PROGKESS OF METEOKOLOGY IN 1889. 2G9 



over the forest or was restored to the soil iu tlie form of raiu, it would 

 be of great utility, but the wind carries this vapor away and disperses 

 it on all sides, so that its useful eflect to our owu country is scarcely, if 

 at all, perceptible. Accordingly, the diflerence of absolute as well as 

 ol relative humidity between the cultivated i^atches in our extensive 

 forest districts and the cultivated plains of our country is very slight or 

 almost nil. It is true that relative humidity is greater under trees, 

 and as the relation mentioned does not apply to open spaces surrounded 

 by wood, this difference in humidity can have no practical importance. 



The lakes and large swamps as well as marshes have a much greater 

 influence on atmospheric humidity than the forests. The evapora- 

 tion from the latter, for equal areas, is fiir less than from the former. 

 Tlie draining of lakes and swamps has not been regarded with serious 

 alarm. 



One effect of forests on atmospheric humidity which seems to be useful 

 to vegetation and agriculture is the increase of dew in clearances; but 

 this increase of dew is not attributable to a greater abundance of vapor 

 in the forests, but to the increase of terrestrial radiation induced by the 

 forest. 



The agriculturists of Smaland and of JemtlaudTiave preferred bare, 

 dry, elevated lands, exposed to wind, to fields at a lower level, wooded 

 and moist, but more subject to frost. 



If all the forests were cleared what would be the result for the atmos- 

 pheric humidity in Sweden 1 Supposing that this clearance did not 

 materially modify the quantity of rain that falls, and it is not proved 

 that it would, it seems to us that the amount of vapor contained in the 

 stratum of air in which we live would not be altered in a way which 

 would materially influence vegetation. Probably relative humidity 

 would be slightly reduced in summer, because temperature would rise 

 slightly. 



In Bulletin No. 2 of the Forestry Division of the Department of Ag- 

 riculture, Mr. G. H. Parsons discusses the relation of the climate of 

 Colorado to the growth of trees. The author finds that the great range 

 of temperature, the warmth of the sun's rays in cokl weather, the low 

 humidity, small rain-fall, rapid evaporation, small cloudiness, and the 

 northers and chinooks are unftivorable to tree growth. Even irri- 

 gation can only partially supply the tree with the moisture it needs, 

 and can never give it the luxuriant foliage characteristic of moist cli- 

 mates. 



EffevU of forest destruction. — Mr. W. E. Abbott has observed that 

 deforestation in New South Wales has been followed by a more abun- 

 dant flow of water in the streams ; springs have broken out, dry water- 

 courses have begun to flow, and the change is apparently permanent. — 

 [Journ. Boy. 8oc. New South Wales, xxii, p. 59.) 



Dr. O. Birkner finds that in Saxony the forests interpose an obstacle 

 to the rapid run-ofiof the rain fall in heavy rains and thereby prevent 



