Before 1687 Newton had published nothing about his laws of motion or gravity, though by 1673 he may have proved how the gravity of the sun pulled on the planets. Early in 1684 three Fellows of the Royal Society, Edmond Halley, Christopher Wren and Robert Hooke, discussed whether such a proof was possible. Visiting Newton in Cambridge later that year, Halley asked that he publish his theory, leading ultimately to the publication of the Principia in 1687. This copy of the first edition is Newton’s own, heavily annotated throughout by him with changes to be introduced into the second edition. The project of amending the first edition of the Principia began quite early during the 1690s. Together with other sources such as the annotated copy of the Principia from Newton’s Library (Trinity College, shelfmark NQ.16.200) and the Liber Secundus Add. 3990, allows scholars to obtain important information about Newton’s protracted reworking of the first edition. For example, at the start of Book 3 [p. 402], Newton had defined a number of ‘Hypotheses’ governing his approach to natural phenomenon. In revising the Principia, he developed these hypotheses into a set of rules: ‘Hypotheses’ was firmly crossed through and replaced with ‘Regulæ philosophandi’ (‘Rules of philosophising’). The book was severely damaged by fire and damp [pp. 347 ff.] some time before it was given to the Library in 1872 as part of the Portsmouth collection.