Four Unpublished Letters from Nicolas Fatio de Duillier to Isaac Newton

This article analyses four unpublished draft letters from Nicolas Fatio de Duiller to Isaac Newton, dating from June to August 1693, and held in the Special Collections in the Universiteitsbibliotheek in Leiden. Overall, these letters enrich our knowledge of Fatio-Newton’s alchemical correspondence in June 1693, a phase which likely represents the peak of the two natural philosophers’ alchemical collaboration. By scrutinising the content of the letters, and situating them in relation to primary and secondary sources, the article will place Newton and Fatio’s epistolary exchange in relation to the social and historical background of late seventeenth-century London, bringing to light so far undisclosed aspects of the networks, alchemical practices, and expertise of the two natural philosophers.