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Magnetic dip angle measurement by English physicist William Gilbert (1544-1603), 17th-century illustration. The diameter of the dial was 'six fingerlengths'. The instrument was made of wood and brass, with a steel needle magnetised by hand rubbing with a lodestone. Magnetic dip is the angle by which a compass needle dips compared to the horizontal, an angle that varies with location on the Earth's surface. Here, the compass dial is freely floating and has dipped to the left. This illustration was published in Gilbert's book 'De Magnete', first published in 1600. This picture was taken from the second edition reprinted in 1628.
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