Cross spectra between long time series (5–10 years) of pressure data from 27 stations and that from Canton Island show peaks in the coherence squares near 5-day periods. Phase angles indicate that these peaks are manifestations of a westward propagating, zonal wavenumber 1 disturbance. Sea-level pressures and 500-mb heights recorded during the IGY are filtered in time and harmonically analyzed in space revealing the westward propagating 5-day waves. A composite wave based on the IGY sea-level pressure data suggests that the amplitude of the disturbance increases with increasing latitude. The observed characteristics of the 5-day pressure wave are shown to he not inconsistent with those of a planetary wave, or wave mode of the second class, theoretically predicted by Laplace's tidal equations.