A fine example of Adam and Charles Black's 1840 chart of the Magnetic Curves of equal Variation. The chart depicts the magnetic curves over the entire world, but does not show the isomagnetic lines over any continent except North America. It marks the North Magnetic Pole at the Boothia Felix (now the Boothia Peninsula) based on the first expedition by James Clark Ross in 1831. Due to the magnetic changes in the earth's core, the position of the magnetic poles keep changing over time. In 2005, it was estimated that the North Magnetic Pole is positioned to the west of ellesmere Island in Canada. This map was engraved by G. Aikman for issue in the 1840 edition of Black's General Atlas.
Charles and Adam Black (fl. 1807 - present) were map and book publishers based in Edinburgh. Charles and his uncle, Adam, both of Edinburgh, Scotland, founded their publishing firm in 1807. They published a series of maps and atlases throughout the 19th century. In addition to an array of atlases, the Black firm is known for their editions of the Encyclopedia Britannica (1817 - 1826) and the first publishing of Sir Walter Scott's novels in 1854. In 1889 the A. & C. Black publishing house moved to London where it remains in operation to this day.
Hall, Sydney, Black's General Atlas: A series of Fifty-Four Maps from the Latest and Most Authentic Sources, Engraved on Steel, In the First Style of the Art, (Edinburgh: Adam and Charles Black) 1840.
Very good. Blank on verso. Original platemark visible.
Rumsey 2305.006 (1854 edition). Philips (atlases) 4334.