1865 in science

Archaeology

• John Lubbock publishes Pre-historic Times, as Illustrated by Ancient Remains, and the Manners and Customs of Modern Savages, including his coinage of the term Palæolithic.

  Astronomy

• Vassar College Observatory opens at Poughkeepsie, New York, with Maria Mitchell as its first director.

  Chemistry

• Friedrich Kekulé proposes a ring structure for benzene.
• Adolf von Baeyer begins work on indigo dye, a milestone in modern industrial organic chemistry which revolutionizes the dye industry.
• Johann Josef Loschmidt determines the exact number of molecules in a mole, later named Avogadro's number.

  Life sciences

• Louis Pasteur shows that the air is full of bacteria.
• Joseph Lister begins to experiment with antiseptic surgery in Glasgow using carbolic acid.
• Max Schultze gives the first known description of the platelet.
• Claude Bernard publishes Principes de Médecine experimentale.
• February 8 & March 8 – Gregor Mendel reads his paper, Versuche über Pflanzenhybriden, at two meetings of the Natural History Society of Brünn in Moravia.
• May 17 – Father Armand David first observes Père David's Deer in China.
• June-August – Francis Galton formulates eugenics.
• September – John Henry Walsh gives the first definition of a dog breed standard based on physical form.
• September 28 – Elizabeth Garrett Anderson obtains a licence from the Society of Apothecaries in London to practice medicine, the first woman to qualify as a doctor in the United Kingdom, and sets up in her own practice.

  Physics

• Rudolf Clausius gives the first mathematical version of the concept of entropy, and also names it.
• James Clerk Maxwell publishes A Dynamical Theory of the Electromagnetic Field.

  Technology

• Aveling and Porter produce the world's first steam roller at Rochester in England.
• Hermann Sprengel produces the Sprengel pump which is capable of creating a significant vacuum.

  Awards

• Copley Medal: Michel Chasles
• Wollaston Medal in Geology: Thomas Davidson

  Births

• January 22 – Friedrich Paschen, German physicist.
• February 1 – Henry Luke Bolley, American plant pathologist.
• March 19 – William Morton Wheeler, American entomologist.
• March 31 – Anandi Gopal Joshi, Indian physician.
• April 28 – Charles W. Woodworth, American entomologist.
• June 27 – John Monash, Australian civil engineer and General.
• August 10 – Charles Close, Jersey-born cartographer.
• October 12 – Arthur Harden, English biochemist, Nobel Prize in Chemistry recipient.
• November 4 – Chevalier Jackson, American laryngologist and pioneer of endoscopy.

  Deaths

• January 14 – Marie-Anne Libert, Belgian botanist.
• January 31 – Hugh Falconer, British geologist, botanist, paleontologist and paleoanthropologist.
• April 23 – Diego de Argumosa, Spanish surgeon.
• April 30 – Robert FitzRoy, English admiral and meteorologist, suicide.
• May 27 – Charles Waterton, English naturalist and explorer.
• July 25 – Dr. James Barry, Irish-born military surgeon.
• August 12 – Sir William Jackson Hooker, English botanist.
• August 13 – Ignaz Semmelweis, Hungarian physician, following restraint in insane asylum.
• August 26 – Johann Franz Encke, German astronomer.
• August 29 – Robert Remak, Polish/Prussian Jewish embryologist.
• September 2 – Sir William Rowan Hamilton, Irish mathematician, physicist and astronomer.
• October 17 – Joseph-François Malgaigne, French surgeon.