176 THE NATURAL HISTORY 



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 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 ever-greens 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 others. 



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 forests have been grubbed and cleared, 

 all bodies of water are much diminished ; so that some 

 streams, that were very considerable a century ago, will 

 not now drive a common mill. 1 Besides, most woodlands, 

 forests, and chases, with us abound with pools and mor- 

 asses ; no doubt for the reason given above. 



To a thinking mind few phenomena are more strange 



1 Vide Kalm's Travels to North-America. 



