I checked on google and I found some really good answers. The first link that came up was the yahoo answers. There are some excellent answers over there. Of course I could have copied and pasted it on here, but my answer would have been disapproved.
Here are the links:
answers.yahoo.com
answers.yahoo.com
or even try en.wikipedia.org
Here are the links:
answers.yahoo.com
answers.yahoo.com
or even try en.wikipedia.org