Lessening Destructive Effects of "Winds 169 



the wind. The writer has observed that when the 

 rate of evaporation at 20, 40, and 60 feet to the lee- 

 ward of a grove of black oak 15 to 20 feet high was 

 11.5 c.c., 11.6 c.c., and 11.9 c.c., respectively, from a 

 wet surface of 27 square inches, it was 14.5, 14.2 and 

 14.7 c.c., at 280, 300 and 320 feet distant, or 24 per 

 cent greater at the three outer stations than at the 

 nearer ones. So, too, a scanty hedge-row produced 

 observed differences in the rate of evaporation as fol- 

 lows, during an interval of one hour : 



At 20 feet from the hedge- row the evaporation was 10.3 c.c. 

 At 150 " " " " " " " 12.5 c.c. 



At 300 " , " " " " " " 13.4 c.c. 



Here the drying effect of the wind at 300 feet was 

 30 per cent greater than at 20 feet, and 7 per cent 

 greater than at 150 feet from the hedge. 



Then, too, when the air came across a clover field 

 780 feet wide the observed rates of evaporation were : 



At 20 feet from clover 9.3 c.c. 



At 150 " " " 12.1 c.c. 



At 300 " " " 13 c.c. 



Or 40 per cent greater at 300 feet away than at 20 feet, 

 and 7.4 per cent greater than at 150 feet. 



The protective influence of grass lands, and the dis- 

 advantage of very broad fields on these light lands, 

 was further shown by the increasingly poorer stand of 

 young clover as the eastern margin of these fields was 

 approached, even when the drifting had been inappre- 

 ciable. Below are given the number of clover plants 



