For centuries, humanity believed magnetic mountains and garlic fumes dictated the behavior of compasses.
In short: Before modern science, the Earth's magnetic field was a profound mystery. Early thinkers blamed celestial poles, magnetic islands, or even the smell of onions for confusing compass needles. It took centuries of maritime struggle and experimental rigor to realize the planet itself is a giant, shifting magnet.
In classical antiquity, magnetism was often explained through metaphysical concepts like a 'life force' or invisible effluvia. Because compasses did not always point to true north, early navigators and scholars hypothesized that magnetic mountains—legendary landmasses near the poles—exerted a pull strong enough to hold ships in place or even rip iron nails from their hulls. This belief persisted in various forms until the sixteenth century, when cartographers like Gerardus Mercator attempted to map these mountains, only to find that their locations contradicted observational data.
The transition to a modern understanding began with William Gilbert, who published his landmark book De Magnete in 1600. Through experiments with a magnetized sphere he called a 'terella,' Gilbert deduced that the Earth acts as a large magnet. He dismissed the idea that surface topography, such as continents, caused magnetic deviations, though he incorrectly assumed the Earth's magnetic field was static. His work laid the foundation for the scientific study of geomagnetism, though his cosmological theories—which suggested magnetism kept the planets in motion—were eventually superseded by Newtonian gravity.
The assumption that the magnetic field was constant was shattered in 1635 when Henry Gellibrand confirmed that magnetic declination—the difference between magnetic and true north—changed over time. This discovery of secular variation sparked a new era of global monitoring. By the nineteenth century, scientists like Carl Friedrich Gauss and Alexander von Humboldt organized massive international campaigns to systematically survey the field. Today, we know the magnetic poles are in constant motion due to the liquid flow of the Earth's core, a phenomenon tracked by the World Magnetic Model, which is updated every five years by agencies like the British Geological Survey and NOAA.
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- Summary by Intellect · source: History of geomagnetism
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