154 WAVES OF SAND AND SNOW 



and a fine end, which was a containing, or 

 boundary, curve for all these structures, but that 

 for the stationary structures the curve had its blunt 

 end to windward and for the travelling drifts or 

 waves to leeward, at least as far as their vertical 

 profile was concerned (Fig. 15). 



The stationary drifts, when complete, filled the 

 whole curve. The travelling drifts or waves 

 occupied only part of it. I was at first satisfied 

 by the mere fact that I had recognized utiity of form 

 among the fantastic shapes assumed by snowdrifts 



Fig. 15 



The Pundamental curve ofsnow dri-Fts. 



at various stages of their growth in the neighbour- 

 hood of obstructions of diverse kinds, but I 

 presently realized that the general curve which I 

 had drawn so as to satisfy my eye had a wide 

 significance, that it was one familiar in other 

 aspects of nature than snowdrifts — that it was, in 

 fact, the containing curve of eddies. The recog- 

 nition of this fact made it much easier to under- 

 stand the mode of formation and the movements 

 of the structures I had been examining in both 

 sand and snow, particularly when extending their 

 study to three dimensions and not dealing merely 



