14 In Praise of Robert Stirling

Stirling's engine preceded that of Sadi Carnot by 8 years. It relied on the principle of reversible heat exchange, was patented, built and put into service. In a more genteel era (1884), Fleeming Jenkin put it this way:

‘You have, therefore, a theoretically perfect heat engine, every portion of the action of which is reversible, and reversibility, as you have no doubt been told in previous lectures, is the test of a perfect engine. Stirling's is a perfect engine and it is the first perfect engine ever described.’

(In fact, the inevitable element of thermal conduction is irreversible, but Jenkin's meaning is clear.)

Carnot's engine, by contrast, is an abstraction, was not patented, was not built and never will be. The Carnot cycle is celebrated and known to every student of engineering and physics. Where the Stirling cycle gets a mention it is misunderstood and misrepresented, even down to the fourth and latest edition of the UK's most widely used teaching text on engineering thermodynamics (Rogers and Mayhew 1992).