Gilbert on magnetic declination. Page from 'De Magnete' (On the Magnet, 1600) by English physicist William Gilbert (1544-1603). The diagrams show lines of meridian (top) and mountains on a terrella ('little Earth', a magnetised sphere, bottom), part of Gilbert's attempts to explain magnetic declination, where a compass needle does not point to true North. '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 157, chapter 2, book 4.