Christian Huygens perhaps invented a pendulum clock. In 1665 he noticed that two or more pendulum clocks suspended on the same beam would, after a while, start to synchronize themselves. The clock-driven mechanism emanates energy in the form of acoustic waves that penetrate the beam and travels from one clock to the other. The magnitudes gradually converge, and eventually they synchronize, similar to the rythm of flashing of fireflies. Huygens supposed to be inspired by Comenius to construct the pendulum-driven pendulum clocks.