Note 70 — IV.[34] CARNOT’S THEORY OF THE MOTIVE POWER OF HEAT.[35] WITH NUMERICAL RESULTS DEDUCED FROM REGNAULT’S EXPERIMENTS ON STEAM.[36]

It being assumed that the temperatures of the boiler and condenser are the same as those of the Cornish engines. If, however, the pressure be lower, two atmospheres, for instance, the numbers would stand thus: The temperature in the boiler would be only 121. Consequently, for each pound of steam evaporated, only 614 units of heat would be required; and therefore the work performed for each unit of heat transmitted would be 160.3 foot-pounds, which is more than according to the estimate in the text. On the other hand, the range of temperatures, or the fall utilized, is only from 131 to 30, instead of from 140 to 30°, and consequently (Table II.), the theoretical duty for each unit of heat is only 371 foot-pounds. Hence, if the engine, to work according to the specification, requires a pressure of only 15 lbs. on the square inch (i.e., a total steam-pressure of two atmospheres), its performance is 160.3 371 or 43.2 per cent of its theoretical duty.