The Great Magnet, the Earth

by David P. Stern

Commemorating the 400th anniversary of
"De Magnete" by William Gilbert of Colchester

    A Millennium of Geomagnetism, included here, first appeared 9/2002 in Rev. Geophys and covers the material in more technical detail "
    "Zipped" compressed version of this set (3 Mb) .
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      William Gilbert
    In 1600, four hundred years ago William Gilbert, later physician to Queen Elizabeth I of England, published his great study of magnetism, "De Magnete"--"On the Magnet". It gave the first rational explanation to the mysterious ability of the compass needle to point north-south: the Earth itself was magnetic. "De Magnete" opened the era of modern physics and astronomy and started a century marked by the great achievements of Galileo, Kepler, Newton and others.

    If you lived in London in 1600, you could have purchased "De Magnete" for seven shillings and sixpence. To read it, of course, you would have to know Latin, the language of science in 1600. You might have had the rare privilege of attending first runs of Shakespeare's plays in the "Globe" theatre--sitting in the balcony if you could afford it, standing in front of the stage if not. However, you might have had to weigh this pleasure against the peril of bubonic plague, which usually spread in the city during summer months.

This web site tells the story of Gilbert and his book--with glimpses of London in 1600, and with studies of magnetism before Gilbert. It then recounts the later history of the Earth's magnetism, including...
  • The remarkable discoveries of Halley, Coulomb, Oersted, Ampere and Gauss.
  • The unexpected connection between sunspot activity and the Earth's magnetism.
  • The deep-seated "'dynamo" believed to be responsible for the field.
  • The strange reversals of the Earth's magnetic polarity.
  • The role of magnetism in discovering the "drift" of continents.
  • The extension of magnetism to space around Earth, even to other planets.
One could hardly find a more striking story of grand adventure in science!

An Index to the Web Site

"A Millennium of Geomagnetism"

  1. Introduction
  2. Early discoveries
  3. William Gilbert
  4. Halley
  5. Coulomb
  6. Oersted and Ampere
  7. The Lodestone
  8. Gauss and Humboldt
  9. Explorations and Surveys
  10. Faraday's Lines of Force (field lines)
  11. Faraday's Disk Dynamo
  12. Sunspots
  13. The Dynamo Process on the Sun
  14. The Earth's Dynamo
  15. Dipole Reversals and Plate Tectonics
  16. Magnetic Storms and Ring Currents
  17. The Magnetosphere
  18. Magnetic Reconnection
  19. Planetary Magnetospheres
  20. Assessment

Of Special Interest to Science Teachers

"A Teacher's Introduction to the Earth's Magnetosphere" (illustrated talk)

Note: If you liked what you found here, you might want to look up other (much larger!) web sites by the same author, on magnetism in space and on spaceflight and astronomy:
            Happy Exploring!

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Author and Curator:   Dr. David P. Stern
     Mail to Dr.Stern:   earthmag("at" symbol)

Last updated 20 November 2003