SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Diagram of the Earth's magnetic field. Engraving showing the dip of the Earth's magnetic field at various latitudes, after the work of William Gilbert (1540-1603). In this picture, line AB is the equator, C is the North Magnetic Pole (Arctic) and D the South Magnetic Pole (Antarctic). The tip of the arrows are magnetic south, and the direction of the arrows indicates the direction a freely-rotating compass would point. To test the hypothesis, Gilbert used a special round lodestone called a terrela.
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