In 1600, William Gilbert published his De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth). In this work he describes many of his experiments with his model earth called the terrella. From his experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses pointed north (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass).
Gravity and magnetism are thought not to be related. We are told magnetism is the effect of electric currents, and that gravity is the property of massive matter. Matter is light vibrating at very short wavelengths, and very high frequencies (it's frequency would also appear to determine its mass). If you brought together a lot of matter, say planet sized, I wonder what is the net effect of all these high frequencies ?
Only 30 km below the Earth's crust we find the mantle layer reaches a temperature of 1000 degrees c . As we journey down it gets hotter, and the molten rock more liquid. At the very centre of the planet, 5,200 km below the surface, we find an inner core of iron at 4,300 degrees c. The inner core is under such extreme pressure that it remains solid. The greater the pressure, the less room matter has to vibrate, and so the frequencies are getting higher and higher. However, 'electricity' is found at low frequencies- all the way at the other end of the electromagnetic spectrum.
It is said that the Earth cannot be a large permanent magnet since magnetic minerals lose their magnetism when they are hotter than about 500 degrees c. Almost all of the Earth is hotter, and the only way to make an electric field is with a circulating electric current. Light from the Sun takes 500 seconds to reach Earth; this can be written as a frequency of 0.002 Hz. This is an extremely, extremely low frequency when compared to the frequency at which matter oscillates - at billions and billions of times per second. Is light from the Sun acting as an electric current?
At the turn of the 19th century, there was a Norwegian experimenter and explorer called Birkeland. He knew that the Earth was a giant magnet. He wanted to understand the dynamics of the aurora borealis (northern lights). Birkeland led an expedition to the northernmost reaches of Norway to measure the Earth's magnetic field. He found that near the north pole, the magnetic field lines don't run along the earth's surface the way they do near the equator. Instead the field lines go almost straight up and down. The magnetic field flows into the south pole and out of the north pole.
In the true spirit of the times, he went home and built a model of what he found. The model was a sphere with a generated magnetic field, onto which electrically charged particles flew through a tube. The charged particles are pushed away from the equator, along the lines of force, and right into the north and south poles of the model. In nature, as the particles flow in to the upper polar atmosphere, they collide with atmosphere gases, generating the colourful light display of the aurora. Some might think that because this early experiment simulated the magnetic field, it fails to explain how the Earth generates it in the first place. But, on reflection, does it?
Many thanks -
http://en.wikipedia.org/wiki/Earth
http://www.news.wisc.edu/2515
http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html
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