Foucault , Jean Bernard Léon
(1819–1868) French physicist
Foucault, the son of a Parisian bookseller, originally intended to study medicine, but transferred his interest to physical science. In 1855 he became a physicist at the Paris Observatory.
His main work was on measurements of the speed of light. He helped Armand Fizeau in his toothed-wheel experiment and, in 1850, took over D.F.J. Arago's experiments on comparing the speed of light in air with that in water. The experiment was important for distinguishing between the wave and particle theories of light: the wave theory predicted that light should travel faster in air than in water; the particle theory predicted the opposite. In 1850, Foucault showed that the wave-theory prediction was correct. In 1862 he obtained the first accurate value for the speed of light using a rotating-mirror apparatus.
Foucault also worked on other topics. Thus he noted (1849) that a bright yellow line in the spectrum of sodium corresponded to a dark line in the Fraunhofer spectrum of the sun, although he failed to follow this up.
His most famous experiments began in 1850 and involved pendulums. While trying to construct an accurate timing device for his work on light, he noticed that a pendulum remained swinging in the same plane when he rotated the apparatus. He then used a pendulum to demonstrate the rotation of the Earth. Over a long period of time the plane in which a pendulum is swinging will appear to rotate. In fact the pendulum swings in a fixed plane relative to the fixed stars, and the Earth rotates ‘underneath’ it.
At the Earth's poles, the plane of the pendulum will make one full rotation every 24 hours; this period increases as the equator is approached. Foucault derived an equation relating the time of rotation to the latitude. He also gave public exhibitions of the effect, including one in which he suspended an iron ball of 28 kilograms (62 lbs) by steel wire 67 meters (222 ft) long from the dome of the Panthéon in Paris. Foucault also invented the gyroscope.

Scientists. . 2011.

Look at other dictionaries:

  • Foucault, Jean Bernard Léon — Fou·cault (fo͞o kōʹ), Jean Bernard Léon. 1819 1868. French physicist who estimated the speed of light and determined that it travels more slowly in water than in air (1850). He also employed a pendulum to prove the rotation of the earth (1851)… …   Universalium

  • Foucault, Jean (-Bernard-Léon) — (18 sep. 1819, París, Francia–11 feb. 1868, París). Físico francés. Aunque estudió medicina, sus intereses estaban en la física. En 1850 midió la velocidad de la luz con gran precisión. Inventó el llamado péndulo de Foucault y lo usó como prueba… …   Enciclopedia Universal

  • Foucault, Jean (-Bernard-Léon) — born Sept. 18, 1819, Paris, France died Feb. 11, 1868, Paris French physicist. Though educated in medicine, his interests lay in physics. In 1850 he measured the speed of light with extreme accuracy. He invented the Foucault pendulum and used it… …   Universalium

  • Jean Bernard Leon Foucault — Jean Bernard Léon Foucault (* 18. September 1819 in Paris; † 11. Februar 1868 ebenda) war ein französischer Physiker. Inhaltsverzeichnis 1 Leben 2 Wirkung 3 Weblinks 4 Quellen …   Deutsch Wikipedia

  • Jean Bernard Leon Foucault — Léon Foucault Pour les articles homonymes, voir Foucault. Jean Bernard Léon Foucault, né à Paris le 18 septembre 1819 et mort à Paris le 11 février 1868, était un physicien et astronome français. Connu principalement pour son… …   Wikipédia en Français

  • Jean Bernard Léon Foucault — Léon Foucault Pour les articles homonymes, voir Foucault. Jean Bernard Léon Foucault, né à Paris le 18 septembre 1819 et mort à Paris le 11 février 1868, était un physicien et astronome français. Connu principalement pour son… …   Wikipédia en Français

  • Jean Bernard Léon Foucault — (* 18. September 1819 in Paris; † 11. Februar 1868 ebenda) war ein französischer Physiker. Inhaltsverzeichnis 1 Leben 2 Wirkung 3 Weblinks …   Deutsch Wikipedia

  • Jean Bernard Leon Foucault — noun French physicist who determined the speed of light and showed that it travels slower in water than in air; invented the Foucault pendulum and the gyroscope (1819 1868) • Syn: ↑Foucault • Instance Hypernyms: ↑physicist …   Useful english dictionary

  • Jean Bernard Leon Foucault — gyroscope …   Inventors, Inventions

  • Jean Bernard Foucault — Jean Bernard Léon Foucault (* 18. September 1819 in Paris; † 11. Februar 1868 ebenda) war ein französischer Physiker. Inhaltsverzeichnis 1 Leben 2 Wirkung 3 Weblinks 4 Quellen …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”