Note 66 — IV.[34] CARNOT’S THEORY OF THE MOTIVE POWER OF HEAT.[35] WITH NUMERICAL RESULTS DEDUCED FROM REGNAULT’S EXPERIMENTS ON STEAM.[36]

From this point of view, we see very clearly how imperfect is the steam-engine, even after all Watt’s improvements. For to “push the principle of expansion to the utmost,” we must allow the steam, before leaving the cylinder, to expand until its pressure is the same as that of the vapor in the condenser. According to “Watt’s law,” its temperature would then be the same as (actually a little above, as Regnault has shown) that of the condenser, and hence the steam-engine worked in this most advantageous way has in reality the very fault that Watt found in Newcomen’s engine. This defect is partially remedied by Hornblower’s system of using a separate expansion cylinder, an arrangement the advantages of which did not escape Carnot’s notice, although they have not been recognized extensively among practical engineers, until within the last few years.