Eureka

"Eureka" comes from the Ancient Greek word εὕρηκα heúrēka, meaning "I have found (it)" It is an interjection used to celebrate a discovery or invention. It is a transliteration of an exclamation attributed to Ancient Greek mathematician and inventor Archimedes. He reportedly proclaimed "Eureka! Eureka!" after he had stepped into a bath and noticed that the water level rose. He suddenly understood that the volume of water displaced must be equal to the volume of the part of his body he had submerged. The volume of irregular objects could be measured with precision, a previously intractable problem. He is said to have leapt out of his bathtub and run through the streets of Syracuse naked.

Archimedes' insight led to the solution of the problem of measuring gold's purity. Hiero of Syracuse suspected, correctly, he had been cheated by a goldsmith removing gold and adding the same weight of silver to a crown he commissioned. Equipment for weighing objects with good precision already existed, and now that Archimedes could also measure volume, their ratio would give the object's density, an important indicator of purity. The answer was now a simple one ... balance the crown against pure gold in air, and then submerge the scale with crown and gold in water to see if they still balance.