Two papers on imaginary numbers: "Mémoire sur les quantités imaginaires" [AND] "The application of a method of differences to the species of series whose sums are obtained by Mr. Landen, by the help of impossible quantities".

London, The Royal Society, 1806. Two papers in one. Large 4to (29.2 x 23.0 cm). 114 [66, 48] pp. Original blind blue wrappers. = These two papers on imaginary numbers were both published in the same issue of Philosophical Transactions of the Royal Society of London. The first, by the French mathematician, mineralogist and theologian Adrien-Quentin Buée (1748-1826), who lived in exile in England, the second by the British mathematician Bejamin Gompertz (1779-1865), communicated by the Astronomer Royal, Nevil Maskelyne. Gompertz is best known for his "Law of Human Mortality" (published 1825), a demographic model used by actuaries and insurance companies. Buée fled France in 1792, during the Reign of Terror, and devoted his time to mathematical crystallography and to pure mathematics. According to Wikipedia "Ce n'est qu'à partir du xixe siècle que se développe l'aspect géométrique des nombres complexes, vus comme des éléments ou des transformations du plan, sous l'impulsion de l'abbé Buée et de Jean-Robert Argand (plan d'Argand), puis avec les travaux de Gauss et de Cauchy". This is the entire "Phil. Trans." for the year 1806, part I, and includes the Errata in the Memoir on Imaginary Quantities [on p. vi]. Another important contribution published in this part is William Herschel's astronomical work, On the Quantity and Velocity of the Solar Motion [pp. 205-237; six plates]. Uncut. Spine soiled, internally mostly clean, though plates a bit unevenly toned. Unmarked. Rare in this state.