<P> For the foundations of thermodynamics, the conceptual importance of this was emphasized by Bryan, by Carathéodory, and by Born . The reason is that calorimetry presupposes a type of temperature as already defined before the statement of the first law of thermodynamics, such as one based on empirical scales . Such a presupposition involves making the distinction between empirical temperature and absolute temperature . Rather, the definition of absolute thermodynamic temperature is best left till the second law is available as a conceptual basis . </P> <P> In the eighteenth century, the law of conservation of energy was yet to be fully formulated or established, and the nature of heat was debated . One approach to these problems was to regard heat, measured by calorimetry, as a primary substance that is conserved in quantity . By the middle of the nineteenth century, it was recognized as a form of energy, and the law of conservation of energy was thereby also recognized . The view that eventually established itself, and is currently regarded as right, is that the law of conservation of energy is a primary axiom, and that heat is to be analyzed as consequential . In this light, heat cannot be a component of the total energy of a single body because it is not a state variable, but, rather, is a variable that describes a process of transfer between two bodies . The adiabatic process is important because it is a logical ingredient of this current view . </P> <P> This present article is written from the viewpoint of macroscopic thermodynamics, and the word adiabatic is used in this article in the traditional way of thermodynamics, introduced by Rankine . It is pointed out in the present article that, for example, if a compression of a gas is rapid, then there is little time for heat transfer to occur, even when the gas is not adiabatically isolated by a definite wall . In this sense, a rapid compression of a gas is sometimes approximately or loosely said to be adiabatic, though often far from isentropic, even when the gas is not adiabatically isolated by a definite wall . </P> <P> Quantum mechanics and quantum statistical mechanics, however, use the word adiabatic in a very different sense, one that can at times seem almost opposite to the classical thermodynamic sense . In quantum theory, the word adiabatic can mean something perhaps near isentropic, or perhaps near quasi-static, but the usage of the word is very different between the two disciplines . </P>

When does an adiabatic process happen in the atmosphere