"By 1678 he had formulated the idea of gravitation as a universal principle; and by 1679 he, too, had discovered that the diminution of the force of gravity is proportional to the square of the distance. In this period it would appear that Newton... seemed to be less sure of his apprehension than Hooke. At the same time [Newton] was called upon for mathematical help... Hooke was to claim the priority in respect of the whole gravitational theory, and because Newton had been secretive about his work in 1665-66, because many of Hooke's own papers disappeared, and because Newton's memory was defective sometimes—or his accounts unreliable—the controversy... has been renewed in recent years. But... Hooke did not produce the mathematical demonstrations of his system. ...in the crucial period he was developing his mathematical powers more than was once imagined... His reputation has risen, with... research... though the glory of Newton has not been eclipsed."