WtlPW^G OF TREES. 215 



LETTEE LXXI. 



TO THE SAME. 



Selborne, Feb. 7, 1776. 

 Dear Sir, — In heavy fogs, on elevated situations especially, 

 trees are perfect alembics ; and no one that has not attended 

 to such matters can imagine how much water one tree will 

 distil in a night's time, by condensing the vapour, which 

 trickles down the twigs and boughs, so as to make the 

 ground below quite in a float. In Newton-lane, in October, 

 1775, On a misty day, a particular oak in leaf dropped so fast 

 that the cart-way stood in puddles, and the ruts ran with 

 water, though the ground in general was dusty. 



In some of our smaller islands in the "West Indies, if I 

 mistake not, there are no springs or rivers ; but the people 

 are supplied with that necessary element, water, merely by 

 the dripping of some large tall trees, which, standing in the 

 bosom of a mountain, keep their heads constantly enveloped 

 with fogs and clouds, from which they dispense their kindly, 

 never-ceasing moisture ; and so render those districts 

 habitable by condensation alone. 



Trees in leaf have such a vast proportion more of surface 

 than those that are naked, that, in theory, their condensa- 

 tions should greatly exceed those that are stripped of their 

 leaves ; but, as the former imbibe also a great quantity of 

 moisture, it is difficult to say which dr'p most : but this I 

 know, that deciduous trees, that are entwined with much 

 ivy, seem to distil the greatest quantity, Ivy leaves are 

 smooth, and thick, and cold, and therefore condense very 

 fast ; and besides, evergreens imbibe very little.* These 



• It has beeu supposed that trees, by condensinj^ the moisture of the aii 

 IQ foggy weather, materially affect the climate, and that thickly wooded 

 eouiitiies must necessarily be colder and more humid than naked savannahs. 

 There can be little doubt that such is the case. When some North American 

 Indians made the discovery that the wild cattle of the prairies got amidst the 

 %mcke of a burning forest to drive away the flies, thej set fire to large tractg 



