HALLEY, EDMUND

Engraved chart (612 x 696 mm) flanked by letterpress instructions sheets affixed vertically to either side of chart, title cartouche over South America, secondary cartouche over Africa with dedication to William III. Creases where previously folded, several small paper repairs. As issued. 

Louis A. Bauer. "Some Bibliographical Discoveries in Terrestrial Magnetism," Nature 52 (1895) pp 79-80; "Edmund Halley and Thematic Geo-Cartography" In: The Compleat Plattmaker; Robinson. Marine Cartography in Britain,  pp 117-11; Tooley. Maps and Map-Makers, p 55; The World Encompassed, 199

APPARENT FIRST EDITION OF HALLEY'S FAMED ISOGONIC CHART, WITH RARE EARLY ISSUE OF INSTRUCTIONAL TEXT; "AMONG THE RAREST OF CARTOGRAPHICAL TREASURES" (Tooley). 

An instrument of singular importance for navigation in the North and South Atlantic, of which few examples have survived. While Halley is perhaps best known for his computation of the orbit of Halley's comet, his theory of terrestrial magnetism is one of his most important scientific achievements. Between 1698 and 1700, Halley sailed across the Atlantic in the ship Paramour charting magnetic variation. By postulating the existence of four magnetic poles, Halley hoped to explain the magnetic variations recorded on the Earth's surface. He published two charts during his voyage on the Paramour, a meteorological chart in 1701, and the present magnetic chart in 1701/1702. The two were the first published charts with lines of equal magnetic variation in the oceans; these were referred to as "Halleyan lines" by his contemporaries, and are now known as Isogonic lines. "Thus the isoline, or lines of equal value, was invented. For more than a century Halley's magnetic lines were a familiar feature of the world chart (Shirley, p. xiv). Instrument, rather than chart, is the best designation for this early issue, for which the printed text provides instructions on use. Throughout the 18th century, the Mount & Page partnership and imprint went through numerous permutations. Robinson dates that of "R. and W. Mount, and T. Page" to 1712. An inspired work of science by one of the great astronomers of the age, which went on to be re-printed numerous times through the 18th century, including in numerous editions of The English Pilot.