Here, as common experience demonstrates, when a hot body "T1", such as a furnace, is put into physical contact, such as being connected via a body of fluid (working body), with a cold body "T2", such as a stream of cold water, energy will invariably flow from hot to cold in the form of heat "Q", and given time the system will reach equilibrium. Entropy, defined as Q/T, was conceived by Rudolf Clausius as a function to measure the molecular irreversibility of this process, i.e. the dissipative work the atoms and molecules do on each other during the transformation.