470 



Notes on the Influence 



[No. 36, 



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 Octo- 

 ber, 1675, 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, it" I mistake not, there are no springs or 

 rivers, but the people are supplied with that necessary element, 

 water, merelj' by the dripping of some large tall trees, which stand- 

 ing in the bosom of a mountain, keep their heads constantly enve- 

 loped 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 con- 

 densation should greatly exceed those that are stripped of their leaves, 

 but as the former imbibe also a great quantity of moisture, it is diffi- 

 cult 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 pe- 

 rennial, and show them how advantageous some trees are in preference 

 toothers. Trees perspire profusely, condense largely,' and check eva- 

 poration so much, that woods are alwaj^s 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. Besides most wood-lands, forests, and chases, 

 with us, abound with pools and morasses, no doubt for the reason 

 given above. Again, Dr. Hales in his vegetable statics, advances 

 from experience, that the moister the earth is, the more dew falls on 

 it in a night; and more than a double quantity of dew falls on 

 a surface of water, than there does on an equal surface of moist 

 earth. Hence we see that water, by its coolness, is enabled to assi- 

 milate to itself a larger quantity of moisture nightly by condensation. 



