THE NATURE OF THE PROBLEM THIS book results from an attempt to explain on a basis of experimental physics some of the many strange phenomena produced by the natural movement of sand over the dry land of the Earth. The subject is but one aspect of a far wider problem which is still very imperfectly grasped-the transport of solid particles of any kind by fluids in general. Here the difficulty has been, and still is, that no one branch of science has attempted to deal with the problem as a whole, or to co-ordinate the vast amount of piecemeal work by students of different outlook in many...