizeau included using the wavelength of light for measurement of length by interferometry and using interference to find the apparent diameter of stars.

Many honours were given to Fizeau for his work, including membership of the French Académie des Sciences (1860) and foreign membership of the Royal Society of London (1875).

Flagellation [next] [back] Five Senses

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

about 6 years ago

Do you know the wavelenght used by Fizeau in his expeiment? Did it correspond to the center of the Na epectrum with n=1.33 for water?