88 WAVES OF SAND AND SNOW 



different size so as to produce this result, and the 

 outcome of the inquiry is one of considerable im- 

 portance in its application to many phenomena of 

 the transport and accumulation of fragmentary 

 materials both by wind and water. 



Having hired a room and the necessary 

 appliances at a factory where designs are cut 

 in stone and glass by means of a blast of 

 hot sand, I proceeded to experiment with a 

 strong, steady blast issuing from a nozzle upon 

 materials obtained from natural sands by a process 

 of grading. I spread out a bed of coarse sand- 

 grains of nearly the largest size ordinarily found 

 upon sand-dunes — the " lag gravel," in fact — and 

 I turned upon it a strong blast of air under which 

 this small gravel moved with such freedom that 

 the grains rattled as they rolled. Nevertheless, 

 even under prolonged action of the blast there was 

 no sign of rippling. I then stopped the blast, and 

 taking some fine sand which was at hand, I mixed 

 a quantity of it with the lag gravel. I then turned 

 on the blast again, and almost instantaneously 

 ripples appeared and quickly became regular. 

 Their fronts were convex, being everywhere at 

 right angles to the direction of the blast issuing 

 from the nozzle. The large grains quickly collected 

 on the ridges in transverse barriers, whilst the rapid 



