Gravity effects on the correlation length in gases near the critical point

The paper deals with the question how critical fluctuations in gases are affected by the presence of a gravitational field. We have investigated the effects of gravity using a squared-gradient approximation for the free energy density. It is found that the order-parameter correlation function and, hence, the scattering function becomes anisotropic and that the correlation length remains finite in all directions. Data are presented yielding the correlation length parallel and perpendicular to the gravitational field as a function of the temperature and of the vertical position in the gas.