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First edition, first issue of Foucault's two combined reports of his famous mechanical demonstration of the rotation of the earth, the first of which originally appeared in vol. 32 of the Comptes rendus of the French Academy of Sciences (3rd February 1851 session) and the second in vol. 35 (27th September 1852 session); a second issue with a few minor corrections appeared not much later. Foucault's earliest experiment was private, but he repeated it in front of a fashionable audience in 1851, proving the rotation of the earth by means of a swinging heavy metal ball suspended from the dome of the Pantheon, "Foucault's pendulum". In 1852 Foucault refined the visible demonstration by his invention of the gyroscope. Extremely rare.