Eureka

Meaning "I have found it!", it is Derived from the Greek word "heureka". Legend has it that Archimedes made this exclaimation when he noticed that objects placed in water displace an amount equal to their own amount. He then used this discovery to solve the problem of measuring the true gold content King Hiero's crown, which was a task that he was asked to perform.

This was emailed from a site visitor:
Archimedes is credited with the original use of the word eureka ( "heureka" ). This is accurate, but I feel it is worth mentioning more about the circumstances of his discovery. Here is the legend as I have heard it told:

King Hiero had just commissioned a new crown made, but suspected that it might not be pure, and that the craftsman who made it had cheated him. Hiero contacted Archimedes, a man known well educated(by the standards of the time). The king wanted to know how to determine the purity of the crown without damaging it, and Archimedes was at a loss. He did not know how to proceed, and went home deep in thought. Eventually, he went to take a bath. The tub was very full, and when he attempted to sit down, water spilled over the side. At this point, he realized the now well known principles of water displacement. It is said that in his excitement and eagerness to tell the king , he ran naked through the streets shouting "eureka! eureka!" (来源：EnglishCN英语问答中心[e问e答])

I have always found the details funny. though I cannot confirm, off the top of my head, that the running naked is true, it should amuse site visitors...