The Predecessors of Carnot
To the ancients, fire was the lightest of the four known elements. The concept of fire as an element lasted down to the time of Lavoisier, which was finally abandoned in favor of caloric theory. Phenomena involving the transfer of heat were imagined as being the result of a fluid, called “caloric,” which permeated the gaps between atoms of a solid causing thermal expansion and whose loss through the surface could explain Newtonian cooling. The work of Count Rumford on the heat produced by the boring of cannons was interpreted as coming from a solid; when work is done on it, it behaves like squeezing a sponge full of water.
At the close of the eighteenth century, technological advances in the creation of steam engines came predominantly from England. There was no consensus of what constituted heat, and the physics of the steam engine was virtually unknown. The dominating theory of the time was the caloric theory. Whereas in England caloric theory met its opposition by the semimechanical theories of Davy, Young, and Herapath, exerting their authority by invoking Newton, in France there was an almost complete acceptance of caloric theory, based on the authoritative personalities of the likes of Lavoisier, Poisson, and Fourier.
According to Lavoisier, caloric is to be treated as an indestructible substance that is conserved in all thermal processes, while, at the same time, heat and work are taken to be equivalent. Carnot’s analogy with a drop in the level of water (chute d’eau) through a mill with the descent of heat (chute de calorique), in a reversible engine, embodies this notion of indestructibility and the necessity for its conservation. Yet, heat is known to be produced by friction, so it appears or disappears when one rubs, or stops rubbing, his hands.
KeywordsHeat Capacity Adiabatic Compression Adiabatic Process Adiabatic Expansion Steam Engine
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