November 1996 Pierre Beaudry Baltimore MD. More non-Newtonian/Cartesian science for smarties. In 1656, Christiaan Huygens built the world's first pendulum clock. It was far more reliable than any previous mechanical timepiece based on his investigation into the nature of cycloids. For nearly 300 years, the most accurate clocks in the world all used pendulums. Huygens was the first to discover the principle of least time in light propagation by demonstrating that when a ray of light goes through two different media, "the times of passage of light taken together is the shortest that can be." (Christian Huygens, Treatise on Light.)"