6G 



FOREST INFLUENCES. 



Fig. 30 is that for the .station with the greatest elevation above 

 the surface (Hagenau), and Fig. 31 that for the least (Schoo). They 

 show great differences, but there is no connection between the dia- 

 grams through those for the intermediate stations. They are alike, 

 and of especial interest, in that in both the reduction of the minima is 

 only a small fraction of a degree. Fig. 32 (Neumath) gives the only 

 case where the maxima were warmed decidedly more than the minima. 

 This increases the range and makes the temperature more excessive in 

 the late winter and early spring months. 



Pig. 33. — Average dififerences of tree-top temperature, sixteen German Stations (TF — O). 



The average differences of tree-top temi>eratures ( ^\'-0') are graphic- 

 ally given in Fig. 33. It is at once seen to be very similar to the corre- 

 sponding Figure (17) for the elevation of 5 feet. Tlune is the same 

 elevation of minima, the same lowering of maxima, the same cooling 

 effect, and the same exaggeration of all features in summer. The le- 

 duction of mininui is, however, more nearly equal to that of the maxima, 



Fig. 34.— Tree-top temperature differences for four stations with average height of 21 feet. 



and there is, consequently, less cooling. It seems, therefore, that the 

 tree-top station is intermediate in temperatures between the base 

 station and that in open fields. 



It will be interesting to see if there is any difference through the 

 year on account of elevation of the tree tops above the ground. To 

 ascertain this the four lowest stations were taken (two in evergreens 

 and two in deciduous trees) and tlieir values of W'-O' were c<mibiued. 

 The result is Fig. 3i. The average height was lil feet. The four 



