Earth's Magnetism
Most ancient civilizations were aware of the magnetic phenomenon. Sailors in the late thirteenth century used magnetized needles floating in water as primitive compasses to find their way on the sea. However, most believed that the magnetization of the Earth came from the heavens, from the so called celestial spheres which Greeks invented. It was believed that the night sky is just a shell with small holes were the stars are visible and that beyond that shell was an amazing apparatus of instruments, amongst which magnets, that controlled lives of people on the surface of the Earth.
It was William Gilbert, an English physician, who was the first one to question the notions of magnetic heavens. He proposed that Earth itself was magnetic. Lodestones, naturally occurring magnetic magnetite (an ore of iron) were known at that time and he thought that Earth may be just a giant lodestone. He created a simple model to prove his point. He made a sphere of lodestone; he called it terrella, and then used a primitive compass on and around this sphere to investigate the phenomenon.
He noticed that the compass needle moved as expected, always pointing to the magnetic poles no matter where it was placed around the sphere. But only an intelligent scientist like himself could have noticed something else that was proof positive that the Earth’s magnetism comes from below and not above. The compass needle had a small horizontal declination or dipping towards the pole, and this dipping changed depending if the position of the compass was on the northern or southern hemisphere. When he removed his sphere the declination was still there, it did not change into an inclination or upward rise as it should have done if the magnets were truly above in the heavens. He published his findings in his book ‘De Magnete’ in 1600 and placed himself as one of history’s first true scientists and experimenters.
