1861 in science

Astronomy

• May 13 – Comet C/1861 J1 first observed from Australia by John Tebbutt.

Biology

• Anton de Bary publishes his first work on fungi, describing sexual reproduction in Peronospora.
• Charles Thorp, Archdeacon of Durham, arranges purchase of some of the Farne Islands off the north-east coast of England and employment of a warden to protect threatened seabird species.

Chemistry

• 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.

Earth sciences

• Eduard Suess proposes the former existence of the supercontinent Gondwana.

History of science and technology

• Boulton and Watt rotative beam engine of 1788 from the makers' Soho Foundry in the west midlands of England is acquired for the Museum of Patents, predecessor of the Science Museum, London.
• First volumes of Munk's Roll published.

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 Etiology, Concept and Prophylaxis of Childbed Fever , a treatment of his theory on sanitary conditions during childbirth.
• Adolf Zsigmondy develops a dental notation system.

Paleontology

• August 15 – First description of Archaeopteryx, based on a feather found in Bavaria; in September the first complete identified skeleton is found near Langenaltheim in Germany.

Technology

• January 1 – First steam-powered carousel recorded, in Bolton, England.
• May 17 – Scottish-born physicist James Clerk Maxwell demonstrates the principle of permanent three-colour photography in a lecture at the Royal Institution in London using a photograph captured by Thomas Sutton.
• July 23 – The term 'drive shaft' is used in the description of the mechanism in a patent reissue for the Watkins and Bryson horse-drawn mowing machine.
• William Froude publishes the first results of his research into ship hull design.
• Dr. Richard J. Gatling invents the Gatling gun.
• Capt. Robert P. Parrott is granted a United States patent for the Parrott rifle, a field artillery weapon.
• German scientist Philipp Reis succeeds in creating a device that captures sound and converts it to electrical impulses which are transmitted via electrical wires to another device that transforms these pulses into recognizable sounds similar to the original acoustical source. Reis coins the term telephone to describe his device, the Reis telephone.

Publications

• Michael Faraday's Royal Institution Christmas Lectures published as The Chemical History of a Candle.

Awards

• Copley Medal: Louis Agassiz
• Wollaston Medal for geology: Heinrich Bronn

Births

• February 12 – Lou Andreas-Salomé, born Luíza von Salomé, Russian-born psychoanalyst.
• February 15
• * Charles Édouard Guillaume, French physicist, recipient of the Nobel Prize in Physics.
• * Alfred North Whitehead, English mathematician.
• April 24 – Hedda Andersson, Swedish physician.
• May 5 – Peter Cooper Hewitt, American electrical engineer and inventor.
• May 20 – Henry Gantt, American project engineer.
• June 9 – Pierre Duhem, French philosopher of science.
• June 20 – Frederick Hopkins, British biochemist, recipient of the Nobel Prize for Physiology or Medicine.
• July 7 – Nettie Stevens, American geneticist.
• July 18 – Kadambini Ganguly, Indian physician.
• July 26 – Ægidius Elling, Norwegian gas turbine pioneer.
• August 4 – Henry Head, English neurologist.
• August 9 – Dorothea Klumpke, American astronomer.
• August 10 – Almroth Wright, English bacteriologist and immunologist.
• October 11 – John Bell Hatcher, American paleontologist.
• December 17 – Arthur E. Kennelly, Irish American electrical engineer.

Deaths

• January 3 – Arnold Adolph Berthold, German physiologist.
• May 16 – John Stevens Henslow, English botanist.
• June 13 – Henry Gray, English anatomist.
• June 18 – Eaton Hodgkinson, English structural engineer.
• November 10 – Isidore Geoffroy Saint-Hilaire, French zoologist.
• November 13 – Sir John Forbes, Scottish-born royal physician.
• December 10 – Thomas Southwood Smith, English physician and sanitary reformer.
• Ferdinand Deppe, German naturalist, explorer and painter.