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Alexander von Humboldt (1769-1859), German naturalist and geographer, shown in his study. Humbolt was born at Berlin into a military family. 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. He died at Berlin, two years after suffering a stroke. (KEYSTONE/SCIENCE PHOTO LIBRARY/ROYAL INSTITUTION OF GREAT BRITAIN / SCIENCE PHOTO LIBRARY)