Huygens publishes 'De Ratiociniis in Ludo Aleae' ('On Reasoning in Games of Chance'), one of the earliest systematic treatments of probability theory. It establishes fundamental concepts in probability and mathematical expectation.

Huygens patents the pendulum clock, a revolutionary invention that significantly improves timekeeping accuracy. The clock is instrumental in navigation and scientific experiments.

Huygens publishes 'Horologium', a detailed description of the pendulum clock and his mathematical analysis of its motion. This work establishes his reputation as a leading physicist.

Huygens travels to England and becomes a founding member of the Royal Society of London, connecting with other leading scientists of his time.

Huygens publishes 'Horologium Oscillatorium sive de motu pendulorum ad horologia aptato demonstrationes geometricae' ('The Pendulum Clock or Geometrical Demonstrations Concerning the Motion of Pendula as Applied to Clocks'), a masterpiece of mechanics that explores the properties of pendulums and their application in timekeeping. It also includes theorems related to the tautochrone and brachistochrone problems.

Huygens writes 'Traité de la Lumière' ('Treatise on Light'), where he proposes the wave theory of light, explaining optical phenomena through wave propagation. Though completed in 1678, it was not published until 1690.