Dutch mathematician, astronomer, physicist, probabilist and horologist. His 1673 scientific masterpiece was Horologium Oscillatorium, a treatise on the mathematical theory and applications of the isochronous pendulum clock, which led to improved accuracy in the measurement of time. He is also noted for his opposition to the Newtonian corpuscular theory of light, providing a longitudinal wave theory which hypothesized propagation by spherical waves emitted along a wave front.