242 RESULTS OF COMPARATIVE OBSERVATIONS: BAVARIA. 



The evaporation at night is from a third to a half less than in the 

 clay time, and by day it is greater in the sun than in the shade. Under 

 a clear sky, with a north and northeast wind,i even the soil will dry 

 quickly. The favorable effects from loosening a wet soil, and the ne- 

 cessity of rolling a light one, in dry weather, explain themselves from 

 the above. The moisture evaporated trom a water-surface is carried to 

 other places by currents of wind ; and a large part of the moisture in 

 the air is brought from the sea. It is, under favorable conditions, 

 returned to the earth as snow or rain. 



Having shown that the forest-air, in the yearly mean, is colder, and rel- 

 atively moister in the woods than in the fields, and the force of the winds 

 being much less in the former, it follows that in the forest less water 

 evaporates from the ground than in the fields. According to observa- 

 tions in the year 1858-59, the evaporation from a free water surface, in 

 Paris square feet, at the several stations, amounted to the following, in 

 Paris cubic inches : 



As a mean general average for all observations, the evaporation was : 



In the forests, the evaporation from a free water surface was, in the 

 yearly average, C4 per cent, less than in the open fields ; or in other 

 words, where 100 cuibic inches would be evaporated from a square foot 

 in an open exposure, but 36 inches would be changed to vapor in the 

 woods. This reduced evaporation in the latter is, of course, the prin- 

 cipal cause of the greater moisture of the soil in wood-lands. 



Amount of ex^aporation from a free icater surface at different seasons. 



Evaporation, like the temperature and moisture of the air, reached its 

 maximum in summer, followed in descending order by spring, autumn, 

 and winter. The evaporation was most at the most elevated station. 



' This is said of Germany ; but with us, the drjiug winds are north, northwest, west, 

 and especially in the Western States, in summer, the southwest. In all cases, it may 

 b-i stated as the general rule, that winds coming from the interior of continents are 

 dry, and that ocean winds are moist. 



