This story tells how he uncovered an attempt to cheat King Hieron.
The king ordered a golden crown and gave the crown’s maker the exact amount of gold needed. The maker delivered a crown of the required weight, but Hieron suspected that some silver had been used instead of gold. He asked Archimedes to think about the matter. One day Archimedes was considering it while he was getting into a bathtub. He noticed that the amount of water overflowing the tub was proportional to the amount of his body that was being covered by water. This gave him an idea for solving the problem of the crown. He was so thrilled that he ran naked through the streets shouting, “Eureka!” (“I have discovered!”).
There are several ways Archimedes may have determined the amount of silver in the crown. One likely method relies on an idea that is now called Archimedes’s principle. It states that a body immersed in a fluid is buoyed up (pushed up) by a force that is equal to the weight of fluid that is displaced (pushed out of place) by the body. Using this method, he would have first taken two equal weights of gold and silver and compared their weights when immersed in water. Next he would have compared the weight of the crown and an equal weight of pure silver in water in the same way. The difference between these two comparisons would indicate that the crown was not pure gold.