"On the Motive Power of Heat"
In February 1850, Rudolf Clausius addresses anomalies in the energy economy in “On the Motive Power of Heat.” Image: Photograph of Rudolf Clausius. This image is in the public domain in the United States because its copyright has expired.
In subsequent work Clausius develops, describes mathematically, and eventually gives a name (1865) to the concept of Entropy; and then (1867) spells out the terminal condition of the universe under its iron law.