Comment on: "Sadi Carnot on Carnot's theorem"

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Carnot established in 1824 that the efficiency ηC of reversible engines operating between a hot bath at absolute temperature Thot and a cold bath at temperature Tcold is equal to 1-Tcold/Thot. Carnot particularly considered air as a working fluid and small bath-temperature differences. Plugging into Carnot's expression modern experimental values, exact agreement with modern Thermodynamics is found. However, in a recently published paper ["Sadi Carnot on Carnot's theorem", Am. J. Phys. 70(1), 42-47, 2002], Guemez and others consider a "modified cycle" involving two isobars that they mistakenly attribute to Carnot. They calculate an efficiency considerably lower than ηC and suggest that Carnot made compensating errors. Our contention is that the Carnot theory is, to the contrary, perfectly accurate.