The origin and growth of ripple-mark.

The object of the investigation was to determine how ripple-mark started in perfectly smooth sand, apart from accidental variations of surface friction; how the ripples grew; how the amplitude and depth of the water affected them; and whether there was any connection between ripple-mark and kindred phenomena, such as the dust figures in a Kundt’s tube. In the course of the investigation the causes, form, and mode of action of “ripple vortices” in the water were determined, and the fact that no vortices of this kind can form in a current flowing steadily in one direction over an obstacle was demonstrated, both theoretically and practically. Also many minor details came to light, such as the fact that each ripple is continually travelling, as a whole, and why it does so.