NATURAL HISTORY OF SELBORNE. 199 



LETTER XXIX, 



TO THE SAME. 



SELBORNE, Feb. jtk, 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 condensations 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 drip most ; but this I know, that deciduous trees that are en- 

 twined 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 facts may 

 furnish the intelligent with hints concerning what sorts of trees they 

 should plant round small ponds that they would wish to be perennial ; 

 and show them how advantageous some trees are in preference to 

 Bothers. 



Trees perspire profusely, condense largely, and check evaporation 

 so much, that woods are always moist ; no wonder, therefore, that 

 they contribute much to pools and streams. 



That trees are great promoters of lakes and rivers appears from 

 a well-known fact in North America : for, since the woods and 



