The year1809 inscience andtechnology involved some significant events, listed below.

• Carl Friedrich Gauss publishesTheoria motus corporum coelestium in sectionibus conicis solem ambientum inHamburg, introducing theGaussian gravitational constant and containing an influential treatment of theleast squares method.^[1]
• S. D. Poisson publishesSur les inégalités séculaires des moyens mouvements des planètes andSur la variation des constantes arbitraires dans les questions de mécanique in theJournal of theÉcole Polytechnique, extendingLagrange's theory ofplanetary orbits.

• Jean-Baptiste Lamarck publishesPhilosophie Zoologique, outlining his theory ofevolution.
• Johann Heinrich Friedrich Link first describesPenicillium.^[2]

• William Maclure publishes the firstgeological map of theUnited States with accompanying memoir.^[1][3]

• Louis Poinsot describes the two remainingKepler-Poinsot polyhedra.

• December 25 –AmericanphysicianEphraim McDowell performs the world's firstovariotomy, the removal of anovarian tumor.^[4]
• Philippe Pinel publishes accounts of what would later be regarded asschizophrenia.^[5]

• February 11 –Robert Fultonpatents thesteamboat in theUnited States.^[6][7]
• May 5 –Mary Kies becomes one of the first women granted a U.S. patent, for a technique of weavingstraw hats withsilk andthread.^[8]
• Samuel Thomas von Sömmerring invents a watervoltameterelectrical telegraph.^[1]
• William Hyde Wollaston invents the reflectinggoniometer.

• Copley Medal:Edward Troughton^[9]

• January 4 –Louis Braille (died1852), Frenchinventor.
• January 6 –Marie Durocher (died1893), Brazilian physician.
• February 12 –Charles Darwin (died1882), Englishnaturalist.
• February 15 –Cyrus McCormick (died1884), American inventor.
• February 21 –Carl Ernst Bock (died1874), Germanphysician andanatomist.
• April 7 –James Glaisher (died1903), Englishmeteorologist and balloonist.
• April 15 –Hermann Grassmann (died1877), Germanmathematician.
• April 20 –James David Forbes (died1868), Scottish physicist, glaciologist and seismologist.
• August 29 –Oliver Wendell Holmes Sr. (died1894), American physician and writer.
• November 22 –Bénédict Morel (died1873), Frenchpsychiatrist.
• Date unknown –William Lobb (died1864), English plant collector.

• May 17 –Leopold Auenbrugger (born1722), Austrian physician.
• August 18 –Matthew Boulton (born1728), English mechanical engineer.
• October 11 –Meriwether Lewis (born1774), American explorer.
• December 16 –Antoine François, comte de Fourcroy (born1755), French chemist.
• December 29 –Thomas Barker (born 1722), English meteorologist.

• 1809 in science
• 19th century in science
• 1800s in science

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