1791 in science

Biology

• Jean Baptiste François Pierre Bulliard begins publication of Histoire des champignons de la France, a significant text in mycology.
• Luigi Galvani publishes his discoveries in "animal electricity".

  Chemistry

• Nicolas Leblanc patents the Leblanc process for the production of soda ash from common salt.
• The element Titanium is discovered included in ilmenite in Cornwall, England, by local amateur geologist Rev. William Gregor.

  Mathematics

• American statesmen Thomas Jefferson introduces the highest averages method of voting which also becomes known as the D'Hondt method.

  Medicine

• May 7 – Irish surgeon Samuel Croker-King first describes his trepanning device.

  Metrology

• March – In France, the National Constituent Assembly accepts the recommendation of its Commission of Weights and Measures that the nation should adopt the metric system.

  Physics

• Pierre Prévost shows that all bodies radiate heat, no matter how hot or cold they are.

  Technology

• James Rumsey is granted a patent related to fluid power engineering, in England.

  Publications

• Sir John Sinclair's Statistical Account of Scotland begins publication, introducing the term Statistics into English.

  Awards

• Copley Medal: James Rennell; Jean-André Deluc

  Births

• March 20 – John Farey, English mechanical engineer and technical writer
• April 9 – George Peacock, English mathematician
• April 27 – Samuel F. B. Morse, American inventor
• July 13 – Allan Cunningham, English botanist and explorer
• September 4 – Robert Knox, Scottish anatomist
• September 22 – Michael Faraday, English chemist and physicist
• September 23 – Johann Franz Encke, German astronomer
• December 26 – Charles Babbage, English mathematician and inventor of computing machines

  Deaths

• July 24 – Ignaz von Born, Hungarian metallurgist
• Date unknown – Maria Petraccini, Italian anatomist and physician