World, Isotherms (temperature), 1850.

"Humboldt's System of Isothermal Lines, or lines of equal Annual Mean Temperature over the Globe ..." engraved by W. & A.K. Johnston, published by William Blackwood & Sons in Johnston's Physical Atlas of Natural Phenomena, 1850. Steel engraved map with original hand colour, on thick paper. Good condition with plate mark and wide margins. Size 26.5 x 20.5 cms. Ref F717