This site features a biography on William Gilbert. If you click on magnetism, you will find an indepth explanation of magnetism including magnetic poles and forces and fields. An outline of the basis of magnetism is included along with many other explanations which involve Gilbert's work. There are plenty of other words to click on through out the search to give you a clearer picture of one concept and supplies a neverending library of information on basic magnetism.
An biography of William Gilbert and his discoveries in magnetism.
This site shows the similarities and differences between the magnetic field around a bar magnet and the Earth's magnetosphere. It illustrates these concepts with pictures and small helpful explanations.