1899 in science

Astronomy

• December 2 – During the new moon, a near-grand conjunction of the classical planets and several binocular Solar System bodies occur. The Sun, Moon, Mercury, Mars and Saturn are all within 15° of each other, with Venus 5° ahead of this conjunction and Jupiter 15° behind. Accompanying the classical planets in this grand conjunction are Uranus, Ceres and Pallas.
• The 80 cm refracting telescope is completed at Potsdam Observatory.

  Biology

• May 1 – The National Trust in the United Kingdom acquires its first part of Wicken Fen, making it the country's oldest wetland nature reserve.
• November 8 – The New York Zoological Society opens the Bronx Zoological Park to the public in New York City under the direction of William Temple Hornaday.

  Chemistry

• Actinium is discovered by Andre-Louis Debierne.
• International Committee on Atomic Weights established.

  Exploration

• January 23 – The British Southern Cross Expedition crosses the Antarctic Circle. Later in the year, it first charts Duke of York Island.

  Mathematics

• Élie Cartan first defines the exterior derivative in its modern form.
• David Hilbert publishes Grundlagen der Geometrie, proposing a formal set, Hilbert's axioms, to replace Euclid's elements.
• Georg Alexander Pick publishes his theorem on the area of simple polygons.

  Medicine

• Bubonic plague enters Brazil through the seaport of Santos.
• March 6 – Felix Hoffmann patents Aspirin and Bayer registers its name as a trademark.
• October 2 – The London School of Hygiene & Tropical Medicine is established by Patrick Manson at the Albert Dock Seamen's Hospital.

  Physics

• Ernest Rutherford classifies two types of radiation, alpha rays and beta rays.
• Henri Becquerel discovers that radiation from uranium consists of charged particles and can be deflected by magnetic fields.
• Hertha Ayrton becomes the first woman to read her own paper before the Institution of Electrical Engineers in London, of which soon afterwards she is elected the first female member.

  Technology

• February 14 – Voting machines are approved by the U.S. Congress for use in federal elections.
• Hugo Lenz first demonstrates Lenz poppet valve gear, for stationary steam engines.
• The world's first successful self-propelled steam fire engine, the 'Fire King', is built by Merryweather & Sons in London and dispatched to Port Louis on Mauritius.

  Awards

• Copley Medal: Lord Rayleigh
• Wollaston Medal for Geology: Charles Lapworth

  Births

• January 12 – Paul Hermann Müller, Swiss chemist, winner of the Nobel Prize in Physiology or Medicine in 1948.
• February 27 – Charles Best, American-born medical scientist.
• April 11 – Percy Lavon Julian, African American research chemist.
• April 28 – Mary Loveless, née Hewitt, American immunologist.
• May 8 – Charles Illingworth, English surgeon.
• July 3 – Ludwig Guttmann, German-born neurologist and pioneer of paralympic games.
• July 7 – Anna Baetjer, American toxicologist.
• July 26 – Bill Hamilton, New Zealand mechanical engineer.
• September 3 – Frank Macfarlane Burnet, Australian virologist best known for his contributions to immunology, winner of the Nobel Prize in Physiology or Medicine in 1960.
• September 29 – László Bíró, Hungarian inventor.
• October 18 – Janet Vaughan, English physiologist.
• October 27 – Nikolay Dollezhal, a key figure in Soviet atomic bomb project and chief designer of nuclear reactors.
• November 10 – Helen Porter, English plant physiologist.

  Deaths

• January 4 – Henry Alleyne Nicholson, British palaeontologist and zoologist.
• February 18 – Sophus Lie, Norwegian mathematician.
• March 18 – Othniel Charles Marsh, American paleontologist.
• July 16 – Margaretta Riley, British botanist.
• August 9 – Edward Frankland, English chemist.
• August 16 – Robert Bunsen, German chemist, perfector of the bunsen burner.
• October 28 – Ottmar Mergenthaler, German American inventor.