1861 in science
- March 30 – William Crookes announces his discovery of thallium.
- Rubidium is discovered by Robert Bunsen and Gustav Kirchhoff, in Heidelberg, Germany, in the mineral lepidolite through the use of their spectroscope.
- Aleksandr Butlerov is instrumental in creating the theory of chemical structure.
- Josef Loschmidt publishes Chemische Studien, proposing two-dimensional representations for over 300 molecules and recognising variations in atomic size.
- Ernest Solvay develops the Solvay process for the manufacture of soda ash (sodium carbonate).
Medicine and physiology
- Paul Broca identifies the speech production center of the brain.
- Franciscus Donders introduces the term visual acuity.
- Guillaume Duchenne describes Duchenne muscular dystrophy.
- Prosper Ménière reports the association of vertigo with inner ear disorders.
- Ádám Politzer publishes the technique of Politzerization used in otorhinolaryngology.
- Ignaz Semmelweis publishes Die Ätiologie, der Begriff und die Prophylaxis des Kindbettfiebers, a treatment of his theory on sanitary conditions during childbirth.
- September – First complete identified skeleton of Archaeopteryx unearthed near Langenaltheim, Germany.
- January 1 – First steam-powered carousel recorded, in Bolton, England.
- William Froude publishes the first results of his research into ship hull design.
- Dr. Richard J. Gatling invents the Gatling gun.
- James Clerk Maxwell demonstrates the principle of permanent three-colour photography.
- Michael Faraday's Royal Institution Christmas Lectures published as The Chemical History of a Candle.
- February 15 – Alfred North Whitehead (died 1947), English mathematician.
- April 24 – Hedda Andersson (died 1950), Swedish physician
- May 20 – Henry Gantt (died 1919), American project engineer.
- June 9 – Pierre Duhem (died 1916), French philosopher of science.
- July 18 – Kadambini Ganguly (died 1923), Indian physician.
- July 26 – Ægidius Elling (died 1949), Norwegian gas turbine pioneer.
- August 9 – Dorothea Klumpke (died 1942), American astronomer.
- December 17 – Arthur E. Kennelly (died 1939), Irish American electrical engineer.
- January 3 – Arnold Adolph Berthold (born 1803), German physiologist.
- May 16 – John Stevens Henslow (born 1796), English botanist.
- June 18 – Eaton Hodgkinson (born 1789), English structural engineer.
- November 10 – Isidore Geoffroy Saint-Hilaire (born 1805), French zoologist.
- November 13 – Sir John Forbes (born 1787), Scottish-born royal physician.
- December 10 – Thomas Southwood Smith (born 1788), English physician and sanitary reformer.
- Ferdinand Deppe (born 1794), German naturalist, explorer and painter.
- Kirchhoff, G.; Bunsen, R. (1861). "Chemische Analyse durch Spectralbeobachtungen". Annalen der Physik und Chemie. 189 (7): 337–381. Bibcode:1861AnP...189..337K. doi:10.1002/andp.18611890702. Retrieved 2011-11-21.
- Weeks, Mary Elvira (1932). "The discovery of the elements. XIII. Some spectroscopic discoveries". Journal of Chemical Education. 9 (8): 1413–1434. Bibcode:1932JChEd...9.1413W. doi:10.1021/ed009p1413. Retrieved 2011-11-21.
- Kazansky, B.; Bykov, G. V., eds. (1961). Centenary of the Theory of Chemical Structure: collection of papers by A. M. Butlerov. Moscow: Publishing House of the USSR Academy of Sciences.
- Rzepa, Henry S. (2005). "Joseph Loschmidt: Structural formulae, 1861". Archived from the original on 16 May 2011. Retrieved 2011-05-23.
- "Guillaume Benjamin Amand Duchenne de Boulogne". WhoNamedIt?. Archived from the original on 25 May 2011. Retrieved 2011-05-27.
- Natural History Museum (London) BMNH 37001. Chiappe, Luis M. (2007). Glorified Dinosaurs. Sydney: UNSW Press. pp. 118–146. ISBN 0-471-24723-5.
- "Fairground Rides – A Chronological Development". National Fairground Archive. University of Sheffield. 2007. Archived from the original on 2011-08-11. Retrieved 2011-08-24.
- "On the rolling of ships." Transactions of the Institution of Naval Architects 2 (1861): pp. 180–227; 3 (1862): pp. 45–62.
- Greeley, Horace; Case, Leon (1872). The Great Industries of the United States. Hartford: J.B. Burr & Hyde. p. 944.
- The Hutchinson Factfinder. Helicon. 1999. ISBN 1-85986-000-1.