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Alexander von Humboldt (1769-1859), German naturalist and geographer. At 27, Humboldt inherited enough money to plan an expedition with botanist Aime Bonpland to South America. They mapped over 2700 kilometres of the Orinoco River, catalogued huge tracts of flora and fauna and discovered and measured the Peruvian Current (now called the Humboldt Current). Returning to Europe, he studied the meteorology of Russia and drew the first isotherm map. From 1845 he published the five-volume work 'Kosmos', a summary of everything then known about the Earth. This 1859 portrait is by German artist Julius Schrader. (KEYSTONE/SCIENCE PHOTO LIBRARY/METROPOLITAN MUSEUM OF ART/SCIENCE PHOTO LIBRARY)