Armand Hippolyte Louis Fizeau (; 23 September 1819 – 18 September 1896) was a French
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...
who, in 1849, measured the
speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...
to within 5% accuracy. In 1851, he measured the speed of light in moving water in an experiment known as the
Fizeau experiment.
Biography
Fizeau was born in Paris to Louis and Beatrice Fizeau. He married into the
de Jussieu botanical family. His earliest work was concerned with improvements in photographic processes. Following suggestions by
François Arago,
Léon Foucault and Fizeau collaborated in a series of investigations on the
interference of light and heat.
In 1848, he predicted the
redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...
ing of
electromagnetic wave
In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ...
s.
In 1849, Fizeau calculated a value for the speed of light to a better precision than the previous value determined by
Ole Rømer in 1676. He used a beam of light reflected from a mirror 8633 meters away. The beam passed through the gaps between the teeth of a rapidly rotating wheel with 720 teeth. The speed of the wheel was increased until, at 12.6 rotations per second, the returning light hit the next tooth and could not be seen. At 25.2 rotations per second, the light was again visible.
This gives a result of
, which is within 5% of the correct value (
299,792,458 meters per second). (See
Fizeau's measurement of the speed of light in air.) Fizeau made the first suggestion in 1864 that the "speed of a light wave be used as a length standard".
In 1850 he measured the
relative speeds of light in air and water, using a rotating mirror, however Foucault independently achieved the same result seven weeks earlier.
Fizeau was involved in the discovery of the
Doppler effect, which is known in French as the Doppler–Fizeau effect.
In 1853, Fizeau described the use of a
capacitor (sometimes termed a "condenser") as a means to increase the efficiency of the
induction coil. Later, he studied the
thermal expansion of solids and applied the phenomenon of interference of light to the measurement of the dilatations of
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s. He became a member of the
Académie des Sciences in 1860 and a member of the
Bureau des Longitudes in 1878. He died in France at
Venteuil on 18 September 1896.
"Fizeau" is one of the
72 names inscribed on the frieze below the first platform of the Eiffel Tower, all of whom were French scientists, mathematicians, engineers, or industrialists from the hundred years before the tower's public opening for the
1889 World's Fair. Of the 72, Fizeau is the only one who was still alive when the tower was opened.
The crater
Fizeau on the
far side of the Moon is named after him.
See also
*
Daguerreotype
*
Michelson stellar interferometer
*
Optical chopper
*
Léon Foucault
References
External links
*
*
Open Library
{{DEFAULTSORT:Fizeau, Hippolyte
1819 births
1896 deaths
Scientists from Paris
French physicists
French optical physicists
Foreign members of the Royal Society
Members of the French Academy of Sciences
Members of the Royal Society of Sciences in Uppsala