  The variational method with constraints recently developed by Verkley and
Gerkema to describe maximum-entropy atmospheric profiles is generalized to
ideal gases but with temperature-dependent specific heats. In so doing, an
extended and non standard potential temperature is introduced that is well
suited for tackling the problem under consideration. This new formalism is
successfully applied to the atmosphere of Venus. Three well defined regions
emerge in this atmosphere up to a height of $100 km$ from the surface: the
lowest one up to about $35 km$ is adiabatic, a transition layer located at the
height of the cloud deck and finally a third region which is practically
isothermal.
