BRAHM, William Gerard de (1717-1799). The Atlantic Pilot. London: Printed for the Author by T. Spilsbury, 1772. 8o (202 x 123 mm). Folding table (strengthened along fold on verso), 3 engraved folding maps (a few small splits along folds, the first slightly frayed along edges). Contemporary mottled calf (skilfully rebacked); quarter calf folding case. Provenance: red ink stamp number "287" on title. "PIONEER ATTEMPT TO EXAMINE THE SOURCE AND NATURE OF THE GULF STREAM" (Cumming) FIRST EDITION. The maps comprise "The Ancient Tegesta, now Promontory of East Florida," "Chart of the South End of East Florida, and Martiers," and "Hydrographical Map of the Atlantic Ocean, Extending from the Southernmost part of North America to Europe." The German De Brahm, who had been Captain of Engineers under the Emperor Charles VI, became one of the most skilled and prolific mapmakers in the Southeastern colonies; he was Surveyor General of the Southern District of North America from 1765 to 1771. This very rare pilots' guide was a "pioneer attempt to examine the source and nature of the gulf stream" (Cumming, British Maps of Colonial America, p.52), based on his observations during his 18-week expedition in 1765 along the Florida coast and in the Gulf of Mexico, and during his crossing to England in 1771. De Brahm's investigations into the Gulf Stream thus predate Benjamin Franklin's work on the subject, the latter having at about the same time caused all known data on the current to be engraved on a commonly used chart of the Atlantic -- but only later copies of Franklin's chart are known, dated 1786 and 1789. "[De Brahm's] studies, indeed, were carried further than his published work indicates, for one of the two unpublished De Brahm manuscripts now in the Harvard College Library is a continuation of the printed Atlantic Pilot, an extensive addition, with two manuscript charts, to his earlier investigations of the course and rate of flow of the Gulf Stream" (Lawrence Wroth, Some American Contributions to the Art of Navigation, Providence, 1947, p.29). VERY RARE: according to American Book Prices Current, only two copies have sold at auction since at least 1955: the Pierre S. duPont III copy (sold Christie's New York, 8 October 1991, lot 85) and the Frank S. Streeter copy (sold Christie's New York, 16 April 2007, lot 67). NUC cites one copy, at LC. JCB (3) II:1821; Sabin 7324 (citing the title incorrectly).