1900 in science

Aeronautics

• July 2 – The first rigid airship flight is made by the LZ1 designed by Ferdinand von Zeppelin.
• c. October 3 – The Wright brothers begin their first manned glider experimental flights at Kitty Hawk, North Carolina.

  Chemistry

• Moses Gomberg identifies the first organic radical, triphenylmethyl radical.
• Johannes Rydberg refines the expression for observed hydrogen line wavelengths.

  Earth sciences

• Richard Dixon Oldham distinguishes between primary, secondary and tertiary waveforms as recorded by seismometers.

  Exploration

• American explorer Robert Peary first sights Kaffeklubben Island, the northernmost point of land on Earth.

  Genetics

• Hugo de Vries publishes the results of his experiments in Mendelian inheritance.

  Mathematics

• Max Dehn introduces two examples of Dehn plane and the Dehn invariant.
• David Hilbert states his list of 23 problems which show where some further mathematical work is needed.
• Russell's paradox is first discovered by Ernst Zermelo but he does not publish it, and it is known only to Hilbert, Husserl and other members of the University of Göttingen.
• Gaston Tarry confirms Euler's conjecture that no 6×6 orthogonal Graeco-Latin square is possible.
• Alfred Young introduces the Young tableau.

  Medicine

• German gynecologist Hermann Johannes Pfannenstiel publishes his description of the "Pfannenstiel incision", a transverse incision used in genitourinary surgery that continues to be widely used.

  Paleontology

• Barnum Brown finds the first partial skeleton of Tyrannosaurus rex in eastern Wyoming.
• Dr. James K. Hampson identifies the Island 35 Mastodon skeleton in the Mississippi River.

  Photography

• Kodak introduce their first Brownie.

  Physics

• April 26 – Guglielmo Marconi patents the tuned circuit.
• October 19 – Max Planck produces Planck's law of black-body radiation and Planck constant, marking the birth of quantum physics.
• December 7 – Max Planck states his quantum hypothesis.
• December 23 – Reginald Fessenden, experimenting with a high-frequency spark transmitter, successfully transmits speech over a distance of about 1.6 kilometers, from Cobb Island, Maryland, which appears to have been the first audio radio transmission.
• Gamma rays discovered by Paul Villard while studying uranium decay.

  Physiology

• Karl Landsteiner makes the first discovery of blood types, identifying the ABO blood group system.
• Carl Rasch coins the term 'polymorphous light eruption'.
• Jōkichi Takamine and Keizo Uenaka discover adrenaline.

  Psychology

• Sigmund Freud's Die Traumdeutung is published.

  Zoology

• Richard J. Ussher and Robert Warren publish The Birds of Ireland.

  Awards

• Copley Medal: Marcellin Berthelot

  Births

• January 2 – Una Ledingham, English physician specialising in diabetes mellitus and pregnancy.
• March 4 – Heinrich Willi, Swiss pediatrician.
• March 8 – Howard H. Aiken, American computing pioneer.
• March 19 – Frédéric Joliot, French physicist.
• April 3 – Albert Ingham, English mathematician.
• April 25 – Wolfgang Pauli, Austrian-born physicist.
• April 26 – Charles Richter, American geophysicist and inventor.
• April 28 – Jan Oort, Dutch astronomer.
• May 5 – Helen Redfield, American geneticist.
• May 6 – Zheng Ji, Chinese biochemist and nutritionist.
• May 10 – Cecilia Payne-Gaposchkin, English-born American astronomer and astrophysicist.
• May 22 – Honor Fell, English biologist.
• June 24 – Wilhelm Cauer, German mathematician and electronic engineer.
• June 25 – Philip D'Arcy Hart, English medical researcher, pioneer in tuberculosis treatment.
• June 30 – James Stagg Scottish-born meteorologist.
• July 9 – Frances McConnell-Mills, born Frances Mary McConnell, American toxicologist.
• August 25 – Hans Adolf Krebs, German-born medical doctor and biochemist.
• August 26 – Hellmuth Walter, German-born engineer and inventor.
• October 2 – Isabella Forshall, English pediatric surgeon.
• November 5 – Ethelwynn Trewavas, English ichthyologist.
• December 9 – Joseph Needham, English biochemist and writer on the history of science and technology in China.
• December 12 – Mária Telkes, Hungarian-American scientist and inventor.
• December 17 – Mary Cartwright, English mathematician, one of the first people to analyze a dynamical system with chaos.
• Robina Addis, English pioneering professional psychiatric social worker.
• Ernest Gibbins, English entomologist.

  Deaths

• January 13 – Peter Waage, Norwegian chemist.
• January 22 – David E. Hughes, British-American inventor.
• March 6 – Gottlieb Daimler, German engineer, automotive pioneer.
• March 10 – George James Symons, English meteorologist.
• April 1 – George Jackson Mivart, English biologist.
• August 4 – Étienne Lenoir, Belgian mechanical engineer.
• August 31 – John Bennet Lawes, English agricultural scientist.
• October 16 – Henry Acland, English physician.
• October 29 – Bruno Abakanowicz, Polish mathematician, inventor and electrical engineer.