1840 in science
- William Whewell publishes The Philosophy of the Inductive Sciences, introducing the terms scientist (for the second time) and physicist.
- Justus von Liebig publishes Die Organische Chemie in ihre Anwendung auf Agricultur und Physiologie in Braunschweig, emphasising the importance of agricultural chemistry in crop production; it will go through at least eight editions.
- The first known photograph of Niagara Falls, a daguerreotype, is taken by English chemist Hugh Lee Pattinson.
- Germain Hess proposes Hess's law, an early statement of the law of conservation of energy, which establishes that energy changes in a chemical process depend only on the states of the starting and product materials and not on the specific pathway taken between the two states.
- George Richards Elkington patents the electroplating process invented by surgeon John Wright of Birmingham in England.
- Louis Agassiz publishes his Etudes sur les glaciers, the first major scientific work to propose that the Earth has seen an ice age.
- January 19 – Captain Charles Wilkes' United States Exploring Expedition sights Wilkes Land, providing evidence that Antarctica is a complete continent.
- January 21 – Adélie Land first visited by Jules Dumont d'Urville in the French ship Astrolabe.
- The Nemesis (1839) becomes the first iron ship to sail around the Cape of Good Hope, aided by techniques to adjust the compass for the effect of an iron hull developed the year before by George Biddell Airy, the Astronomer Royal.
History of science
- Publication begins in Paris of the Œuvres complètes d’Ambroise Paré edited by Joseph-François Malgaigne.
- Joseph Whitworth introduces his precision "end measurements" technique.
- Carl Friedrich Gauss publishes his Dioptrische Untersuchungen, in which he gives the first systematic analysis of the formation of images under a paraxial approximation (Gaussian optics).
- January 21 – Sophia Jex-Blake (died 1912), English physician.
- February 4 – Hiram Maxim (died 1916), inventor of the machine gun.
- February 5 – John Boyd Dunlop (died 1921), inventor.
- February 10 – Per Teodor Cleve (died 1905), chemist.
- March 28 – Emin Pasha (died 1892), explorer.
- March 31 – Benjamin Baker (died 1907), civil engineer.
- April 9 – Praskovya Uvarova (died 1924), Russian archaeologist.
- April 22 – Thomas Clouston (died 1915), psychiatrist.
- August 4 – Richard von Krafft-Ebing (died 1902), sexologist.
- November 24 – John Brashear (died 1920), astronomer.
- November 29 – James Crichton-Browne (died 1938), psychiatrist.
- March 2 – Heinrich Wilhelm Matthias Olbers (born 1758), German astronomer.
- March 23 – William Maclure (born 1763), Scottish American geologist.
- April 25 – Siméon Denis Poisson (born 1781), French mathematician.
- April 29 – Pierre Jean Robiquet (born 1780), French chemist.
- July 4 – Karl Ferdinand von Gräfe (born 1787), German surgeon.
- November 2 – Sir Anthony Carlisle (born 1768), English surgeon.
- December 11 – Franz Bauer (born 1758), Moravian-born botanical illustrator.
- Whewell, William (1840). "Introduction". The Philosophy of the Inductive Sciences, founded upon their history. 1. London: J. W. Parker. pp. 113, 71.
- "scientist, n". Oxford English Dictionary online version. Oxford University Press. September 2011. Retrieved 2011-12-02. (subscription or UK public library membership required)
- "physicist, n". Oxford English Dictionary online version. Oxford University Press. September 2011. Retrieved 2011-12-02.
- Black, George W. (1978). "Justus Liebig's Contribution to Agricultural Chemistry". Journal of Chemical Education. American Chemical Society. 55: 33. Bibcode:1978JChEd..55...33B. doi:10.1021/ed055p33.1. Retrieved 2011-06-21.
- "Hess, Germain Henri". Archived from the original on 2007-02-09. Retrieved 2007-03-12.
- "Antarctic Exploration — Chronology". Quark Expeditions. 2004. Archived from the original on 2006-09-08. Retrieved 2006-10-20.
- Guillon, Jacques (1986). Dumont d'Urville. Paris: France-Empire. ISBN 2-7048-0472-9.
- Headrick, Daniel R. (1981). The Tools of Empire: Technology and European Imperialism in the Nineteenth Century. New York: Oxford University Press. ISBN 0-19-502832-5.
- Bühler, Walter Kaufmann (1987). Gauss: a biographical study. Springer-Verlag. pp. 144–145. ISBN 0-387-10662-6.
- Hecht, Eugene (1987). Optics. Addison Wesley. p. 134. ISBN 0-201-11609-X.