Late in the winter of 1665, an ailing Christiaan Huygens (1629–1695) was confined to his room for a few days. The Dutch physicist whiled away the hours of his confinement by closely observing and pondering the odd behavior of two pendulum clocks he had recently constructed. Huygens had obtained a patent on the first pendulum clock in 1656.
Huygens noticed that the pendulums of the two suspended clocks, hanging side by side from a common support, were swinging together. When one pendulum swung to the left, the other went to the right. The pendulums remained precisely in opposite phase for as long as he cared to watch.
His curiosity piqued, Huygens began to experiment. He deliberately disturbed the motion of one pendulum so that it no longer mirrored the other's movement