Magnetic dip and latitude. Page from 'De Magnete' (On the Magnet, 1600) by English physicist William Gilbert (1544-1603). This diagram was provided by Gilbert as a means of using a magnet to determine latitude without any need to see the Sun or stars. His experiments with a terrella ('small Earth', magnetised sphere) had shown that the magnetic dip of a needle depended on latitude. '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 folio is from between pages 200 and 201, chapter 8, book 5.