It is proposed that both the semi-diurnal and the diurnal components of the daily pressure wave are the result of horizontal divergence associated with the daily temperature variation. A combined theoretical-empirical approach suggests that the divergence can be attributed to the Brunt-Douglas isallobaric wind if certain modifications are introduced into the original Brunt-Douglas equation. These modifications include the retention of the vertical Coriolis term in the equations of motion, and the assumption that accelerations caused by changes in the thermal gradient are continually and automatically balanced by changes in the pressure gradient resulting from the horizontal divergence. The proposed theory offers a quantitative explanation for the observed latitudinal distribution of the daily barometric wave.