Hippolyte Fizeau

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Hippolyte Fizeau.

Armand Hippolyte Louis Fizeau (born September 23, 1819 in Paris , † September 18, 1896 in Venteuil near Épernay ) was a French physicist .

Fizeau worked as a private scholar in physics and astronomy . In 1860 he was accepted into the Académie des Sciences , in 1878 he was elected President of the Bureau des Longitudes .

Under the influence of François Arago , Fizeau initially turned to astronomical problems. Together with Léon Foucault , Fizeau produced the first image of the sun in 1845, with which he founded astronomical photography . In addition, both investigated the infrared radiation of the sun and the interference phenomena of light. The Fizeau stripes (interference phenomena on wedge-shaped leaves) are evidence of this work . Independently of Christian Doppler (1842), Fizeau predicted in 1848 the Doppler shift of the frequency of light and thus of spectral lines .

In 1849 Fizeau took measurements of the speed of light in various media. His first investigation was the speed of light in air, for which he refined a method devised by Galileo Galilei . With a rotating gear and with the help of two telescopes, he was able to calculate the speed from the speed of rotation of the wheel and the distance covered by light ( gear method ). The value found, which was five percent too high, was later corrected by Foucault. Also in 1849 Fizeau calculated the speed of light in still water using the method of mirror rotation, followed in 1851 by measurements in moving water (" Fizeau experiment "). Based on the measurement results, Fizeau was able to show that the speed of light in water is lower than in air. The dependence of the speed of light on the direction of flow of the water could not be reconciled with the law of addition of the speeds of classical mechanics, which is why Albert Einstein 's measurements were later evaluated as experimentum crucis (decisive experiment) for the special theory of relativity .

Fizeau also worked in the field of thermodynamics , where he constructed an interference dilatometer for measuring the thermal expansion of solid bodies . In 1850 he and Eugène Gounelle (1821–1864) measured the speed at which electricity spreads in conductors. In 1853 he described the installation of a capacitor to increase the efficiency of induction . He then studied the thermal expansion of solids and applied the phenomenon of light interference to measure the expansion of crystals.

He and 71 other scientists are immortalized by name on the Eiffel Tower and at the time of inauguration was one of two who were still alive. See: The 72 names on the Eiffel Tower .

In 1863 he was accepted as a corresponding member of the Royal Prussian Academy of Sciences . In 1875 he was elected a foreign member of the Royal Society . In 1892 he became an Honorary Fellow of the Royal Society of Edinburgh . In 1866 he received the Rumford Medal from the Royal Society. In 1970 the lunar crater Fizeau was named after him.


  1. ^ Obituary for Gounelle in Annales télégraphiques , Volume 7, p. 92
  2. Historical Academy Members : Armand Hippolyte Louis Fizeau. Berlin-Brandenburg Academy of Sciences, accessed on December 5, 2019 .
  3. ^ Fellows Directory. Biographical Index: Former RSE Fellows 1783–2002. Royal Society of Edinburgh, accessed December 5, 2019 .
  4. ^ Hippolyte Fizeau in the Gazetteer of Planetary Nomenclature of the IAU (WGPSN) / USGS

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