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"A form of air-engine which was invented in 1816 by the Rev. R. Stirling is of special interest as embodying the earliest application of what is known as the "regenerative" principle, the principle namely that heat may be deposited by a substance at one stage of its action and taken up again at another stage but with little loss, and with a great resulting change in the substance's temperature at each of the two stages in the operation." —Encyclopedia Britannica, 1910

Stirling's Air Engine

"A form of air-engine which was invented in 1816 by the Rev. R. Stirling is of special interest as embodying…