The absorption of MF radio waves is related to electron densities and collision frequencies in the D and E regions of the ionosphere. Currently accepted collision frequencies require the full phase integral method to be used when calculating absorption. A simple correlation is derived for correcting the ray theory result. Geometrical optics for multiple reflections between cylindrical and plane reflectors show that focusing occurs for analytic values of the curvature. The amplitude probability distribution should be measured when the absorption is being determined. Absorption at Birdlings Flat is found to have no significant relationship to any other geophysical parameter. A longer time series of Campbell Island fmin shows no meteorological influences; only geomagnetic effects can be detected. The variance of temperature increases with altitude (100 to 30 mb) in the winter stratosphere over Christchurch and Campbell Island at periods above 7 days.