In industry, a steam engine is a heat engine whose working substance is water. [1] The basic design of a functional steam engine, conceived to raise water out of mines, known as the Papin engine, was outlined in 1690 by French engineer Denis Papin in his "A New Method to Obtain Very Great Motive Powers at Small Cost." [2] On this design, the first two operational steam engines were built soon thereafter, the "Miner's Friend" (1698) and the "Atmospheric Engine" (1712), made respectively by English engineers and associates Thomas Savery and Thomas Newcomen. [3]

The physics underlying the operation of the steam engine, specifically the understanding of how fire (or heat) creates cyclical mechanical movement (up and down piston movement), through its actions on an intermediate substance (water), is the basic science of thermo-dynamics, initiated with the 1824 publication Reflections on the Motive Power of Fire by French physicist Sadi Carnot.

The “veritable creators” of the steam engine, starting with Savery and Newcomen, according to Carnot, are English engineer John Smeaton, who made an improved Newcomen engine (1775), Scottish engineer James Watt, who made a number of improvements to the Newcomen engine, such as the separate condenser (1765), sun and planet gear (1781), centrifugal governor (1788), and indicator diagram (1796), English engineer Arthur Woolf, who designed an improved boiler for producing high pressure steam (1803) and invented a compound steam engine (1805), and English engineer Richard Trevithick who built the first steam engine automobiles (1801).

In each of these various heat engines, Carnot presumed that the key to their operation was the "re-establishment of equilibrium in the caloric". The theory was later proven false by German physicist Rudolf Clausius who, beginning in 1850, corrected this suppostion with the mathematical argument of "increase in entropy" in the cycle. [4]

References
1. Carnot, Sadi. (1824). Reflections on the Motive Power of Fire - and on Machines Fitted to Develop that Power. Paris: Chez Bachelier, Libraire, Quai Des Augustins, No. 55.
2. Galloway, Robert L. (1881). The Steam Engine and its Inventors. London: MacMillan and Co.
3. Savery, Thomas. (1702). The Miner's Friend – or an Engine to Raise Water by Fire, [URL]. London.
4. Clausius, R. (1865). The Mechanical Theory of Heat – with its Applications to the Steam Engine and to Physical Properties of Bodies. (Google Books). London: John van Voorst, 1 Paternoster Row. MDCCCLXVII.