60 



WINDBREAKS. 



registers no difference in the temperatures within and without the 

 zone of windbreak influence. (See discussion of " Sensible tempera- 

 tures.'') 



(6) The warmth collected in and under the trees will be appreciable 

 at night for a short distance on both sides of the windbreak, unless 

 rapidly diffused by a high wind. The amount of warmth so collected, 



68.3' 



DIAGRAM 28. Influence of dense grove (cottonwood and ash) on nocturnal cooling of iiir. With wind 

 velocities of 6, 3, and 1 miles per hour. 



and the extent of its measurable influence, will increase with the 

 width and area of the windbreak. 



(7) During precipitation, the effect of the windbreak is beneficial 

 because it checks the velocity of the wind which gives a penetrative 

 force to the particles of moisture, and which also causes excessive 

 cooling by evaporation from the moistened surfaces. This checking 



