Answer:
Archimedes discovered density by sitting in a bath full of water, and realized the water that spilled out was how much space he took up in the bath. How many liters that spilled out was how many liters Archimedes took up in the world. As legend has it, when he found this out he ran into the street - naked - shouting "Eureka!" which means, in Greek, "I've found it!" He was shouting "Eureka" because the king asked him to find out if his crown was all gold or did the goldsmith take some gold and used silver instead.