Archimedes' principle states that any body completely or partially submerged in a fluid is acted upon by an upward force which is equal to the weight of the fluid displaced by the body.
Details of Archimede's Principle
Archimede's Principle, the first theorum of Buoyancy was published by Archimedes of Syracuse, Sicily. Archimedes was a man with great passion for math and sciences and lived from 287 B.C.E. to 212 B.C.E. This famous principle explaining the weight of a body immersed in liquid was published in his two book collection, entitled On Floating Bodies. The books also discussed the stability of various bodies of different shapes and different specific gravities.
Fun fact about Archimedes: Whenever a principle occured to him as he stepped into his bath, he was famous for saying "EUREKA" or " I have found it!"
A website devoted to Archimedes: