Comment by adastra22

The steam engine is more than just boiling water. It is a thermodynamic cycle that exploits differences in the pressure curve in the expansion and contraction part of the cycle and the cooling of expanding gas to turn a temperature difference (the steam) into physical force (work).

To really understand WHY a steam engine works, you need to understand the behavior of ideal gasses (1787 - 1834) and entropy (1865). The ideal gas law is enough to perform calculations needed to design a steam engine, but it was seen at the time to be just as inscrutable. It was an empirical observation not derivable from physical principles. At least not until entropy was understood in 1865.

James Watt invented his steam engine in 1765, exactly a hundred years before the theory of statistical mechanics that was required to explain why it worked, and prior to all of the gas laws except Boyle’s.