Caption:
Joseph Louis Gay-Lussac and Jean-Baptiste Biot performing physics experiments in a balloon at 4,000 meters altitude, 1804. Woodblock engraving by E. Deschamps after Mes from Louis Figuier's "Les Merveilles de la Science: Aerostats" (Marvels of Science: Air Balloons), Furne, Jouvet et Cie, Paris, 1868.