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.<ref>Template:Cite book</ref>
• 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".<ref>Philosophical Transactions of the Royal Society 4: pp. 963–965.</ref>
• 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,<ref>Template:Cite book</ref> the first chemical element to be discovered that was not known since ancient times.<ref>Template:Cite journal</ref>

Geology

• Nicolas Steno puts forward his theory that sedimentary strata had been deposited in former seas, and that fossils are organic in origin.<ref>De solido intra solidum naturaliter contento dissertationis prodromus.</ref>

Mathematics

• October 29 – Isaac Newton is appointed Lucasian Professor of Mathematics at the University of Cambridge.<ref>Template:Cite book</ref>

Physics

• Rasmus Bartholin publishes his observation of the birefringence of a light ray by Iceland spar (calcite).<ref>Template:Cite book English translation: Experiments with the double refracting Iceland crystal which led to the discovery of a marvelous and strange refraction tr. by Werner Brandt. Westtown, Pa., 1959.</ref>
• 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)