Chart of the curves of equal magnetic variation, 1858 [cartographic material] /

"The curves on the west coast of Africa between Cape Palmas and the Cape of Good Hope are chiefly from observations ... and inserted on this chart in 1861".; Chart "2598".; "Corrections to 1861, Dec. 63, Jan. 65".; Prime meridian: Greenwich.; Map originally published in 1859.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.map-rm3384. Inset: Index chart, shewing the approximate annual change of the magnetic variation for the epoch 1858