"Heureka" is a Greek word meaning "I have found it!" and it
  was made famous by Sicilian philosopher Archimedes.
  Archimedes had been given the difficult task of determining
  whether a crown was truly pure gold or actually alloyed
  with an inferior metal.

  He was stumped until one day at the public baths he noticed
  his tub overflowing. Archimedes realized that objects of
  different density but equal weight displace different
  amounts of water when submerged. Since gold has a different
  density than other metals, this method would be successful
  in determining whether the crown was pure gold. Archimedes
  was so excited about the idea that he jumped out of the
  bath yelling "Heureka! Heureka!" and ran home naked to try
  the experiment!