  We show that various types of equilibrium play an important part in the
behaviour of the troposphere. In analogy to the electro-chemical potential
(well-known in solid-state physics and electro-chemistry) a gravito-chemical
potential and a gravito-thermo-chemical potential, as well as the corresponding
equilibria are introduced. We shall show that (a) the isothermal atmosphere is
characterized by a constant gravito-chemical potential; (b) the well-mixed or
adiabatic atmosphere is characterized by a constant gravito-thermo-chemical
potential. Thus, a linear decrease of the temperature with the vertical
coordinate corresponds to a state of equilibrium.
