Huygens, Christiaan, 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).