ASTRONOMY. Correspondence addressed to François-Auguste CLAUDE (Strasbourg 1858-1938), astronomer, calculator at the Bureau des Longitudes. Most date from 1911. Envelopes preserved. - Maurice CORTIER (1879-1914), explorer. 6 autograph letters signed (one incomplete), 16 pp. in-8. Very interesting correspondence, several written from Gao (Niger) including statements of observations. + 4 drafts of replies. - Henri ROCQUES-DESVALLÉES (1854-1929), astronomer, calculator at the Bureau des Longitudes. Autograph letter signed, 3 pp. in-8, including 2 pages of calculations. - Émile RABIOULLE (1887-1914), astronomer at the Paris Observatory then in Toulouse and Algiers. 2 autograph letters signed. 5 pp. in-8 and in-12. Letters devoted to his calculations for the observation of stars. - Eugène COSSERAT (1866-1931), mathematician and astronomer. Autograph letter signed + 2 from his brother François. About an astrolabe for the Toulouse Observatory. - 2 other unidentified letters.