Archimedes' Principle of water displacement was discovered by a Greek mathematician, astronomer, engineer, inventor and all-around smarty-pants named, of course, Archimedes.
Tasked by his king to determine the authenticity of a gold crown—the king suspected he had gotten snookered by the royal goldsmith—Archimedes decided to take a bath and think about it.
Lowering himself into the tub, he noticed the water level rise. At this moment, Archimedes had what can only be called an a-ha moment. He realized—and I'm paraphrasing here—that a body submerged in fluid is subject to an upward force equal in magnitude to the weight of the fluid it displaces. Who knew?
Legend has it that he shouted "Eureka!" and ran naked through the streets of Syracuse, Sicily.
And so we tip our hats to Archimedes and his eponymous principle.