1669 in science

Astronomy

• Geminiano Montanari detects the variability of the eclipsing binary Algol.

  Biology

• Marcello Malpighi publishes Dissertatio Epistolica de Bombyce in London, a study of Bombyx mori which is the first published monograph on an invertebrate.
• Robert Morison publishes Praeludia Botanica, emphasising use of the structure of a plant's fruits for its classification.
• Francis Willughby and John Ray publish "Experiments concerning the motion of sap in trees, made this spring".
• Jan Swammerdam publishes Historia Insectorum Generalis in the Netherlands, explaining the process of metamorphosis in insects.

  Chemistry

• Phosphorus is discovered by Hennig Brand.

  Geology

• Nicolas Steno puts forward his theory that sedimentary strata had been deposited in former seas, and that fossils are organic in origin.

  Mathematics

• October 29 – Isaac Newton is appointed Lucasian Professor of Mathematics at the University of Cambridge.

  Physics

• Rasmus Bartholin publishes his observation of the birefringence of a light ray by Iceland spar.

  Physiology and medicine

• Richard Lower publishes his Tractatus de Corde on the workings of the heart.

  Publications

• Isaac Barrow publishes Lectiones Opticæ et Geometricæ in London.

  Births

• May 26 – Sébastien Vaillant, French botanist

  Deaths

• Nicasius le Febure, French chemist