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Meteorological observations developped in the eighteenth century with the descriptions of physical cloud phenomena from Descartes to Pieter van Musschenbroek. The description in the Encyclopédie is unstable, dependent on the vocabulary of vapours and exhalations; “evaporation” analyses the cycle of water, “nuee” the mobility and colour of clouds. Meteorology becomes a privileged object of experimental physics, and of determinist thought in the Système de la nature of d’Holbach, inspired by the idea of the possible modelization of phenomena. This article explores the paths taken up by Diderot as a careful observer of cloud phenomena, and as a stroller sensitive to the pictorial values of clouds in the works of Vernet and Loutherbourg. Beyond the fine appreciation of the “art of elevating vapours on canvas” he ventured a use of metaphors which question the regime of certainty which ruled materialist thinking.