Huygens, Christiaan (krĭsˈtyän hoiˈgəns) [key], 1629–95, Dutch mathematician and physicist; son of Constantijn Huygens. He improved telescopic lenses and discovered (1655) a satellite of Saturn and studied the rings of Saturn. His findings were described in his Systema Saturnium (1659). He was the first to use the pendulum in clocks. He developed a wave theory of light opposed to the corpuscular theory of Newton and formulated Huygens's principle, which holds that, concerning light waves, every point on a wave front is itself a source of new waves. In 1678 he discovered the polarization of light by double refraction in calcite. His chief work is Horologium oscillatorium (1673).
See his Oeuvres complètes (22 vol. in 23, 1888–1950); study by A. E. Bell (1947); A. Elzinga, On a Research Program in Early Modern Physics (1972).