This collection consists of a letter written, in French, by Colin Maclaurin, to Jean-Jacques d’Ortous de Mairan, Perpetual Secretary of the French Académie des Sciences. Maclaurin first discusses his major work, the Treatise of Fluxions (1742), a rigorous and systematic defence of Newtonian calculus. Maclaurin acknowledges that foreign readers might be surprised by his methodology but explains that he wished to meet potential scientific and philosophical objections from prominent British anti-Newtonians like Bishop Berkeley. Maclaurin goes on to enquires about a French geodetic expedition to Peru, sponsored by the Académie des Sciences, to establish whether the earth’s circumference was greater around the equator or around the poles. Finally, he reports on recent attempts to correct the geography of the North of Scotland and promises to send Mairan a newly engraved map of the country. Maclaurin believed that it was crucial to map the Scottish coastline accurately in view of a possible French-backed Jacobite invasion.