What do "Crystal Balls" really do?

They're supposed to make the fortune teller see into the future. They really do no such thing, because the fortune teller often asks questions or engages in a conversation and gets the information about the person without them being aware of it. There's an article on Wilpedia, http://en.wikipedia.org/wiki/Crystal_ball that will give you more information, It says it was invented by the Druids, but i thought it was the Gypsies who brought it over.