RESULTS OF MEASUREMENTS. 



57 



mal, and other temperature lines are shown at intervals of 1 F. above 

 and below this normal. Diagrams 26 and 27 express the summation 

 of temperatures, or the total amount of heat registered at various 

 points relative to the windbreak during the hours of insolation. The 

 summation at each point is expressed as a percentage of the sum of 

 the hourly temperatures in the open, which is taken to be 100 per 

 cent of heat for the day in question. The summations include tem- 

 peratures from 5 C. or 41 F. upward. 1 The first diagram repre- 

 sents conditions in warm September days; the second, conditions 

 when the temperatures were scarcely above the growing temperature. 

 Diagrams 28 to 31 show the lowest temperatures recorded on a 

 number of nights, in relation to four classes of windbreaks and under 



DIAGRAM 25. Effect of dense groves on daily range of air temperatures, with wind velocities of 7 to 8 

 miles per hour. Normal maximum temperature 92.3 P.; normal minimum temperature 66.3 F. 



various atmospheric conditions. In each case the figure on the curve 

 refers to the probable lowest wind velocity as estimated from the 

 average velocity for the entire night. Some of the results (as Oj 

 diagram 30) were obtained in cornfields simultaneously with the 

 results obtained in an open field bearing a similar relation to the 

 windbreak. 



From a careful study of the results shown in these diagrams the 

 following deductions may be drawn: 



(1) Other conditions being equal, both the highest maximum tem- 

 perature at midday and the lowest minimum temperature at night 



1 According to De Candolle, vegetative growth does not begin until the temperature reaches a height of 

 about C C. or 42 F., and a similar basis has been used in all calculations to show the total effect of the 

 windbreak on the possibilities of crop growth. 



