1921 in science

Cartography

• Winkel tripel projection proposed.

  Chemistry

• Étienne Biéler and James Chadwick publish a key paper on the strong interaction.
• Thomas Midgley discovers the effective anti-knocking properties of tetraethyllead, which is used in "leaded" gasoline.

  Exploration

• Danish explorer Lauge Koch first sets foot on and names Kaffeklubben Island, the northernmost point of land on Earth.

  Mathematics

• John Maynard Keynes publishes A Treatise on Probability.
• Marston Morse applies the Thue–Morse sequence to differential geometry.
• Emmy Noether publishes Idealtheorie in Ringbereichen, developing ideal ring theory, an important text in the field of abstract algebra.
• First publication of Ludwig Wittgenstein's Tractatus Logico-Philosophicus, as "Logisch-Philosophische Abhandlung" in Annalen der Naturphilosophie.

  Medicine

• April–August – Nicolae Paulescu publishes papers on the preparation and therapeutic effects in animal subjects of an aqueous pancreatic extract.
• July 18 – The first BCG vaccination against tuberculosis.
• July 27 – Researchers at the University of Toronto led by biochemist Frederick Banting announce the discovery of the hormone insulin.
• American biochemist Elmer McCollum identifies the presence of a component in cod liver oil which cures rickets, which he calls vitamin D.
• Fidel Pagés pioneers epidural anesthesia.

  Physics

• July – Wolfgang Pauli is awarded his Doctor of Philosophy at Ludwig Maximilian University of Munich for his thesis Über das Modell des Wasserstoff-Molekülions.
• T. Kaluza demonstrates that a five-dimensional version of Albert Einstein's equations unifies gravitation and electromagnetism.

  Psychology

• Hermann Rorschach publishes Psychodiagnostik, proposing the inkblot test.
• Gaëtan Gatian de Clérambault publishes Les Psychoses passionelles, a comprehensive review of erotomania.

  Technology

• October 25 – Hugo A. F. Abt is granted a patent for his design of bascule bridge.
• The vibraphone in its original form is invented in the United States.

  Institutions

• Journalist E. W. Scripps and biologist William Emerson Ritter found Science Service, later renamed Society for Science and the Public, in the United States with the goal of keeping the public informed of scientific developments.

  Awards

• Nobel Prize
• * Physics – Albert Einstein – awarded 1922
• * Chemistry – Frederick Soddy
• * Physiology or Medicine – not awarded

  Births

• January 18 – Yoichiro Nambu, Japanese-American nuclear physicist, recipient of the Nobel Prize in Physics.
• February 3 – Ralph Asher Alpher, American cosmologist.
• March 11 – Léopold Reichling, Luxembourg biologist and naturalist.
• April 21 – John R. Huizenga, American nuclear physicist.
• April 30
• * Roger L. Easton, American physicist, principal inventor of the Global Positioning System.
• * Ralph A. Lewin, Anglo-American biologist, "the father of green algae genetics".
• May 18 – Olgierd Zienkiewicz, British civil engineer.
• June 1 – Giuliana Tesoro, Italian-American organic chemist.
• June 9 – Forrest Bird, American biomedical engineer.
• June 14 – George Rédei, Hungarian biologist.
• June 15 – Gavriil Ilizarov, Polish-born orthopedic surgeon.
• June 26 – Anne Beloff-Chain, British biochemist.
• July 4 – Aron Arthur Moscona, American developmental biologist.
• July 18 – John Glenn, American astronaut.
• August 16 – Rudolf Trümpy, Swiss geologist.
• October 5 – Mahlon Hoagland, American biochemist, discoverer of transfer RNA.
• October 18 – Beatrice Helen Worsley, Mexican-born Canadian computer scientist.
• October 21 – Victor A. McKusick, American "father of genetic medicine".
• December 2 – Isabella Karle, American physical chemist.

  Deaths

• March 11 – Sherburne Wesley Burnham, American astronomer.
• March 29 – John Burroughs, American naturalist.
• June 7 – Hans Christian Cornelius Mortensen, Danish ornithologist.
• August 29 – Joel Asaph Allen, American zoologist.
• October 23 – John Boyd Dunlop, British inventor.
• December 12 – Henrietta Swan Leavitt, American astronomer.