Neuchatel; Geneva: Samuel Fauche; Barde, Manget & Co., 1783; 1788. 2 vols. 8vo. xii, 524 pp., including half-title; , 84 pp. FIRST EDITIONS. I: With folding tables and engravings, title vignette, headpieces. Library stamp on title; II: marbled paper, foxing throughout. Item #2380
First editions of both works. Saussure (1740-99) conducted extensive investigations on the vapor pressure of water at various temperatures, using human hair as a hygrometric element. His four Essais contain the results of his demonstrations, including the famous experiment on the role of water vapor in the atmosphere. In the Défense, Saussure remarks that the only physicists who had attacked his Essais were inventors of hygrometers that differed from his. Time has proven the accuracy of Saussure's statements. Many of Saussure's scientific instruments became the founding collection of the Musée d'Histoire des Sciences de Genève when that museum opened its doors on 24 June 1964.