It was most (allegedly) famously used by the Greek philospher Archimedes when he observed the increase in the height of his bathwater as he got into the bath and derived the principles determining the volume of an irregular object by its displacement (he was ordered to devise a way of determining the purity of the king's gold crown without damaging it)
He then supposedly ran naked down the street shouting "Eurika!" but the whole story (other than him discovering the principle somehow) is likely to be apocryphal.