1669 in science

The year 1669 in science and technology involved some significant events.

Astronomy

 * February 23 – Isaac Newton writes his first description of his new invention, the reflecting telescope.
 * Geminiano Montanari detects the variability of the eclipsing binary Algol.
 * Jean Picard begins measurement of 1 degree of Earth's meridian arc in France.

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 German alchemist Hennig Brand, the first chemical element to be discovered that was not known since ancient times.

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 (calcite).
 * Robert Boyle publishes A Continuation of New Experiments Physico-mechanical, Touching the Spring and Weight of the Air, and Their Effects.

Physiology and medicine

 * Richard Lower publishes his Tractatus de Corde on the workings of the heart.
 * The Chinese traditional herbal medicine company Tong Ren Tang (同仁堂) is established in Beijing by imperial physician Yue Xianyang.

Publications

 * Isaac Barrow publishes Lectiones Opticæ et Geometricæ in London.

Births

 * May 26 – Sébastien Vaillant, French botanist (died 1722)

Deaths

 * April 12 – Abdias Treu, German mathematician (born 1597)
 * c. April – Nicasius le Febure, French-born royal chemist, alchemist and apothecary (born 1615)