<P> The density of a material varies with temperature and pressure . This variation is typically small for solids and liquids but much greater for gases . Increasing the pressure on an object decreases the volume of the object and thus increases its density . Increasing the temperature of a substance (with a few exceptions) decreases its density by increasing its volume . In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid . This causes it to rise relative to more dense unheated material . </P> <P> The reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics . Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass . </P> <P> In a well - known but probably apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy . Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass; but the king did not approve of this . Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water . Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!" (Εύρηκα! Greek "I have found it"). As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment . </P> <P> The story first appeared in written form in Vitruvius' books of architecture, two centuries after it supposedly took place . Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time . </P>

Who came up with the idea of density