200 DIMINUTION OF THE WATER OF RIVERS AND STREAMS. 



A similar result was arrived at by the investigation of the Smithsonian 

 Institution of the rain-measurements in Xorth America, where, on account 

 Oi the great extent of forest cleared away, a change in the proportion of 

 the de[)osits might well be expected. 



In regard to the old rain-observations, it should be remarked that they 

 were not taken daily, but at longer intervals of time, whereby their ac- 

 curacy was considerably impaired. Besides, the rain-gauges were fre- 

 quently not well placed, (upon roofs, towers, &c.) Both these circum- 

 stances, taken together, might produce an appearance of decrease in the 

 quantity of rain.* 



But although nearly two hundred years of direct rain- measurement 

 furniish no proof of a progressive decrease in the quantity of rain, in 

 "view of the facts presented by our author, (taken mostly from Milne 

 Home's essay in the Journal of the Meteorological Society of Scotland, 

 vol. 3, p. 35,) by Becquerel, Meteorological Atlas of the Observatory of 

 Palis for 18G7, Journal of Meteorology, vol. 4, p. 86, and by others, and 

 which appear to indicate a deterioration in the climate after the level- 

 ing of the forests, it would not be just to consider this hypothesis of no 

 importance. 



The commission consequently concluded that an influence of the woods 

 upon the amount of rain deposited, and especially upon the yearly con- 

 tribution, is probable, although direct observation does not give sufid- 

 cient evidence to determine its extent, or positively its existence. 



The copiousness of the springs and the fullness of the rivers, more- 

 over, do not entirely represent the amount of the yearly precipitation 

 of water. On the one hand a portion is given back to the atmosphere 

 by evajioration, and on the other a portion, determined in amount by 

 the physical conditions of the ground, penetrates into the soil, and af- 

 fords nourishment for the springs. The influence of the woods in both 

 these teudeucies cannot be overestimated. 



Through direct observation in France and the forest meteorological 

 station of Bavaria, it is evident that the oscillations of the temperature 

 of the air are slighter in Ibrests than upon uuwooded ground. In the 

 hours and years, particularly when the maximum of heat was attained, 

 the sum total of the latter in the woods was much less than in the open 

 fields. 



In accordance with this the temperature of wooded surfaces in the 

 warm years is considerably lower than that of uuwooded surfaces.t 



*The factof the influenco of height upon tbe results of the iain-iuea«nies has frequent 

 coutiimation ; for instance, in Mollendorf's work, page 102. it appears that of several 

 stations the lower recorded from 13 to (50 per cent, more rain than the higher. 



t According to Ebermayer, the .yearly oscillations of temperature in the woods (SO'-'.O 

 C.) are 7° C. less than in the open fields. The yearly maximum of temperature is found 

 to 1)0 5'-'.2 lower. Likewise the daily oscillations of temperature in summer amount to 

 50.9 C. less than that of the open fields. The temperature of the soil of forest-laud 

 was, in summer, 40.O C. lees than that of the uuwooded soil. (Ebermayer's Physical 

 Influence of the Woods, Journal of Meteorology, vol. 8, pp. 209 and 232.) 



