Herbert Butterfield on Robert Hooke

“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.”

“Hooke is amazing in the number, the variety and the ingenuity of his experiments as well as for his extraordinary fertility in hypothesis. He followed Bacon in his attempt to demonstrate that the effects of gravity on a body must diminish as the body was sunk into the bowels of the earth. He sought to discover how far the effects were altered at great heights or in the region of the equator; and he threw light on the problem by observations and experiments on the pendulum. From the globular shapes of the heavenly bodies and the stable conformations of the ridges on the moon he deduced that the moon and the planets had gravity; and by 1666 he saw the motion of a comet (for example) as incurvated by the pull of the sun... and suggested that the motion of the planets might be explicable on the kind of principles that account for the motion of a pendulum. In 1674 he was suggesting that by this route one could arrive at a mechanical system of the planets which would be "the true perfection of astronomy." He pointed out that... account must be taken of the force which all heavenly bodies must be presumed to be exerting on one another.”