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1783: the year of the first experiments with air buoyancy, those of the Montgolfier brothers and of Pilâtre de Rozier. But 1783 is witness to other events in the sky. The best known is that of the eruption of the Laki volcano in Iceland, with its disastrous meteorological consequences and their effects on harvests in Europe, without a link being established at the time between these events. 1783 is also the year Lavoisier published his Réflexions sur le phlogistique (Reflections on Phlogiston) which ended the idea of a universe founded on four the elements. The simultaneist perspective, if one considers the year 1783 as a turning point, leads to seeing the sky as the locus of new experiments, but also as the laboratory for a new vision of the worls which if not global is at any rate more universal. The stakes are, a few years before the Revolution, the end of any credibility for theories inherited from Antiquity and specifically Aristotle, and the start of a chaotic but “connected” world.