Nevertheless, the predictions of classical tidal theory still did not agree with observations. It was Lindzen, in his 1966 paper, "On the theory of the diurnal tide", who showed that the solution set of Hough functions given by Bernhard Haurwitz to Laplace's tidal equation was incomplete: modes with negative equivalent depths had been omitted. Lindzen went on to calculate the thermal response of the diurnal tide to ozone and water vapor absorption in detail and showed that when his theoretical developments were included, the surface pressure oscillation was predicted with approximately the magnitude and phase observed, as were most of the features of the diurnal wind oscillations in the mesosphere. In 1967, along with his NCAR colleague, Douglas D. McKenzie, Lindzen extended the theory to include a term for Newtonian cooling due to emission of infrared radiation by carbon dioxide in the stratosphere along with ozone photochemical processes, and then in 1968 he showed that the theory also predicted that the semi-diurnal oscillation would be insensitive to variations in the temperature profile, which is why it is observed so much more strongly and regularly at the surface.