SNOW-WAVES AND SNOW-RIPPLES 183 



On the Distance to which Hedges and Belts of 

 Trees Extend Shelter from the Wind. 



The wind curves round the sides of a narrow 

 obstruction, and its direct horizontal movement is 

 therefore already felt not far to leeward. In the 

 case of a quickset hedge, or a wall, or a belt of 

 trees, the distance to which shelter extends depends 

 upon the height of the obstruction. In the snow- 

 waves the direct forward wind was kept away from 

 the ground for a distance twenty-five times as great 

 as the height of the ridge. Applying this to the 

 case of fields enclosed by thick quickset hedges, I 

 conclude that a hedge 5 feet high would give 

 effective shelter from' the wind to young growing 

 crops for a distance of at least 125 feet. Trees 

 planted in long, narrow belts, in the way more 

 common in Scotland than in England, must extend 

 effective wind-shelter for a considerable distance, 

 that for trees of 30 feet high being at least 750 

 feet or 250 yards. 



On the Three Modes of Deposition of Drifted 

 'Material Depending upon Rate of Subsidence. 



The circumstance that size, density, and shape 

 each have an influence on the mobility of solid 

 particles under the action of a current of air or 

 water has hampered observers and writers in their 



