Gilbert on magnetic dip. Page from 'De Magnete' (On the Magnet, 1600) by English physicist William Gilbert (1544-1603). The diagram shows an experiment with his terrella ('little Earth', a magnetised sphere), showing the rotation and magnetic dip at a latitude of 50 degrees north. 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. 'De Magnete' reported Gilbert's studies of magnetism and electricity. He theorised that the two forces were closely related. He also considered the Earth to be a spherical magnet. This first edition of 'De Magnete' consisted of 115 chapters in six books and 246 pages. This is page 190, chapter 2, book 5.