58 



WINDBREAKS. 



(diagram 25) are found at the same point relative to the windbreak 

 and exceed about equally (in this case by about 4J F.) the maximum 

 and minimum temperatures in the open. In other words, the daily 

 range of temperature is nearly 9 F. greater in the protected area 

 than where the air is allowed to circulate freely. 



(2) In the zone of windbreak influence the highest temperatures 

 on clear, sunny days, and the lowest temperatures on clear, cool 



a&vse afore , cor r0# 0000 sw *s# 



DIAGRAM 26. Heating efficiency of various windbreaks during hours of sunshine, as shown by 

 summation of temperatures above 5C. or 41F. (growing temperature). Thermometers read hourly 

 between 9 a. m. and 5 p. m., midsummer. 



nights, correspond in position to the point of greatest windbreak 

 efficiency, as indicated by the evaporation curves (diagrams 16 to 

 24), which is the point of greatest air stagnation. 



(3) Just as the efficiency of a good windbreak increases with the 

 increase of wind velocity in the open, so the degree of superheating 

 in the daytime and of cooling at night, due to stagnation, increases 

 likewise (diagrams 28 and 31). 



