Editing Terrella (section)

==William Gilbert's terrella==
[[Image:Terrella3452.png|thumb|left|William Gilbert's terrella]]
[[William Gilbert (astronomer)|William Gilbert]], the [[Royal College of Physicians|royal physician]] to [[Queen Elizabeth I]],  devoted much of his time, energy and resources to the study of the [[Earth's magnetic field|Earth's magnetism]]. It had been known for centuries that a freely suspended [[compass]] needle pointed north. Earlier investigators (including [[Christopher Columbus]]) found that direction deviated somewhat from true north, and [[Robert Norman]] showed the force on the needle was not horizontal but slanted into the Earth.

William Gilbert's explanation was that the Earth itself was a giant magnet, and he demonstrated this by creating a scale model of the magnetic Earth, a "terrella", a sphere formed out of a [[lodestone]]. Passing a small compass over the terrella, Gilbert demonstrated that a horizontal compass would point towards the magnetic pole, while a [[dip circle|dip needle]], balanced on a horizontal axis perpendicular to the magnetic one, indicated the proper "magnetic inclination" between the magnetic force and the horizontal direction. Gilbert later reported his findings in [[De Magnete|De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure]], published in 1600.