Rudolph Gottlieb, after named Clausius, continued the study initiaded by Carnot, pursued by Joule and Lord Kelvin.
Clausius understood that the divergences between Carnot and Joule could be overcome. He got rid of the cocncept of "caloric" and he assumed that the heat could be explained by the conduct of the elementary particles of matter.
Clausius also gave us the extremely important principle: It is impossible for a self acting machine, unaided, to transfer heat from one body at a low temperature to another having a higher temperature.

Fathers of
thermodynamics:

S. Carnot

 J. P. Joule

Lord Kelvin

L. Boltzman