A typical ceilometer record during rainfall is examined and certain regular and recurring oscillations beginning uniformly at an angle of elevation of 48° and decreasing gradually with elevation are noted. These features are explained physically as “rainbow” effects. The angle of elevation of maximum oscillation is shown to be about 49° regardless of base-line length; the tapering off above is discussed. Possible “secondary rainbow” effects at lower elevation angles are mentioned. Finally, methods of differentiating between the rainbow effects and cloud layers are suggested.