Horologium Oscillatorium : sive de motv pendvlorvm ad horologia aptato
Christiaan Huygens(1629-1695)
 Huygens was the only scientist to match Newton in versatility and originality in the seventeenth century. He was highly gifted in mathematics and achieved many important contributions in astronomy and physics. He improved the telescope and observed Saturn, Mars and other celestial bodies, discovered the rings of Saturn, Mars and the satellite Titan which was consequently named by him. Huygens realized the necessity of accurate time measurement, as a means to improve the precision of astronomical observation. It was also necessary for the exact determination of longitude on the sea. In order to invent a chronometer, Huygens followed Galileo and studied the mechanism of the pendulum clock and the mathematical analysis of the pendulum’s oscillation.
 In the above work, Huygens accumulated the entire results of this study, however only half of this book dealt with the clock itself. All the rest was devoted to new knowledge about dynamics. Huygens discovered that a precise isochronous pendulum must generate cycloidal locus, and devised a pendulum in which the pendulum cord oscillated between two cycloidal side plates. It was devised on the basis of a theorem that an involute of cycloid is also a congruent cycloid.
 Huygens developed further studies of the pendulum. He studied the fall of bodies along curves and derived studies about the moment of inertia, the force of gravity. At the end of this book, Huygens described thirteen theorems which are concerned with the theory of centrifugal force in circular motion. Huygens presented a copy of this book to Newton who acknowledged that his theory of universal gravitation had been influenced by Huygens’s theory of centrifugal force. This work was the greatest book on dynamics since Galileo’s “Discorsi.”