Robert Hooke (1635 - 1703) postulated before Newton the theory of universal gravitation, but was unable to express it mathematically. He did moreover state the inverse square law and related this to the path of projectiles. He quarrelled constantly with Newton on the basis of who introduced these ideas first. He had made many inventions including an odometer; a hearing aid; a reflecting Quadrant; a system of telegraphy; a barometer; the universal joint; an anchor escapement for clocks and an arithmetical machine (calculator). He produced the Gregorian telescope and a theory of the variation of the compass. He explained the scintillation of the stars by irregular atmospheric retractions and inferred the solar repellent force in producing the tails of comets. He suggested the motion of the sun amongst the stars and propounded correct notions as to the nature of fossils and the succession of living things upon the earth (preceding Darwin). He also invented a marine barometer. One of his posthumous works was a hypothesis of the cause of gravity found in any propagated pulse of the ether (dark matter). See Dictionary of National Biography, 1893