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HALLEY, EDMOND (1656-1743). Nova & accuratissima totius terrarum orbis Tabula Nautica variationum magneticarum index juxta observationes anno 1700 habitas constructa . Amsterdam: R. & I. Ottens, [c.1730].
HALLEY, EDMOND (1656-1743). Nova & accuratissima totius terrarum orbis Tabula Nautica variationum magneticarum index juxta observationes anno 1700 habitas constructa . Amsterdam: R. & I. Ottens, [c.1730]. Hand-coloured engraved map of the world, on 3 sheets joined, overall 530 x 1460mm, on the Mercator projection, the Americas at centre, with the Australian continent repeated at East and West, inset map of the North Polar regions. Contemporary outline and wash colouring. (Split in half along vertical fold with irregular tear at head, but without loss, old repairs to verso with some associated browning to recto, 90mm closed tear with repair to verso to North Atlantic affecting only one letter, edges strengthened to verso with old paper, the whole with even faint browning and minor spotting.) A fine example of the Ottens issue of Halley's isogonic world chart. First published separately in 1702 by Mount and Page, the chart was copied by Pieter Mortier soon after, followed by the present edition by the map publishers Reinier and Josua Ottens, who included it in their 1745 edition of Louis Renard's maritime atlas and other publications. One of Halley's important scientific contributions was his theory of terrestrial magnetism, in which he attempted to explain the variations in magnetic variations recorded on the earth's surface by postulating the existence of four magnetic poles. Between 1698 and 1700 Halley crossed the Atlantic as captain of the ship Paramore, charting magnetic variation in hopes of using the information to determine longitude at sea. Although this proved unsuccessful, he published two innovative charts in 1701 and 1702, the first of the Atlantic Ocean, the second the present world chart. These were the first published charts to indicate isogonic lines, or lines of equal magnetic variation in the oceans (called 'Halleyan lines' by contemporaries). 'Thus the isoline, or lines of equal [magnetic] value, was invented. For more than a century Halley's magnetic lines were a familiar feature of the world chart' (Shirley, p. xiv). Cf. Koeman III, p. 87, no. 15, and IV, Ren 3, map 4; The World Encompassed . 200; N.J.W. Thrower, 'Edmond Halley and thematic Geo-Cartography,' in The Compleat Plattmaker (Berkeley 1978), cf. pp. 215-218.