Dutch physicist and astronomer Christiaan Huygens (1629-93), the inventor of the pendulum clock. The idea of using a pendulum to measure time had been proposed by Galileo (1564-1642) but he had not found how to keep one swinging. On Christmas Day 1656 Huygens designed a table clock that kept the pendulum swinging by means of a spring. He later made further advances in time-keeping. Huygens moved to France to work for Louis XIV during 1666-81 and published the results of his clock research in Horologium Oscillatorium (1673). Huygens also made advances in optics, astronomy, such as discovering the rings of Saturn, and mathematics. Colorized version of 9A8177.