Rudolf Clausius

Clausius publishes his first mechanical-theory-of-heat paper

Clausius rescued Carnot's celebrated engine result by discarding the very heat-fluid theory Carnot had used to derive it.

1850: a landmark paper in two halves

In 1850, Rudolf Clausius published "Ueber die bewegende Kraft der Wärme und die Gesetze, welche sich daraus für die Wärmelehre selbst ableiten lassen" in Annalen der Physik und Chemie.

It ran in two installments: pages 368 to 397, then resuming more than a hundred journal pages later at 500 and running to 524.

The contradiction he was there to fix

Sadi Carnot's theorem about ideal heat-engine efficiency worked, but Carnot had derived it while treating heat as a conserved, indestructible fluid. James Prescott Joule's experiments had since shown a quantitative equivalence between heat and mechanical work.

Clausius kept the engine result and threw out the caloric assumption used to justify it, incorporating energy conservation into a modern theory of heat.

A sentence that sounds ordinary

The paper introduced the principle that heat cannot of itself pass from a colder body to a hotter one — a foundational formulation of what became the second law of thermodynamics.

The word "entropy" appears nowhere in it. Clausius developed the transformation theory further in 1854 and coined that term only in 1865.

The English paper usually cited as "On the Moving Force of Heat" came out in Philosophical Magazine in 1851, and is sometimes mistaken for the 1850 original.

Sources

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What the sources leave uncertain

The publication year and journal pagination are secure, but the sources consulted do not establish a precise day when each journal installment was issued.
Bibliographies cite the same journal run as volume 79 in contemporary Poggendorff numbering and volume 155 in Wiley’s cumulative Annalen numbering; these are not different papers.
The English translation titled “On the Moving Force of Heat” appeared in Philosophical Magazine in 1851, so that English publication should not be confused with the original German event of 1850.