Quotes from Rudolf Clausius

The algebraic sum of all the transformations occurring in a cyclical process can only be positive, or, as an extreme case, equal to nothing. Statement of the second law of thermodynamics, 1862

Heat cannot of itself pass from a colder to a hotter body.

Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.

The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.