Photographs and simultaneous temperature measurements show that the thermal oscillations which occur in air between horizontal plates with unstable stratification are associated with lateral oscillations of wavy convection rolls. The phenomenon appears to consist of an oscillating motion nearly independent of depth superimposed upon the convective motions, and is best viewed from above. For large Prandtl number the photographic evidence suggests that the first unsteady motions to occur consist of a very similar oscillation, except that the features which oscillate are updraft and downdraft lines of short length. The periods of the oscillations obtained visually agree well with those reported previously from fixed temperature measurements, and a weak oscillation of doubled frequency is explained.