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"Alexander von Humboldt (1769-1859), German naturalist and explorer. Humboldt trained as a mining engineer, and then used inherited money to indulge his knowledge of botany and geology. He began an epic exploration of central and south America during which time he amassed scientific specimens and observations. He studied ocean currents (the Humboldt Current is named in his honour); proposed the idea of the Panama Canal; introduced isobars and isotherms on weather maps; and discovered that the Earth's magnetic field decreases from poles to equator. His five volume Kosmos may be said to have founded the science of geophysics. Photograph published between 1855 and 1865." (KEYSTONE/SCIENCE PHOTO LIBRARY/LIBRARY OF CONGRESS/SCIENCE PHOTO LIBRARY)