The rotation angle and fractional linear polarisation as a function of the magnetic field in the presence of preferential acceleration. The higher the solar outflow, the more the plane of linear polarisation rotates. The upper curves (full lines) are reference cases for the normal solar outflows given by the model of Wang et al. (1993), the ones below (dotted curves) have their outflow velocity multiplied by two, the broken lines have their outflow velocities multiplied by three, the dot-line-dot curves have their outflow multiplied by four, and the lowest curves (three dots and one line) have the nominal value of the solar outflow multiplied by a factor of five.