1843 in science

• March 11–14 – Eta Carinae flares to become the second brightest star.
• February 5–April 19 – "Great March Comet" observed.
• December 21 – The first total solar eclipse of Saros 139 occurs over southern Asia.
• Heinrich Schwabe reports a periodic change in the number of sunspots: they wax and wane in number according to a ten-year cycle.

• Jean-Baptiste Dumas names lactose.Dumas (1843). Traité de Chimie, Appliquée aux Arts. 6 Paris: Bechet Jeune. [https://books.google.com/books?id=zQTyoAqqQzYC&pg=PA293 p. 293.]
• Carl Mosander discovers the chemical elements Terbium and Erbium.{{cite web |title=Carl Gustav Mosander - Oxford Reference |url=https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100211520 |website=www.oxfordreference.com |access-date=16 February 2020 |language=en }}
• John J. Waterston produces an account of the kinetic theory of gases.{{cite book|title=Thoughts on the Mental Functions; being an attempt to treat metaphysics as a branch of the physiology of the nervous system|location=Edinburgh|publisher=Oliver & Boyd|year=1843}}
• Alfred Bird produces single-acting baking powder.{{cite news|first=Matthew|last=Cannon|url=https://www.birminghammail.co.uk/incoming/alfred-bird-egg-free-custard-inventor-8040314|title=Alfred Bird: Egg-free custard inventor and chemist|work=Birmingham Mail|date=2014-11-03|accessdate=2018-02-25}}

• September – Ada Lovelace translates and expands Menabrea’s notes on Charles Babbage's analytical engine, including an algorithm for calculating a sequence of Bernoulli numbers, regarded as the world's first computer program.{{cite journal|first1=John|last1=Fuegi|first2=Jo|last2=Francis|s2cid=40077111|title=Lovelace & Babbage and the creation of the 1843 'notes'|journal=IEEE Annals of the History of Computing|volume=25|issue=4|pages=16–26|doi=10.1109/MAHC.2003.1253887|date=October–December 2003}}{{cite web|url=http://cs-www.cs.yale.edu/homes/tap/Files/ada-bio.html|title=Ada Byron, Lady Lovelace|access-date=2010-07-11|archive-url=https://web.archive.org/web/20100721013509/http://cs-www.cs.yale.edu/homes/tap/Files/ada-bio.html|archive-date=21 July 2010|url-status=live}}{{cite journal|last=Menabrea|first=L. F.|author-link=Luigi Federico Menabrea|year=1843|title=Sketch of the Analytical Engine Invented by Charles Babbage|journal=Scientific Memoirs|volume=3|url=http://www.fourmilab.ch/babbage/sketch.html|access-date=2010-10-01|archive-url=https://web.archive.org/web/20100913042032/http://www.fourmilab.ch/babbage/sketch.html|archive-date=13 September 2010|url-status=live}}
• October 16 – William Rowan Hamilton discovers the calculus of quaternions and deduces that they are non-commutative.{{cite web|title=William Rowan Hamilton Plaque|url=https://www.geograph.org.uk/photo/347941|work=Geograph|year=2007|access-date=2011-03-08}}
• Arthur Cayley and James Joseph Sylvester found the algebraic invariant theory.
• John T. Graves discovers the octonions.
• Pierre-Alphonse Laurent discovers and presents the Laurent expansion theorem.

• James Prescott Joule experimentally finds the mechanical equivalent of heat.{{cite journal|title=On the Mechanical Equivalent of Heat|last=Joule|first=J. P.|journal=Abstracts of the Papers Communicated to the Royal Society of London|year=1843|volume=5|page=839|doi=10.1098/rspl.1843.0196|doi-access=free}}
• Ohm's acoustic law is proposed by German physicist Georg Ohm.

• April–May – English surgeon Benjamin Brodie extracts a coin lodged in the bronchus of engineer Isambard Kingdom Brunel using novel methods.Brodie, Benjamin. "An account of a case in which a foreign body was lodged in the right bronchus." Paper to Royal Medical & Chirurgical Society 27 June 1843.
• British surgeon James Braid publishes Neurypnology: or the Rationale of Nervous Sleep, a key text in the history of hypnotism.
• Oliver Wendell Holmes Sr., argues that puerperal fever is spread by lack of hygiene in physicians."The Contagiousness of puerperal fever". New England Quarterly Journal of Medicine and Surgery.

