Dutch diplomat Christiaan Huygens (1629–1695) made contributions to the grinding of lenses for microscopes and telescopes, observed Saturn’s rings, and developed a wave theory of light, among other accomplishments. In mathematics, he is best known for using geometrical principles to invent the pendulum clock. His 1673 treatise on that subject was titled Horologium Oscillatorium and received an imprimatur from the King of France.


He included several diagrams of pendulums.

Huygens’s geometrical propositions and proofs also stimulated work on the cycloid and other curves.

Reference
Yoder, Joella G. 2005. Christiaan Huygens, Book on the Pendulum Clock (1673). In Landmark Writings in Western Mathematics, 1640–1940, edited by Ivor Grattan-Guinness, 33–45. Amsterdam: Elsevier.
A full digitization of the copy owned by the University of Michigan is available from GoogleBooks.
Index to Mathematical Treasures