NOTES. 



439 



in the leafy season, though the difference is not great. De- 

 ciduous and evergreen trees show but slight differences in 

 this respect. More rain is usually caught by gauges at a 

 given height above the forest crown than at the same height 

 in open fields, but it still remains doubtful whether the rain- 

 fall itself is really larger over the forests, since the recorded 

 catch of the rain gauge still requires a correction for the in- 

 fluence of the force of the wind at the gauge. 



In such cases, where over a large area deforestation and 

 reforestation have seemingly gone hand in hand with de- 

 crease and increase of rainfall, the possible secular change in 

 rainfall must also be considered. Yet the experience of in- 

 creased rainfall over the station at Lintzel, with increase of 

 forest area, points strongly toward a possible interdependence 

 under given conditions. 



By condensing dew, hoar frost, and ice on their branches, 

 trees add thereby a little to the precipitation which reaches 

 the ground, and by preventing the rapid melting of snow 

 more water remains available under forest cover. 



The question as to the march of destructive hailstorms with 

 reference to forest areas, which seems settled for some regions 

 in France, remains in doubt for other, especially mountain, 

 regions. 



From these statements we would expect as a consequence 

 of deforestation an effect on the climate of the deforested area 

 in three directions, namely : (a) extremes of temperature of air 

 as well as soil are aggravated, () the average humidity of the 

 air is lessened, and possibly (c) the distribution of precipi- 

 tation throughout the year, if not its quantity, is changed. 



INFLUENCE OF FORESTS UPON THE CLIMATE OF THE 

 SURROUNDING COUNTRY. 



(i) An influence of the forest upon the climate of its sur- 

 roundings can only take place by means of diffusion of the 

 vapor which is transpired and evaporated by the crowns, and 



