56 



WINDBREAKS. 



have been made, have been explained. The season of 1908 was 

 peculiar in the Middle West, in that the rainfall was excessive and 

 the mean temperatures, because of the unusual amount of cloudy 

 weather, were below normal. Consequently, while it was expected 

 that the benefit arising from windbreaks would be found to be the 

 result of their effect upon evaporation, a careful analysis of the figures 

 indicates that in that season the evaporation was not excessive and 

 that the real benefit from windbreaks came through their ability to 

 affect temperatures. Table 10 gives the climatic data from two 

 Weather Bureau stations in Kansas and Nebraska, and compares 

 1908 with the average of about 20 earlier years. These figures signify 

 that windbreak effects upon crops in a normal year might be some- 

 what different from those recorded fn 1908, though the measurements 

 of evaporation indicate that an equal amount of benefit may be 

 expected in the driest years. 



TABLE 10. Wind velocity, precipitation, temperature, and humidity for 1908, as com- 

 pared with the normal. 



MEASUREMENTS OF AIR TEMPERATURES. 



Diagram 25 shows graphically the highest and lowest temperatures 

 measured on both sides of a dense grove and within it when there was 

 a constant wind velocity of from 7 to 8 miles per hour. As in all 

 similar cases, the observed temperature in the open is taken as a nor- 