• March 25 – Completion of the Thames Tunnel, the first bored underwater tunnel in the world (engineer: Marc Isambard Brunel).{{cite book|first=Denis|last=Smith|title=London and the Thames Valley|page=17|location=London|publisher=Thomas Telford|year=2001|isbn=978-0-7277-2876-0}}
• July 19 – Launch of {{SS|Great Britain}}, the first iron-hulled, propeller-driven ship to cross the Atlantic Ocean (designer: Isambard Kingdom Brunel).{{cite news|title=Royal Visit|work=The Bristol Mirror|pages=1–2|date=20 July 1843}}
• November 21 – Thomas Hancock patents the vulcanisation of rubber using sulphur in the United Kingdom
• The steam powered rotary printing press is invented by Richard March Hoe in the United States.{{cite book|last=Meggs|first=Philip B.|author-link=Philip B. Meggs|title=A History of Graphic Design|publisher=Wiley|year=1998|edition=3rd|page=147|isbn=978-0-471-29198-5}} It receives {{US Patent|5199}} in 1847 and is placed in commercial use the same year.
• Robert Stirling and his brother James convert a steam engine at a Dundee factory to operate as a Stirling engine.
• The first public telegraph line in the United Kingdom is laid between Paddington and Slough.
• Approximate date – Euphonium invented.

• October – Anna Atkins begins publication of Photographs of British Algae: Cyanotype Impressions, a collection of contact printed cyanotype photograms of algae which forms the first book illustrated with photographic images.{{cite book|last1=Parr|first1=Martin|first2=Gerry|last2=Badger|title=The Photobook: a history, Volume I|publisher=Phaidon|year=2004|location=London|isbn=978-0-7148-4285-1}}{{cite book|last=James|first=Christopher|title=The Book of Alternative Photographic Processes|edition=2nd|publisher=Delmar Cengage Learning|year=2009|location=Clifton Park, NY|url=https://archive.org/details/bookofalternativ0000jame|isbn=978-1-4180-7372-5|access-date=2009-08-11|url-access=registration}}{{cite web|publisher=New York Public Library|work=Seeing is Believing: 700 years of scientific and medical illustration|title=Photography. Cyanotype photograph. Anna Atkins (1799-1871)|date=2001|orig-year=1843|url=http://seeing.nypl.org/235bt.html|access-date=2009-08-11}}{{cite book|last=Peres|first=Michael R.|title=The Focal Encyclopedia of Photography: Digital Imaging, Theory and Applications, History, and Science|edition=4th|publisher=Elsevier/Focal Press|year=2007|location=Amsterdam; Boston|isbn=978-0-240-80740-9}}

• Copley Medal: Jean-Baptiste Dumas{{cite web |title=Copley Medal {{!}} British scientific award |url=https://www.britannica.com/science/Copley-Medal |website=Encyclopedia Britannica |access-date=16 February 2020 |language=en}}
• Wollaston Medal for Geology: Jean-Baptiste Elie de Beaumont; Pierre Armand Dufrenoy

• January 13 – David Ferrier (died 1928), Scottish neurologist.{{cite ODNB|id=33117|title=Ferrier, Sir David (1843–1928), neurologist | author1= Sherrington, C. S. | author2 = Bevan, Michael|url=https://www.oxforddnb.com/view/10.1093/ref:odnb/9780198614128.001.0001/odnb-9780198614128-e-33117|accessdate=16 February 2020 }}
• May 6 – G. K. Gilbert (died 1918), American geologist.
• June 12 – David Gill (died 1914), Scottish astronomer.
• June 23 – Paul Heinrich von Groth (died 1927), German mineralogist.
• July 24 – William de Wiveleslie Abney (died 1920), English astronomer.
• August 17 – Alexandre Lacassagne (died 1924), French forensic scientist.
• November 30 – Martha Ripley (died 1912), American physician.{{cite book |last1=Ogilvie |first1=Marilyn Bailey |last2=Harvey |first2=Joy Dorothy |author-link1=Marilyn Bailey Ogilvie |author-link2=Joy Harvey |title=The Biographical Dictionary of Women in Science: L-Z |date=2000 |publisher=Taylor & Francis |isbn=978-0-415-92040-7 |page=1102 |url=https://books.google.com/books?id=LTSYePZvSXYC&pg=PA1102 |language=en}}
• December 11 – Robert Koch (died 1910), German physician, famous for the discovery of the tubercle bacillus (1882) and the cholera bacillus (1883) and for his development of Koch's postulates; awarded the Nobel Prize in Physiology or Medicine in 1905
• Adelaida Lukanina (died 1908), Russian chemist.

• July 25 – Charles Macintosh (born 1766), Scottish inventor of a waterproof fabric.{{cite book |last1=Day |first1=Lance |last2=McNeil |first2=Ian |title=Biographical Dictionary of the History of Technology |date=11 September 2002 |publisher=Routledge |isbn=978-1-134-65019-4 |page=786 |url=https://books.google.com/books?id=FmoTeX3aGl4C&dq=Charles+Macintosh+29+december+1766&pg=PA786 |language=en}}
• August 10 – Robert Adrain (born 1775), Irish American mathematician.
• September 11 – Joseph Nicollet (born 1786), French geographer, explorer, mathematician and astronomer.
• September 19 – Gaspard-Gustave Coriolis (born 1792), French mathematician and discoverer of the Coriolis effect.
• September 30 – Richard Harlan (born 1796), American zoologist.
• November 16 – Abraham Colles (born 1773), Anglo-Irish surgeon.

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Category:19th century in science

Category:1840s in science