Illustration from 'De Magnete' by William Gilbert, 1600.
© Science Museum / Science & Society Picture Library
Illustration showing an instrument for measuring declination, the angular deviation of a compas needle from due north. 'De Magnete' is an early work on magnetism by William Gilbert (1540-1603), published in 1600, subtitled, 'of magnets, magnetism and bodies, and of the magnetism of the Earth', containing 'many arguments and demonstrated experiments'. Gilbert (1544-1603) was an early investigator of magnetic and electrical phenomena and physician to Elizabeth I and James I.