Robert Hooke

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Robert Hooke : biography

18 July 1635 – 3 March 1703

In 1686, when the first book of Newton’s ‘Principia’ was presented to the Royal Society, Hooke claimed that Newton had had from him the "notion" of "the rule of the decrease of Gravity, being reciprocally as the squares of the distances from the Center". At the same time (according to Edmond Halley’s contemporary report) Hooke agreed that "the Demonstration of the Curves generated therby" was wholly Newton’s.

A recent assessment about the early history of the inverse square law is that "by the late 1660s," the assumption of an "inverse proportion between gravity and the square of distance was rather common and had been advanced by a number of different people for different reasons".Gal, Ofer (2002) Meanest foundations and nobler superstructures: Hooke, Newton and the ‘Compounding of the Celestiall Motions of the Planetts, Springer, , ISBN 1402007329. Newton himself had shown in the 1660s that for planetary motion under a circular assumption, force in the radial direction had an inverse-square relation with distance from the center. Newton, faced in May 1686 with Hooke’s claim on the inverse square law, denied that Hooke was to be credited as author of the idea, giving reasons including the citation of prior work by others before Hooke. Newton also firmly claimed that even if it had happened that he had first heard of the inverse square proportion from Hooke, which it had not, he would still have some rights to it in view of his mathematical developments and demonstrations, which enabled observations to be relied on as evidence of its accuracy, while Hooke, without mathematical demonstrations and evidence in favour of the supposition, could only guess (according to Newton) that it was approximately valid "at great distances from the center".

On the other hand, Newton did accept and acknowledge, in all editions of the ‘Principia’, that Hooke (but not exclusively Hooke) had separately appreciated the inverse square law in the solar system. Newton acknowledged Wren, Hooke and Halley in this connection in the Scholium to Proposition 4 in Book 1.See for example the 1729 English translation of the ‘Principia’, . Newton also acknowledged to Halley that his correspondence with Hooke in 1679–80 had reawakened his dormant interest in astronomical matters, but that did not mean, according to Newton, that Hooke had told Newton anything new or original: "yet am I not beholden to him for any light into that business but only for the diversion he gave me from my other studies to think on these things & for his dogmaticalness in writing as if he had found the motion in the Ellipsis, which inclined me to try it."

One of the contrasts between the two men was that Newton was primarily a pioneer in mathematical analysis and its applications as well as optical experimentation, while Hooke was a creative experimenter of such great range, that it is not surprising to find that he left some of his ideas, such as those about gravitation, undeveloped. This in turn makes it understandable how in 1759, decades after the deaths of both Newton and Hooke, Alexis Clairaut, mathematical astronomer eminent in his own right in the field of gravitational studies, made his assessment after reviewing what Hooke had published on gravitation. "One must not think that this idea … of Hooke diminishes Newton’s glory", Clairaut wrote; "The example of Hooke" serves "to show what a distance there is between a truth that is glimpsed and a truth that is demonstrated".The second extract is quoted and translated in W.W. Rouse Ball, "An Essay on Newton’s ‘Principia’" (London and New York: Macmillan, 1893), at page 69.The original statements by Clairaut (in French) are found (with orthography here as in the original) in "Explication abregée du systême du monde, et explication des principaux phénomenes astronomiques tirée des Principes de M. Newton" (1759), at Introduction (section IX), page 6: "Il ne faut pas croire que cette idée … de Hook diminue la gloire de M. Newton", [and] "L’exemple de Hook" [serves] "à faire voir quelle distance il y a entre une vérité entrevue & une vérité démontrée".