Chart of the Curves of Equal Magnetic Variation, 1858...

Chart of the Curves of Equal Magnetic Variation, 1858...



Published 1859, London

Size: 26" x 39"

Condition: Very Good. Some restoration to blank margins, including a small filled hole and some sort closed tears.


A very rare and scientifically important nautical chart outlining the global magnetic variations of the mid 19th Century as trade became considerably more global in scope following the end of the Napoleonic wars.  The chart is highly relevant as it the first isogonic chart, issued by the British Admiralty and it has been argued that it is “by far the era’s best chart of its kind.”  This is the first edition of this highly influential chart that would be later updated in 1863, 1865, 1867 and 1871.  Isogonic charts are defined as charts connecting points on the earth’s surface at which the magnetic declination is the same.  In order to issue such a chart, the British Admiralty under the supervision of Master Frederick Evans, compiled data provided by different ship based and land based readings that emanated from numerous locations on the earth surface.  For example, the notations on the chart indicate that readings of the Arctic regions are from the observations of British and American explorers between 1818 and 1856. Those in the Russian Empire are from the observation of Baron Wrangel in 1821-3, as well as those of Erman, Hansteen and Due in 1828-9.  On the other hand, the approximate values in the Antarctic Oceans are from the observations made in the H.M. Ships Erebus and Terror by Captains Sir J.C. Ross and Crozier in 1840-3, and in H.M. Bark Pagoda, as well as from Lieutenants T.E. Moor and Clerk in 1845.
This nautical chart thus was highly important to ship navigation as economic trade increased the need for better and more detailed charts for merchants and navies alike who’s trade routes and geo-political interests in the mid 19th Century became global and reached all the far corners of the earth.  That being said, the Magnetic Pole, which attracts compasses as opposed to the true North Pole, has a tendency to move from year to year thus rendering the readings inaccurate as time progresses.  As such, the chart included an insert in the lower right hand quadrant that showed the annual change of the magnetic variations.
Evans, owing in large part to the success of this map as well as to other surveying work in the field, led to his being named to Hydrographer of the Royal Navy in 1874.