54 FOREST INFLUENCES. 



rode, but is a type of all the curves, differing- cliiefly iu the magnitude 

 of the changes it indicates. The line of zero differences is used as the 

 base line of the diagram. On it are laid off", at equal distances, sea- 

 sonal lines, on which the values of W—0 for the monthly miniiua are 

 measured off, above the zero line if plus, below if minus. The points 

 thus obtained are connected by the dotted line above and this, there- 

 fore, is the curve representing the reduction (W—O) of the mininni. 

 In exactly the same way are constructed the curves for the mean 

 monthly values for W—O for maxima, represented by the broken line, 

 which is, therefore, the curve for the reduction of the maxima for the 

 year. Between these two curves is drawn a curve with unbroken line, 

 which represents tlie reduction {W—O) for the mean temperatures. 

 This figure shows at a glance all the details concerning the influence of 

 the forest on its own interior air temperatures. The distance vertically 

 between the exterior curves is the reduction of the range. The space 

 between the middle curve and the zero line represents the change in , 

 nu^nn temperature due to the influence of Avoods, cooling if the curve 

 lies below, warming if it lies above, the zero line. Where it lies below, 

 the space has been shaded to show phiinly tlie amount of cooling. In 

 this diagram, therefore, is shown the progress of all these elements 

 during the year. Analyzing the progress for Friedrichsrode (Fig. 10) 

 we see that the minima in the woods do not differ much from those out- 

 side between November and April. Then the forest begins to affect 

 them and the curve for W—O for minima rapidly rises above the zero 

 line. It reaches the greatest distance in August, ap]n'oaching the line 

 again from September to November, when the minima are once more 

 closely alike in the forest and outside. The forest has the greatest 

 effect on the minima in summer, somewhat less in May and September, 

 still less in April and Oc^tober. For the values of W—O for maxima 

 the progress is much tlie same, only in the reverse direction and two 

 or three times as great in magnitude. The greatest effect here falls in 

 July instead of August. It gives form to the W-0 values for mean 

 temperature, for which the greatest value falls in July. It appears also 

 that the temperature in the woods is almost always lower than in the 

 open fields. In March it is about the same; in winter it is a little cooler; 

 in summer it is de(;idedly cooler, especially in July. 



These figures for IF— are variously modilied in the various sta- 

 tions. Fig-. 11 (Uag-enau) shows a case where the reduction of the 

 minima, especially in summer, is relatively small, and the mean tem- 

 perature of the woods is less for the entire year. Fig. 12 (Sonnenberg) 

 represents a case where the red action of minima is almost as large as 

 that of the maxima and there is little reduction in mean tempera- 

 tures. In fact, the woods here are warmer in winter. In Fig. 13 

 (Eberswalde) the reduction of mean temperature is small and continues 

 during the year, like the preceding, but lor a different reason the 

 reduction of maxima and minima here run symmetrically, but shows no 

 great difference iu quantity. 



