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Ripple marks on sand dunes were observed by means of time-lapse motion picture photography as they moved with wind in their natural environment. When the film is projected the ripples appear to move rapidly. A wind-velocity meter was arranged to show in some of the pictures enabling instantaneous values to be read and correlated with ripple movement. Various modes of movement are shown including ripples reforming on areas which had been smoothed, ripples changing direction as wind direction changed, and wave lengths changing after the addition to an area of coarser sand.
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