RESULTS OF MEASUREMENTS. 



47 



(4) If a windbreak is dense enough to resist the strongest wind, the 

 protection which it gives to any point in its lee increases with an 

 increase in wind velocity. In the case of a moderately dense wind- 

 break, the efficiency remains about the same under all conditions, 

 because the leakage through the windbreak is about the same pro- 



95 



X 



ZQ\ 



7 



/A/ 



OF #E/6ftr 



DIAGRAM 17. Protective efficiency of white pine belt. For wind velocities of 5, 10, and 15 miles per 

 hour, Height, 20 feet; width, 25 feet; 50 readings. 



portion of the total amount of wind. With a very open windbreak, 

 the efficiency decreases with an increase in wind velocity. 



The final test of a windbreak is the point in wind velocity at which 

 it reaches its greatest efficiency. Of the windbreaks examined, the 



