PREFACE 13 



obliterate the transverse, and create longitudinal, 

 inequalities . 



Yet the smooth surface of the dry sand of the 

 desert and of the dry snow of the prairie is ruffled 

 transversely by the wind, and the transverse in- 

 equalities grow in size and become more nearly 

 regular in length and height, travelling, moreover, 

 in orderly procession before the wind, as passive 

 waves. Currents of water produce similar pro- 

 gressive waves on the surface of sandbanks. The 

 means by which these waves of sand and snow 

 originate, grow, and move are peculiar and interest- 

 ing. What I have been able to add to previous 

 knowledge of waves in sand and snow and the 

 eddies which make them is told in the following 

 chapters, where I have also recorded certain inci- 

 dental investigations on rippled clouds, on " snow- 

 mushrooms," on the undulations produced by 

 sledges, on quicksands, miniature deltas, and other 

 matters . 



I have to thank Dr. J. Scott Keltic, Secretary 

 of the Royal Geographical Society, for permission 

 to reproduce some of the plates and figures from 

 my papers in the Geographical Journal. 



V. c. 



WOODVILLE, CAMBERLEY. 

 September, 19 13. 



