CONTENTS 



PART I 



AEOLIAN SAND-WAVES 



CHAPTER I 



DESERT SAND-DUNES 



PAGE 

 31 



Sand-waves near Helwan, their height and length — 

 Formation of peaks on the ridges — Course of the wind 

 as it blows over a series of the ridges, direct current 

 and eddy — Note on the wind-screen of motor vehicles 

 and the return current — Height of wave limited by 

 velocity of wind — Significance of constant ratio of 

 length to height — The eddy-curve ichthyomorphic, with 

 blunt head and fine tail — Longitudinal bank to leeward 

 of a peak — On the formation of the pits called fuljes — 

 Travelling mounds of sand of crescentic shape, called 

 barchans — Rate of advance of the sand- waves — Mode 

 by which the undulations originate in a level deposit 

 of sand — On a limit to the size of level ridges due to 

 fineness of the sand — Large dunes east of the Suez 

 Canal — Illusion of mountainous size — Formation of 

 dew upon the sands — Dunes west of Suez Canal ; in- 

 fluence of moist ground on their formation — Effect of 

 electrification upon the mobility of sand — On the sizes 



of the sand-grains. 



15 



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