The principal question studied in Mestel (1953) was: under what conditions will the E-S circulation through the radiative envelope ensure that a Cowling-type main sequence star stays effectively homogeneous? The E-S velocities v are of order (L/Mg)(Ω2r/g), so that the circulation time tcirc is ⋍ t(ΩKelvin-Helmholtz)/(Ω2 r/g), where the bar indicates a mean value. The circulation advects nuclear-processed material from the convective core, and so sets up horizontal variations δµ in mean molecular weight µ. The condition of hydrostatic support requires corresponding horizontal temperature variations; the consequent local breakdown in radiative equilibrium yields a “µ-current” (analogous to the E-S “Ω-current”) with velocities vµ estimated roughly as (L/Mg) (δµ/µ). The total velocity vμ is the linear superposition v∽Ω + v∽µ, each constructed using first-order perturbation theory. The µ-distribution that fixes v∽µ is itself determined by the circulation: