William Gilbert

The north-south pointing property of the compass needle was discovered in China around the year 1000, and in 1600 William Gilbert in London showed that this could be explained if the entire Earth was a huge magnet. As a model for the magnetic Earth he used a spherical magnet, which he called "terrella", the "little Earth." He moved a small compass over the surface of the terrella and demonstrated that it always pointed towards its magnetic poles.

In the 1830s a world-wide network of magnetic observatories was set up and it was then realized that disturbances of the compass needle, which were occasionally noticed, occured on a world wide pattern. They seemed to come from outside the Earth, and Alexander von Humboldt named them magnetic storms

In 1959 Thomas Gold of Cornell University proposed to name that environment "magnetosphere", and this name is still used.

Further Reading:

• look up in an encyclopaedia "magnetosphere", "Gilbert, William Gilbert", "Humboldt, Alexander von".

• William Gilberts book "De Magnete" ("On the Magnet"), originally in Latin, is available in two English translations one of them (by Dover books) still in print. See
  The Great Magnet, the Earth"

• Historical details and many references can be found in "A Brief History of Magnetospheric Physics Before the Spaceflight Era" by David P. Stern, Reviews of Geophysics, 27, 103-114, 1989.