In the history of physics, verticity (Latin: verticitate) is an alleged tendency to move around or toward the North or South Pole, often called Earth's "vertices".
In his acclaimed 1600 treatise On the Magnet and Magnetick Bodies, and on That Great Magnet the Earth, William Gilbert distinguished two species of verticity. Surface verticity, he said, is a tendency to point north found in ordinary "loadstones" and magnetised iron. This verticity was the weaker expression of a more powerful verticity—deep verticity—intrinsic to the Earth's core. Gilbert was among the first to believe that the Earth spins, and attributed this spinning to Earth's deep verticity. In his judgement, deep verticity also explained surface verticity: over time, bits and pieces of matter escaped from Earth's core, their verticity having been corrupted and weakened by exposure to the degraded matter of Earth's crust. These bits of matter became the variety of weak magnets found nearer the Earth's surface.
Gilbert's account of magnetism did not persuade Francis Bacon. He denied that Earth spun, and he denied deep verticity. Earth's core was cold, passive, and unmoving, as Telesio had said, and the Earth was not magnetic. Bacon offered an alternative explanation of magnetism. He construed magnetic motion as westward motion around Earth's vertices. Of course, such motion could be found everywhere. The Atlantic Ocean rolled westward and ricocheted off the eastern coast of the New World, creating the tides. The planets, stars, sun and moon migrated in the same direction. The stirrings of magnets could not be blamed on a special force, but only on the impulse of nearly all things to go west.
- William Gilbert, De magnete, London, 1600, pp. 10-11, 12, 173-176. (Cited in Rees 2006, p. liii)
- William Gilbert, De mundo nostro sublunari philosophia nova, Amsterdam, 1651, pp. 35-36, 46, 107-109. (Cited in Rees 2006, p. liii.)
- Graham Rees, ed. 2006. The Oxford Francis Bacon, VI: Philosophical Studies c. 1611-c. 1619. Oxford: Clarendon Press. ISBN 0-19-812290-X.
- Graham Rees, 1979. "Francis Bacon on Verticity and the Bowels of the Earth," Ambix (26), pp. 202-211.