Hippolyte Fizeau

{{Infobox scientist

| honorific_suffix = {{post-nominals|country=GBR|size=100%|ForMemRS}}

| image = Armand Hippolyte Louis Fizeau by Eugène Pirou - Original.jpg

| caption = Photograph of Fizeau by Eugène Pirou, 1883

| birth_name = Armand Hippolyte Louis Fizeau

| birth_date = {{birth date|df=y|1819|9|23}}

| birth_place = Paris, Kingdom of France

| death_date = {{death date and age|df=y|1896|9|18|1819|9|23}}

| death_place = Venteuil, French Third Republic

| fields = Physics

| work_institutions =

| known_for = {{plainlist|

Discovering the Doppler redshift (1848)
Measuring the speed of light in air (1848–1849)
Performing the Fizeau experiment (1851)
Improving the induction coil (1853)

}}

| awards = Rumford Medal (1866)
ForMemRS (1875)

}}

Armand Hippolyte Louis Fizeau ({{IPA|fr|ipɔlit fizo|lang}}; 23 September 1819 – 18 September 1896) was a French physicist who, in 1849, measured the speed of light 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.{{cite book |title=The Biographical Encyclopedia of Astronomers |last=Hockey |first=Thomas |year=2009 |publisher=Springer Publishing |isbn=978-0-387-31022-0 |access-date=August 22, 2012 |url=http://www.springerreference.com/docs/html/chapterdbid/58464.html}} He married into the de Jussieu botanical family. His earliest work was concerned with improvements in photographic processes.{{cite journal |editor1-last=Solbert |editor1-first=Oscar N. |editor2-last=Newhall |editor2-first=Beaumont |editor3-last=Card |editor3-first=James g. |title=Hippolyte-Louis Fizeau (1819–1896) |journal=Image, Journal of Photography of George Eastman House |date=May 1952 |volume=1 |issue=5 |pages=3–4 |url=http://image.eastmanhouse.org/files/GEH_1952_01_05.pdf |access-date=22 June 2014 |publisher=International Museum of Photography at George Eastman House Inc. |location=Rochester, N.Y. |url-status=dead |archive-url=https://web.archive.org/web/20140714144808/http://image.eastmanhouse.org/files/GEH_1952_01_05.pdf |archive-date=14 July 2014 }} Following suggestions by François Arago, Léon Foucault and Fizeau collaborated in a series of investigations on the interference of light and heat.{{EB1911|inline=y|wstitle=Fizeau, Armand Hippolyte Louis|volume=10|page=452}} In 1848, he predicted the redshifting of electromagnetic waves.{{cite book | title=The Timetables of Science | last=Hellemans | author2=Bryan Bunch | publisher=Simon and Schuster | location=New York City | year=1988 | isbn=0-671-62130-0 | pages=[https://archive.org/details/timetablesofscie00hell_0/page/317 317] | first=Alexander | url-access=registration | url=https://archive.org/details/timetablesofscie00hell_0/page/317 }}

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.{{cite web |title=Fizeau's experiment: The original paper |url=https://skullsinthestars.com/2008/03/31/fizeaus-experiment-the-original-paper/ |website=Skulls in the Stars |access-date=9 March 2023 |language=en |date=1 April 2008}} This gives a result of

{{math|2 x 8633m x 25.2 x 720/s {{=}} 313,274,304 m/s}}, 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.){{cite book |chapter=Experiments of MM. Fizeau and Gounelle |title=Maxwell's Theory and Wireless Telegraphy: Part 1 |last1=Poincaré |first1=H. |location=New York |publisher=McGraw Publishing Co. |year=1904 |pages=52–55 |chapter-url=https://books.google.com/books?id=BvVUAAAAMAAJ&pg=PA52}} Fizeau made the first suggestion in 1864 that the "speed of a light wave be used as a length standard".Physics part 1 Resnick/Halliday p. 5.

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.{{cite book|last1=Tobin|first1=William John|title=The Life and Science of Leon Foucault: The Man Who Proved the Earth Rotates|date=2003|publisher=Cambridge University Press|isbn=9780521808552 |url=https://archive.org/details/lifescienceofleo0000tobi |access-date=10 March 2023 }}{{rp|129}}

Fizeau was involved in the discovery of the Doppler effect,{{cite journal |last=Houdas |first=Y. |date=April 1991 |title=Doppler, Buys-Ballot, Fizeau. Historical note on the discovery of the Doppler's effect |journal=Annales de cardiologie et d'angéiologie |volume=40 |issue=4 |pages=209–13 | pmid = 2053764 | language =fr}} 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 crystals. 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.{{cite web|url=https://www.toureiffel.paris/en/news/130-years/whose-are-72-names-inscribed-eiffel-tower-and-why-are-they-there|title=Whose are the 72 names inscribed on the Eiffel Tower and why are they there|last=Lemoine|first=Bertrand|date=2020-06-18|access-date=2023-05-10|url-status=live|archive-url=https://web.archive.org/web/20230129025127/https://www.toureiffel.paris/en/news/130-years/whose-are-72-names-inscribed-eiffel-tower-and-why-are-they-there|archive-date=2023-01-29}}

The crater Fizeau on the far side of the Moon is named after him.{{Cite web |url=https://planetarynames.wr.usgs.gov/Feature/1968 |title=Fizeau on Moon |website=Gazetteer of Planetary Nomenclature |publisher=United States Geological Survey |access-date=2018-09-21 |df=dmy-all}}