Pierre-Simon de LAPLACE (1749-1827) astronomer and geometer. Autograph manuscript; 1 1/2 pages oblong in-4. Considerations on tides. This folio, with numerous erasures and corrections, as well as marginal additions, is an addition to one of his works; a note refers to Book XI of his Treatise on Celestial Mechanics. "I shall present here some considerations on sea level and its reductions. Let us imagine around the earth a very rare fluid everywhere of the same density, very low in elevation, but which nevertheless embraces the highest mountains: such would be more or less our atmosphere reduced to its average density"... Laplace describes the principle of what he calls "sea level", develops the notions of variation in gravity, centrifugal force, constants of the terrestrial sphere, the equator, etc.., assuming that the earth is "an ellipsoid of revolution partly covered by the sea", on which this density is exerted... Etc.