Revisiting Isaac Newton’s Index Chemicus: A Response to Richard S. Westfall

Previous attempts to date the five editions of Isaac Newton’s Index Chemicus found in Keynes MS 30 (King’s College Library, Cambridge University) have relied on an incomplete examination of the citations Newton provides for his references. This study shows that a full examination of all Newton’s citations provides a more accurate method of dating, and thus pushes the timeline of production for all versions forward several years from the early 1680s to the early 1690s. It also proves that authors previously thought to be unimportant to Newton’s late alchemical writings, such as Robert Boyle, played a larger role than once recognised. Finally, Newton’s use of a text received from Fatio de Duillier for the later versions of the Index Chemicus suggests that the final versions may have been the product of a collaboration between the two.