  We discuss the simple microscopic derivation of a hydrophobic effect. Our
approach is based on the standard functional representation of the partition
function of interacting classical particles and subsequent passage to
collective variables (local densities of the solvent). We get an expression for
the solvation free energy of solute molecule of any arbitrary shape and derive
the nonlinear equation for the mean solvent density surrounding the solvated
object. We pay a special attention to some inconsistencies between the
microscopic consideration and the two-length scale mean-field theory of
hydrophobic effect.
