Rotating Poles, Shifting Angles and the Use of Geometry (Bond's Longitude Found and Hobbes' confutation)

In The Sea-Mans Kalendar (1636 [1638?]), Henry Bond predicted that magnetic declination would be 0 degrees in 1657, and would then increase westerly for (at least) 30 years. Based on these predictions, Bond went on to claim in The Longitude Found (1676) that, by using his model of magnetism, he can offer a technique for determining longitude. This paper offers an assessment of Bond's method for longitude determination and critically evaluates Thomas Hobbes's so-far neglected response to Bond's proposal in Decameron physio-logicum (1678), in which Hobbes complains about what he takes to be Bond's implicit natural philosophy and about his use of spherical trigonometry.