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The year 1691 in science and technology involved some significant events.
Biology
- Italian Jesuit scholar Filippo Bonanni publishes the results of his microscopic observations of invertebrates in Observationes circa Viventia, quae in Rebus non-Viventibus.
Mathematics
- Gottfried Leibniz discovers the technique of separation of variables for ordinary differential equations.
- Michel Rolle invents Rolle's theorem.
Medicine
- Anton Nuck's Adenographia curiosa et uteri foeminei anatome nova is published at Leiden, including a description of the canal of Nuck and a demonstration that the embryo is derived from the ovary and not the sperm.
Technology
- Edmond Halley devises a diving bell.
- In music, the "equal temperament scale" used in modern music is developed by organist Andreas Werckmeister.
Births
- November 18 – Mårten Triewald, Swedish mechanical engineer (died 1747)
Deaths
- January 17 – Richard Lower, English physician who performed the first direct blood transfusion (born 1631)
- December 31 – Robert Boyle, Anglo-Irish chemist (born 1627)