Ernest MOUCHEZ. Autograph manuscript signed, Alex. De Humboldt et Bonpland..., [ca. 1850]; folio of 23 pages plus title. Reading notes on the Astronomy part of Humboldt's voyage to America. Mouchez summarized the Astronomy part of Humboldt and Bonpland's Voyage aux régions équinoxiales du Nouveau Continent, volume I of the Recueil d'observations astronomiques, d'opérations trigonométriques et de mesures barométriques, which constitutes the 4th section of Humboldt and Bonpland's work (Paris, F. Schœll, 1810). His manuscript is in two parts: the first summarizes the Introduction, written by Humboldt, and the second summarizes the Preliminary Discourse, written by the astronomer Jabbo Oltmanns (1783-1833). The first part deals with the determination of positions using a repeating circle or a sextant, and then using reflective instruments. It is followed by remarks on the determination of geographical positions, on the proper motion of stars, on the determination of latitudes at sea by the meridian heights of stars, and on eclipses and their use to determine longitudes. The second part is devoted to the means used to determine the position of places: first the latitude (4 methods are presented), then the longitude (lunar distances; eclipses of the sun and occultation of stars; passage of the lower planets on the solar disk; right ascensions and hourly angles of the Moon). It is then discussed the methods of longitude not affected by parallax (eclipses of the Moon; satellites of Jupiter). Many scientists are mentioned in this study: Kepler, Gassendi, Peiresc, Newton, Bradley, Lalande, Bouguer, La Condamine, Arago, etc. A few annotations in pencil have been made in the margins by Mouchez during proofreading. An invitation card for the inauguration of the statue of Le Verrier at the Observatory, addressed to Henri Becquerel, is enclosed.