TREES ATTRACTORS OF HUMIDITY. 59 



a hill in the month of March. The weather 

 had previously been very fine and dry, and the 

 road in a dusty state ; but a fog coming on, an 

 ash tree hanging over the road was dripping with 

 water so copiously, that the road beneath was in 

 a puddle, when the other parts continued dry, and 

 manifested no appearance of humidity. That 

 leaves imbibe moisture by one set of vessels, and 

 discharge them by another, is well known; but 

 these imbibings are never discharged in falling 

 drops : the real mystery was, the fog in its pro- 

 gress was impeded by the boughs of the tree, and 

 gradually collected on the exposed side of them, 

 until it became drops of water, whereas the sur- 

 rounding counUy had only a mist flying over it. 

 Thus, in fact, the tree was no attractor, but a con- 

 denser ; the gate of a field will in the same manner 

 run down with water on the one side, and be dry 

 on the other ; as will a stick, or a post, from the 

 same cause. It is upon this principle that currents 

 of air will be found under trees in summer, when 

 little is perceived in open places; and the under 

 leaves and sprays will be curled and scorched at- 

 times, when the parts above are uninjured. The 

 air in its passage being stopped and condensed 

 against the foliage of the tree, it accordingly de- 

 scends along its surface or front, and escapes at the 

 bottom, where there are no branches or leaves to 

 interrupt its progress. In winter there is little to 

 impede the breeze in its course, and it passes 

 through ; consequently, at this season the air under 



