Eureka, Eureka! (I found it, I found it!).

-Archimedes
Vitruvius 9.9.10.  Attributed, on discovering the principle of upthrust on a floating body while having a bath.  Archimedes had been given the task of establishing whether there was the proper weight of gold in the crown of Hieron of Syracuse. One day when entering his bath he noticed the water which flowed over the sides as he entered and he correctly perceived that the weight of the water displaced was that of the weight of his body.