1691 in science

Astronomy

• The Hartmann Mask is invented by Christopher Scheiner.

  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 today's music is developed by organist Andreas Werckmeister.

  Births

• November 18 – Mårten Triewald, Swedish mechanical engineer

  Deaths

• January 17 – Richard Lower, English physician who performed the first direct blood transfusion
• December 31 – Robert Boyle, British chemist