Copy of the drawing representing Galileo's idea of the application of the pendulum to the clock, 1659.

This copy of a drawing made by Galileo's (1564-1642) friend and biographer, Viviani (1622-1703) shows the incomplete pendulum clock, which Galileo designed just before his death. It represents the first known attempt to apply a pendulum to control the rate of a clock. Galileo had observed that the time taken for a pendulum to complete one swing was almost independent of the arc through which it swung and he had used a freely swinging pendulum to time various astronomical events. He recognised the potential of using a pendulum to control a clock but died before his work could be completed. It was Huygens (1629-1693) in The Hague, Holland, who eventually built the first successful pendulum clock in 1656.