BRAZIL. Gaston de ROQUEMAUREL (1804-1878) naval officer and explorer. Autograph manuscript, Plan de Rio Janeiro, par Mr Barral, 1826 et 27; 1page large in-fol. of a bifolium. On the method used by Barral to survey the coastline of Rio de Janeiro. The first step is to check Rochon's micrometer by means of a base and a micrometric yardstick. Then the astronomical bearings of the base and sea-level stations were determined. Once the contours of the roadstead are complete, the islets, rocks and main sounding points are surveyed. The next step is to explore the coast with a longboat and a pirogue, etc.Enclosed is another autograph manuscript (2 1/2 pages in-fol.), notes taken from John Ross's Relation du second voyage fait à la recherche d'un passage au nord-ouest pendant les années 1829 à 1833 (Paris, 1835).