Earth as a magnet: geomagnetic field

What was discovered

Experimenting with a magnetised sphere (terrella), Gilbert showed that the Earth itself is a great magnet and that this explains the compass's orientation and magnetic dip. It was one of the first treatises of experimental physics.

Place of publication of 'De Magnete'. Gilbert wrongly attributed declination to the distribution of continents.

What it led to

• Geomagnetism and declination charts (Halley)
• Core dynamo theory
• Magnetic reversals and palaeomagnetism

Built on

• Chinese compass and its nautical use
• Petrus Peregrinus's observations (1269)

Made possible

• Geomagnetic reversals1906 / 1929 / 1963
• Dip compass
• Magnetometers

📄 Original publication

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