Data obtained from the selective chopper radiometer on the Nimbus 5 satellite provide a four dimensional (space and time) view of the temperature structure of the middle atmosphere. Spectral analyses of these observations enable the structure of the large scale planetary waves (zonal wavenumbers 1-6) to be deduced. Analyses of two years of data (1973-4) reveal the important differences that exist between the wave motions in the two Hemispheres. In the Northern Hemisphere the wave motions are dominated by stationary waves, whereas in the Southern Hemisphere, eastward travelling waves are more in evidence. A detailed investigation of data during December-February 1973-4 reveals westward travelling wave 1 components with periods of 5.8, 8.3 and 12.3 days.