In the absence of turbulence or convection one expects that, in stars, heavy elements would tend to settle gravitationally while light elements would go to the surface. Eddington (1930) however realized that this general tendency could be modified both by the electric field and by differential radiation pressure. In spite of their small mass, electrons do not all float on the surface of stars because an electric field is generated that keeps them from separating from the protons. Instead of settling gravitationally, heavy elements often concentrate on the surface because they absorb relatively much more photons than hydrogen or helium and are dragged to the surface by the radiative flux. Eddington concluded that turbulence was too strong for diffusion to be important in stars since the relation that diffusion predicts between surface abundances and stellar masses did not appear to be realized in most stars.
Finite element simulation of the effect of surface roughness of coaxial electrodes on small mass and force measurements using a voltage balance apparatus