# Caloric theory

The Caloric theory of heat is an early theory of thermodynamics, developed mostly during the 18th and 19th centuries, which claims that changes in temperature are due to the transfer of was an invisible, weightless fluid called "caloric". The theory originally hinged on two key assumptions: 1) "heat was a 'self-repulsive' (or 'elastic,' or 'expansive') substance, while it was attracted to ordinary matter," and 2) "temperature was the density of caloric" (Chang, 2003). Later calorists were also generally committed to the claim that since heat was a material substance, it could neither be created nor destroyed; i.e., that heat was conserved (See, for example, Reflexions on the motive power of fire, by Sadi Carnot.)

Quite a number of successful explanations can be (and were) made from these hypotheses alone. We can understand why a cup of tea cools at room temperature: caloric is self-repelling, and thus slowly flows from regions dense in caloric (the hot water) to regions less dense in caloric (the cooler air in the room). We can explain the expansion of air under heat: caloric is absorbed into the molecules of air, which increases its volume. If we say a little more about what happens to caloric the during this absorption phenomenon, we can explain the radiation of heat, the state changes of matter under various temperatures, and deduce nearly all of the gas laws.

However, one of the greatest confirmations of the caloric theory was Laplace’s theoretical correction of Newton’s pulse equation. Laplace, a calorist, added a constant to Newton’s equation, which we refer to today as the specific heat capacity ratio of a gas. (See Laplace, 1816).This addition not only vastly corrected the theoretical prediction of the speed of sound, but also continued to make even more accurate predictions for almost a century afterward, even as measurements of the ratio of specific heats became more precise.

Due to the work of James Prescott Joule and others in the 19th century, a competing theory began to gain popularity, which characterized heat as a kind of motion. Then in 1850, Clausius published a paper showing that the two theories were compatible, as long as the calorists principle of the conservation of heat. In this way, the Caloric theory disintegrated into the annals of physics, to be replaced by modern thermodynamics, in which heat is the kinetic energy of molecules.

The Caloric Theory has recently reemerged as a point of consideration in the debate over Scientific Realism in the philosophy of science. Realists tend to suggest that the success of a theory is dependent on the truth of that theory. However, the Caloric Theory is considered by some (for example, see Lauden, 1981) to be a counterexample to this claim.ja:カロリック説

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