176 The Natural History 



the ruls ran ^YiLh water, though the ground in general was 

 dusty. 



In some of our smaller islands in the AVest- Indies, if I 

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

 are supplied with that necessary element, water, merely 

 by the dripj)ing 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 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 others. 



Trees perspire profusely, condense largely, and check 

 evaporation so much, that woods are always mcjist : 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.^ Besides, most 

 woodlands, forests, and chases with us abound with pools 

 and morasses ; no doubt for the reason given above. 



To a thinkmg mind few phenomena are more strange 

 than the state of little ponds on the summits of chalk- 

 hills, many of which are never dry in the most trying 



^ Vide Kalm's Travels (0 Norih America. 



