Newton acknowledged Wren, Hooke and Halley in this connection in the Scholium to Proposition 4 in Book 1 (in all editions): See for example the 1729 English translation of the Principia, at page 66.
In a letter to Edmund Halley dated 20 June 1686, Newton wrote: "Bullialdus wrote that all force respecting ye Sun as its center & depending on matter must be reciprocally in a duplicate ratio of ye distance from ye center." See: I. Bernard Cohen and George E. Smith, ed.s, The Cambridge Companion to Newton (Cambridge, England: Cambridge University Press, 2002), page 204.
digitale-sammlungen.de
daten.digitale-sammlungen.de
Johannes Kepler, Ad Vitellionem Paralipomena, quibus astronomiae pars optica traditur (Frankfurt, (Germany): Claude de Marne & heir Jean Aubry, 1604), page 10.
Translation of the Latin quote from Bullialdus' 'Astronomia Philolaica' … is from: O'Connor, John J. and Roberson, Edmund F. (2006) "Ismael Boulliau"Archived 30 November 2016 at the Wayback Machine, The MacTutor History of Mathematics Archive, School of Mathematics and Statistics, University of Saint Andrews, Scotland.
web.archive.org
Translation of the Latin quote from Bullialdus' 'Astronomia Philolaica' … is from: O'Connor, John J. and Roberson, Edmund F. (2006) "Ismael Boulliau"Archived 30 November 2016 at the Wayback Machine, The MacTutor History of Mathematics Archive, School of Mathematics and Statistics, University of Saint Andrews, Scotland.
wisc.edu
digicoll.library.wisc.edu
Robert Hooke, Micrographia … (London, England: John Martyn, 1667), page 227: "[I say a Cylinder, not a piece of a Cone, because, as I may elsewhere shew in the Explication of Gravity, that triplicate proportion of the shels of a Sphere, to their respective diameters, I suppose to be removed in this case by the decrease of the power of Gravity.]"
