His most important paper, "On the Moving Force of Heat",[4] published in 1850, first stated the basic ideas of the second law of thermodynamics.

[5] Clausius was born in Köslin (now Koszalin, Poland) in the Province of Pomerania in Prussia.

Clausius's most famous statement of the second law of thermodynamics was published in German in 1854,[10] and in English in 1856.

[11] Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.During 1857, Clausius contributed to the field of kinetic theory after refining August Krönig's very simple gas-kinetic model to include translational, rotational and vibrational molecular motions.

This relation, which is a way of characterizing the phase transition between two states of matter such as solid and liquid, had originally been developed in 1834 by Émile Clapeyron.

[4][15][16]I prefer going to the ancient languages for the names of important scientific quantities, so that they may mean the same thing in all living tongues.

[17] The landmark 1865 paper in which he introduced the concept of entropy ends with the following summary of the first and second laws of thermodynamics:[4] The energy of the universe is constant.

The entropy of the universe tends to a maximum.Leon Cooper[16] added that in this way he succeeded in coining a word that meant the same thing to everybody: nothing.